Merge bk-internal.mysql.com:/home/bk/mysql-4.1-engines

into  chilla.local:/home/mydev/mysql-4.1-bug8283-one


include/my_sys.h:
  Auto merged

10 files changed, 1132 insertions, 234 deletions

diff --git a/include/my_sys.h b/include/my_sys.h
index 46e09e8ddf4..4c9a7a7964c 100644
--- a/include/my_sys.h
+++ b/include/my_sys.h
@@ -325,12 +325,18 @@ typedef int (*IO_CACHE_CALLBACK)(struct st_io_cache*);
 #ifdef THREAD
 typedef struct st_io_cache_share
 {
-  /* to sync on reads into buffer */
-  pthread_mutex_t mutex;
-  pthread_cond_t  cond;
-  int             count, total;
-  /* actual IO_CACHE that filled the buffer */
-  struct st_io_cache *active;
+  pthread_mutex_t       mutex;           /* To sync on reads into buffer. */
+  pthread_cond_t        cond;            /* To wait for signals. */
+  pthread_cond_t        cond_writer;     /* For a synchronized writer. */
+  /* Offset in file corresponding to the first byte of buffer. */
+  my_off_t              pos_in_file;
+  /* If a synchronized write cache is the source of the data. */
+  struct st_io_cache    *source_cache;
+  byte                  *buffer;         /* The read buffer. */
+  byte                  *read_end;       /* Behind last valid byte of buffer. */
+  int                   running_threads; /* threads not in lock. */
+  int                   total_threads;   /* threads sharing the cache. */
+  int                   error;           /* Last error. */
 #ifdef NOT_YET_IMPLEMENTED
   /* whether the structure should be free'd */
   my_bool alloced;
@@ -672,8 +678,8 @@ extern void setup_io_cache(IO_CACHE* info);
 extern int _my_b_read(IO_CACHE *info,byte *Buffer,uint Count);
 #ifdef THREAD
 extern int _my_b_read_r(IO_CACHE *info,byte *Buffer,uint Count);
-extern void init_io_cache_share(IO_CACHE *info,
-				IO_CACHE_SHARE *s, uint num_threads);
+extern void init_io_cache_share(IO_CACHE *read_cache, IO_CACHE_SHARE *cshare,
+                                IO_CACHE *write_cache, uint num_threads);
 extern void remove_io_thread(IO_CACHE *info);
 #endif
 extern int _my_b_seq_read(IO_CACHE *info,byte *Buffer,uint Count);
diff --git a/include/myisam.h b/include/myisam.h
index c2d3d99a414..0a808070748 100644
--- a/include/myisam.h
+++ b/include/myisam.h
@@ -345,7 +345,7 @@ typedef struct st_mi_check_param
   uint testflag, key_cache_block_size;
   uint8 language;
   my_bool using_global_keycache, opt_lock_memory, opt_follow_links;
-  my_bool retry_repair, force_sort, calc_checksum;
+  my_bool retry_repair, force_sort;
   char temp_filename[FN_REFLEN],*isam_file_name;
   MY_TMPDIR *tmpdir;
   int tmpfile_createflag;
diff --git a/myisam/mi_check.c b/myisam/mi_check.c
index 301becf9c62..b07c9904247 100644
--- a/myisam/mi_check.c
+++ b/myisam/mi_check.c
@@ -16,6 +16,31 @@
 
 /* Describe, check and repair of MyISAM tables */
 
+/*
+  About checksum calculation.
+
+  There are two types of checksums. Table checksum and row checksum.
+
+  Row checksum is an additional byte at the end of dynamic length
+  records. It must be calculated if the table is configured for them.
+  Otherwise they must not be used. The variable
+  MYISAM_SHARE::calc_checksum determines if row checksums are used.
+  MI_INFO::checksum is used as temporary storage during row handling.
+  For parallel repair we must assure that only one thread can use this
+  variable. There is no problem on the write side as this is done by one
+  thread only. But when checking a record after read this could go
+  wrong. But since all threads read through a common read buffer, it is
+  sufficient if only one thread checks it.
+
+  Table checksum is an eight byte value in the header of the index file.
+  It can be calculated even if row checksums are not used. The variable
+  MI_CHECK::glob_crc is calculated over all records.
+  MI_SORT_PARAM::calc_checksum determines if this should be done. This
+  variable is not part of MI_CHECK because it must be set per thread for
+  parallel repair. The global glob_crc must be changed by one thread
+  only. And it is sufficient to calculate the checksum once only.
+*/
+
 #include "ftdefs.h"
 #include <m_ctype.h>
 #include <stdarg.h>
@@ -41,8 +66,7 @@ static int chk_index(MI_CHECK *param, MI_INFO *info,MI_KEYDEF *keyinfo,
 		     ha_checksum *key_checksum, uint level);
 static uint isam_key_length(MI_INFO *info,MI_KEYDEF *keyinfo);
 static ha_checksum calc_checksum(ha_rows count);
-static int writekeys(MI_CHECK *param, MI_INFO *info,byte *buff,
-		     my_off_t filepos);
+static int writekeys(MI_SORT_PARAM *sort_param);
 static int sort_one_index(MI_CHECK *param, MI_INFO *info,MI_KEYDEF *keyinfo,
 			  my_off_t pagepos, File new_file);
 static int sort_key_read(MI_SORT_PARAM *sort_param,void *key);
@@ -1101,7 +1125,8 @@ int chk_data_link(MI_CHECK *param, MI_INFO *info,int extend)
 	goto err;
       start_recpos=pos;
       splits++;
-      VOID(_mi_pack_get_block_info(info,&block_info, -1, start_recpos));
+      VOID(_mi_pack_get_block_info(info, &info->bit_buff, &block_info,
+                                   &info->rec_buff, -1, start_recpos));
       pos=block_info.filepos+block_info.rec_len;
       if (block_info.rec_len < (uint) info->s->min_pack_length ||
 	  block_info.rec_len > (uint) info->s->max_pack_length)
@@ -1115,7 +1140,8 @@ int chk_data_link(MI_CHECK *param, MI_INFO *info,int extend)
       if (_mi_read_cache(&param->read_cache,(byte*) info->rec_buff,
 			block_info.filepos, block_info.rec_len, READING_NEXT))
 	goto err;
-      if (_mi_pack_rec_unpack(info,record,info->rec_buff,block_info.rec_len))
+      if (_mi_pack_rec_unpack(info, &info->bit_buff, record,
+                              info->rec_buff, block_info.rec_len))
       {
 	mi_check_print_error(param,"Found wrong record at %s",
 			     llstr(start_recpos,llbuff));
@@ -1399,7 +1425,7 @@ int mi_repair(MI_CHECK *param, register MI_INFO *info,
   info->state->empty=0;
   param->glob_crc=0;
   if (param->testflag & T_CALC_CHECKSUM)
-    param->calc_checksum=1;
+    sort_param.calc_checksum= 1;
 
   info->update= (short) (HA_STATE_CHANGED | HA_STATE_ROW_CHANGED);
   for (i=0 ; i < info->s->base.keys ; i++)
@@ -1423,7 +1449,7 @@ int mi_repair(MI_CHECK *param, register MI_INFO *info,
   lock_memory(param);			/* Everything is alloced */
   while (!(error=sort_get_next_record(&sort_param)))
   {
-    if (writekeys(param,info,(byte*)sort_param.record,sort_param.filepos))
+    if (writekeys(&sort_param))
     {
       if (my_errno != HA_ERR_FOUND_DUPP_KEY)
 	goto err;
@@ -1568,11 +1594,13 @@ err:
 
 /* Uppate keyfile when doing repair */
 
-static int writekeys(MI_CHECK *param, register MI_INFO *info, byte *buff,
-		     my_off_t filepos)
+static int writekeys(MI_SORT_PARAM *sort_param)
 {
   register uint i;
-  uchar *key;
+  uchar    *key;
+  MI_INFO  *info=   sort_param->sort_info->info;
+  byte     *buff=   sort_param->record;
+  my_off_t filepos= sort_param->filepos;
   DBUG_ENTER("writekeys");
 
   key=info->lastkey+info->s->base.max_key_length;
@@ -1626,8 +1654,8 @@ static int writekeys(MI_CHECK *param, register MI_INFO *info, byte *buff,
     }
   }
   /* Remove checksum that was added to glob_crc in sort_get_next_record */
-  if (param->calc_checksum)
-    param->glob_crc-= info->checksum;
+  if (sort_param->calc_checksum)
+    sort_param->sort_info->param->glob_crc-= info->checksum;
   DBUG_PRINT("error",("errno: %d",my_errno));
   DBUG_RETURN(-1);
 } /* writekeys */
@@ -2133,7 +2161,7 @@ int mi_repair_by_sort(MI_CHECK *param, register MI_INFO *info,
   del=info->state->del;
   param->glob_crc=0;
   if (param->testflag & T_CALC_CHECKSUM)
-    param->calc_checksum=1;
+    sort_param.calc_checksum= 1;
 
   rec_per_key_part= param->rec_per_key_part;
   for (sort_param.key=0 ; sort_param.key < share->base.keys ;
@@ -2195,7 +2223,8 @@ int mi_repair_by_sort(MI_CHECK *param, register MI_INFO *info,
       param->retry_repair=1;
       goto err;
     }
-    param->calc_checksum=0;			/* No need to calc glob_crc */
+    /* No need to calculate checksum again. */
+    sort_param.calc_checksum= 0;
 
     /* Set for next loop */
     sort_info.max_records= (ha_rows) info->state->records;
@@ -2358,6 +2387,28 @@ err:
     Each key is handled by a separate thread.
     TODO: make a number of threads a parameter
 
+    In parallel repair we use one thread per index. There are two modes:
+
+    Quick
+
+      Only the indexes are rebuilt. All threads share a read buffer.
+      Every thread that needs fresh data in the buffer enters the shared
+      cache lock. The last thread joining the lock reads the buffer from
+      the data file and wakes all other threads.
+
+    Non-quick
+
+      The data file is rebuilt and all indexes are rebuilt to point to
+      the new record positions. One thread is the master thread. It
+      reads from the old data file and writes to the new data file. It
+      also creates one of the indexes. The other threads read from a
+      buffer which is filled by the master. If they need fresh data,
+      they enter the shared cache lock. If the masters write buffer is
+      full, it flushes it to the new data file and enters the shared
+      cache lock too. When all threads joined in the lock, the master
+      copies its write buffer to the read buffer for the other threads
+      and wakes them.
+
   RESULT
     0	ok
     <>0	Error
@@ -2380,6 +2431,7 @@ int mi_repair_parallel(MI_CHECK *param, register MI_INFO *info,
   ulong   *rec_per_key_part;
   HA_KEYSEG *keyseg;
   char llbuff[22];
+  IO_CACHE new_data_cache; /* For non-quick repair. */
   IO_CACHE_SHARE io_share;
   SORT_INFO sort_info;
   ulonglong key_map=share->state.key_map;
@@ -2401,19 +2453,55 @@ int mi_repair_parallel(MI_CHECK *param, register MI_INFO *info,
   if (info->s->options & (HA_OPTION_CHECKSUM | HA_OPTION_COMPRESS_RECORD))
     param->testflag|=T_CALC_CHECKSUM;
 
+  /*
+    Quick repair (not touching data file, rebuilding indexes):
+    {
+      Read  cache is (MI_CHECK *param)->read_cache using info->dfile.
+    }
+
+    Non-quick repair (rebuilding data file and indexes):
+    {
+      Master thread:
+
+        Read  cache is (MI_CHECK *param)->read_cache using info->dfile.
+        Write cache is (MI_INFO   *info)->rec_cache  using new_file.
+
+      Slave threads:
+
+        Read  cache is new_data_cache synced to master rec_cache.
+
+      The final assignment of the filedescriptor for rec_cache is done
+      after the cache creation.
+
+      Don't check file size on new_data_cache, as the resulting file size
+      is not known yet.
+
+      As rec_cache and new_data_cache are synced, write_buffer_length is
+      used for the read cache 'new_data_cache'. Both start at the same
+      position 'new_header_length'.
+    }
+  */
+  DBUG_PRINT("info", ("is quick repair: %d", rep_quick));
   bzero((char*)&sort_info,sizeof(sort_info));
+  /* Initialize pthread structures before goto err. */
+  pthread_mutex_init(&sort_info.mutex, MY_MUTEX_INIT_FAST);
+  pthread_cond_init(&sort_info.cond, 0);
+
   if (!(sort_info.key_block=
-	alloc_key_blocks(param,
-			 (uint) param->sort_key_blocks,
-			 share->base.max_key_block_length))
-      || init_io_cache(&param->read_cache,info->dfile,
-		       (uint) param->read_buffer_length,
-		       READ_CACHE,share->pack.header_length,1,MYF(MY_WME)) ||
-      (! rep_quick &&
-       init_io_cache(&info->rec_cache,info->dfile,
-		     (uint) param->write_buffer_length,
-		     WRITE_CACHE,new_header_length,1,
-		     MYF(MY_WME | MY_WAIT_IF_FULL) & param->myf_rw)))
+	alloc_key_blocks(param, (uint) param->sort_key_blocks,
+			 share->base.max_key_block_length)) ||
+      init_io_cache(&param->read_cache, info->dfile,
+                    (uint) param->read_buffer_length,
+                    READ_CACHE, share->pack.header_length, 1, MYF(MY_WME)) ||
+      (!rep_quick &&
+       (init_io_cache(&info->rec_cache, info->dfile,
+                      (uint) param->write_buffer_length,
+                      WRITE_CACHE, new_header_length, 1,
+                      MYF(MY_WME | MY_WAIT_IF_FULL) & param->myf_rw) ||
+        init_io_cache(&new_data_cache, -1,
+                      (uint) param->write_buffer_length,
+                      READ_CACHE, new_header_length, 1,
+                      MYF(MY_WME | MY_DONT_CHECK_FILESIZE)))))
     goto err;
   sort_info.key_block_end=sort_info.key_block+param->sort_key_blocks;
   info->opt_flag|=WRITE_CACHE_USED;
@@ -2504,8 +2592,6 @@ int mi_repair_parallel(MI_CHECK *param, register MI_INFO *info,
 
   del=info->state->del;
   param->glob_crc=0;
-  if (param->testflag & T_CALC_CHECKSUM)
-    param->calc_checksum=1;
 
   if (!(sort_param=(MI_SORT_PARAM *)
         my_malloc((uint) share->base.keys *
@@ -2555,6 +2641,7 @@ int mi_repair_parallel(MI_CHECK *param, register MI_INFO *info,
     sort_param[i].sort_info=&sort_info;
     sort_param[i].master=0;
     sort_param[i].fix_datafile=0;
+    sort_param[i].calc_checksum= 0;
 
     sort_param[i].filepos=new_header_length;
     sort_param[i].max_pos=sort_param[i].pos=share->pack.header_length;
@@ -2591,19 +2678,45 @@ int mi_repair_parallel(MI_CHECK *param, register MI_INFO *info,
   sort_info.total_keys=i;
   sort_param[0].master= 1;
   sort_param[0].fix_datafile= (my_bool)(! rep_quick);
+  sort_param[0].calc_checksum= test(param->testflag & T_CALC_CHECKSUM);
 
   sort_info.got_error=0;
-  pthread_mutex_init(&sort_info.mutex, MY_MUTEX_INIT_FAST);
-  pthread_cond_init(&sort_info.cond, 0);
   pthread_mutex_lock(&sort_info.mutex);
 
-  init_io_cache_share(&param->read_cache, &io_share, i);
+  /*
+    Initialize the I/O cache share for use with the read caches and, in
+    case of non-quick repair, the write cache. When all threads join on
+    the cache lock, the writer copies the write cache contents to the
+    read caches.
+  */
+  if (i > 1)
+  {
+    if (rep_quick)
+      init_io_cache_share(&param->read_cache, &io_share, NULL, i);
+    else
+      init_io_cache_share(&new_data_cache, &io_share, &info->rec_cache, i);
+  }
+  else
+    io_share.total_threads= 0; /* share not used */
+
   (void) pthread_attr_init(&thr_attr);
   (void) pthread_attr_setdetachstate(&thr_attr,PTHREAD_CREATE_DETACHED);
 
   for (i=0 ; i < sort_info.total_keys ; i++)
   {
-    sort_param[i].read_cache=param->read_cache;
+    /*
+      Copy the properly initialized IO_CACHE structure so that every
+      thread has its own copy. In quick mode param->read_cache is shared
+      for use by all threads. In non-quick mode all threads but the
+      first copy the shared new_data_cache, which is synchronized to the
+      write cache of the first thread. The first thread copies
+      param->read_cache, which is not shared.
+    */
+    sort_param[i].read_cache= ((rep_quick || !i) ? param->read_cache :
+                               new_data_cache);
+    DBUG_PRINT("io_cache_share", ("thread: %u  read_cache: 0x%lx",
+                                  i, (long) &sort_param[i].read_cache));
+
     /*
       two approaches: the same amount of memory for each thread
       or the memory for the same number of keys for each thread...
@@ -2621,7 +2734,10 @@ int mi_repair_parallel(MI_CHECK *param, register MI_INFO *info,
 		       (void *) (sort_param+i)))
     {
       mi_check_print_error(param,"Cannot start a repair thread");
-      remove_io_thread(&param->read_cache);
+      /* Cleanup: Detach from the share. Avoid others to be blocked. */
+      if (io_share.total_threads)
+        remove_io_thread(&sort_param[i].read_cache);
+      DBUG_PRINT("error", ("Cannot start a repair thread"));
       sort_info.got_error=1;
     }
     else
@@ -2643,6 +2759,11 @@ int mi_repair_parallel(MI_CHECK *param, register MI_INFO *info,
 
   if (sort_param[0].fix_datafile)
   {
+    /*
+      Append some nuls to the end of a memory mapped file. Destroy the
+      write cache. The master thread did already detach from the share
+      by remove_io_thread() in sort.c:thr_find_all_keys().
+    */
     if (write_data_suffix(&sort_info,1) || end_io_cache(&info->rec_cache))
       goto err;
     if (param->testflag & T_SAFE_REPAIR)
@@ -2658,8 +2779,14 @@ int mi_repair_parallel(MI_CHECK *param, register MI_INFO *info,
       sort_param->filepos;
     /* Only whole records */
     share->state.version=(ulong) time((time_t*) 0);
+
+    /*
+      Exchange the data file descriptor of the table, so that we use the
+      new file from now on.
+     */
     my_close(info->dfile,MYF(0));
     info->dfile=new_file;
+
     share->data_file_type=sort_info.new_data_file_type;
     share->pack.header_length=(ulong) new_header_length;
   }
@@ -2714,7 +2841,20 @@ int mi_repair_parallel(MI_CHECK *param, register MI_INFO *info,
 
 err:
   got_error|= flush_blocks(param, share->key_cache, share->kfile);
+  /*
+    Destroy the write cache. The master thread did already detach from
+    the share by remove_io_thread() or it was not yet started (if the
+    error happend before creating the thread).
+  */
   VOID(end_io_cache(&info->rec_cache));
+  /*
+    Destroy the new data cache in case of non-quick repair. All slave
+    threads did either detach from the share by remove_io_thread()
+    already or they were not yet started (if the error happend before
+    creating the threads).
+  */
+  if (!rep_quick)
+    VOID(end_io_cache(&new_data_cache));
   if (!got_error)
   {
     /* Replace the actual file with the temporary file */
@@ -2845,12 +2985,41 @@ static int sort_ft_key_read(MI_SORT_PARAM *sort_param, void *key)
 } /* sort_ft_key_read */
 
 
-	/* Read next record from file using parameters in sort_info */
-	/* Return -1 if end of file, 0 if ok and > 0 if error */
+/*
+  Read next record from file using parameters in sort_info.
+
+  SYNOPSIS
+    sort_get_next_record()
+      sort_param                Information about and for the sort process
+
+  NOTE
+
+    Dynamic Records With Non-Quick Parallel Repair
+
+      For non-quick parallel repair we use a synchronized read/write
+      cache. This means that one thread is the master who fixes the data
+      file by reading each record from the old data file and writing it
+      to the new data file. By doing this the records in the new data
+      file are written contiguously. Whenever the write buffer is full,
+      it is copied to the read buffer. The slaves read from the read
+      buffer, which is not associated with a file. Thus read_cache.file
+      is -1. When using _mi_read_cache(), the slaves must always set
+      flag to READING_NEXT so that the function never tries to read from
+      file. This is safe because the records are contiguous. There is no
+      need to read outside the cache. This condition is evaluated in the
+      variable 'parallel_flag' for quick reference. read_cache.file must
+      be >= 0 in every other case.
+
+  RETURN
+    -1          end of file
+    0           ok
+    > 0         error
+*/
 
 static int sort_get_next_record(MI_SORT_PARAM *sort_param)
 {
   int searching;
+  int parallel_flag;
   uint found_record,b_type,left_length;
   my_off_t pos;
   byte *to;
@@ -2888,7 +3057,7 @@ static int sort_get_next_record(MI_SORT_PARAM *sort_param)
       sort_param->max_pos=(sort_param->pos+=share->base.pack_reclength);
       if (*sort_param->record)
       {
-	if (param->calc_checksum)
+	if (sort_param->calc_checksum)
 	  param->glob_crc+= (info->checksum=
 			     mi_static_checksum(info,sort_param->record));
 	DBUG_RETURN(0);
@@ -2903,6 +3072,7 @@ static int sort_get_next_record(MI_SORT_PARAM *sort_param)
     LINT_INIT(to);
     pos=sort_param->pos;
     searching=(sort_param->fix_datafile && (param->testflag & T_EXTEND));
+    parallel_flag= (sort_param->read_cache.file < 0) ? READING_NEXT : 0;
     for (;;)
     {
       found_record=block_info.second_read= 0;
@@ -2933,7 +3103,7 @@ static int sort_get_next_record(MI_SORT_PARAM *sort_param)
                            (byte*) block_info.header,pos,
 			   MI_BLOCK_INFO_HEADER_LENGTH,
 			   (! found_record ? READING_NEXT : 0) |
-			   READING_HEADER))
+                           parallel_flag | READING_HEADER))
 	{
 	  if (found_record)
 	  {
@@ -3110,9 +3280,31 @@ static int sort_get_next_record(MI_SORT_PARAM *sort_param)
 			      llstr(sort_param->start_recpos,llbuff));
 	  goto try_next;
 	}
-	if (_mi_read_cache(&sort_param->read_cache,to,block_info.filepos,
-			   block_info.data_len,
-			   (found_record == 1 ? READING_NEXT : 0)))
+        /*
+          Copy information that is already read. Avoid accessing data
+          below the cache start. This could happen if the header
+          streched over the end of the previous buffer contents.
+        */
+        {
+          uint header_len= (uint) (block_info.filepos - pos);
+          uint prefetch_len= (MI_BLOCK_INFO_HEADER_LENGTH - header_len);
+
+          if (prefetch_len > block_info.data_len)
+            prefetch_len= block_info.data_len;
+          if (prefetch_len)
+          {
+            memcpy(to, block_info.header + header_len, prefetch_len);
+            block_info.filepos+= prefetch_len;
+            block_info.data_len-= prefetch_len;
+            left_length-= prefetch_len;
+            to+= prefetch_len;
+          }
+        }
+        if (block_info.data_len &&
+            _mi_read_cache(&sort_param->read_cache,to,block_info.filepos,
+                           block_info.data_len,
+                           (found_record == 1 ? READING_NEXT : 0) |
+                           parallel_flag))
 	{
 	  mi_check_print_info(param,
 			      "Read error for block at: %s (error: %d); Skipped",
@@ -3142,13 +3334,14 @@ static int sort_get_next_record(MI_SORT_PARAM *sort_param)
       {
 	if (sort_param->read_cache.error < 0)
 	  DBUG_RETURN(1);
-	if (info->s->calc_checksum)
-	  info->checksum=mi_checksum(info,sort_param->record);
+	if (sort_param->calc_checksum)
+	  info->checksum= mi_checksum(info, sort_param->record);
 	if ((param->testflag & (T_EXTEND | T_REP)) || searching)
 	{
 	  if (_mi_rec_check(info, sort_param->record, sort_param->rec_buff,
                             sort_param->find_length,
                             (param->testflag & T_QUICK) &&
+                            sort_param->calc_checksum &&
                             test(info->s->calc_checksum)))
 	  {
 	    mi_check_print_info(param,"Found wrong packed record at %s",
@@ -3156,7 +3349,7 @@ static int sort_get_next_record(MI_SORT_PARAM *sort_param)
 	    goto try_next;
 	  }
 	}
-	if (param->calc_checksum)
+	if (sort_param->calc_checksum)
 	  param->glob_crc+= info->checksum;
 	DBUG_RETURN(0);
       }
@@ -3183,7 +3376,8 @@ static int sort_get_next_record(MI_SORT_PARAM *sort_param)
 	DBUG_RETURN(1);		/* Something wrong with data */
       }
       sort_param->start_recpos=sort_param->pos;
-      if (_mi_pack_get_block_info(info,&block_info,-1,sort_param->pos))
+      if (_mi_pack_get_block_info(info, &sort_param->bit_buff, &block_info,
+                                  &sort_param->rec_buff, -1, sort_param->pos))
 	DBUG_RETURN(-1);
       if (!block_info.rec_len &&
 	  sort_param->pos + MEMMAP_EXTRA_MARGIN ==
@@ -3207,15 +3401,14 @@ static int sort_get_next_record(MI_SORT_PARAM *sort_param)
 			      llstr(sort_param->pos,llbuff));
 	continue;
       }
-      if (_mi_pack_rec_unpack(info,sort_param->record,sort_param->rec_buff,
-			      block_info.rec_len))
+      if (_mi_pack_rec_unpack(info, &sort_param->bit_buff, sort_param->record,
+                              sort_param->rec_buff, block_info.rec_len))
       {
 	if (! searching)
 	  mi_check_print_info(param,"Found wrong record at %s",
 			      llstr(sort_param->pos,llbuff));
 	continue;
       }
-      info->checksum=mi_checksum(info,sort_param->record);
       if (!sort_param->fix_datafile)
       {
 	sort_param->filepos=sort_param->pos;
@@ -3225,8 +3418,9 @@ static int sort_get_next_record(MI_SORT_PARAM *sort_param)
       sort_param->max_pos=(sort_param->pos=block_info.filepos+
 			 block_info.rec_len);
       info->packed_length=block_info.rec_len;
-      if (param->calc_checksum)
-	param->glob_crc+= info->checksum;
+      if (sort_param->calc_checksum)
+	param->glob_crc+= (info->checksum=
+                           mi_checksum(info, sort_param->record));
       DBUG_RETURN(0);
     }
   }
@@ -3234,7 +3428,20 @@ static int sort_get_next_record(MI_SORT_PARAM *sort_param)
 }
 
 
-	/* Write record to new file */
+/*
+  Write record to new file.
+
+  SYNOPSIS
+    sort_write_record()
+      sort_param                Sort parameters.
+
+  NOTE
+    This is only called by a master thread if parallel repair is used.
+
+  RETURN
+    0           OK
+    1           Error
+*/
 
 int sort_write_record(MI_SORT_PARAM *sort_param)
 {
@@ -3283,6 +3490,7 @@ int sort_write_record(MI_SORT_PARAM *sort_param)
 	}
 	from=sort_info->buff+ALIGN_SIZE(MI_MAX_DYN_BLOCK_HEADER);
       }
+      /* We can use info->checksum here as only one thread calls this. */
       info->checksum=mi_checksum(info,sort_param->record);
       reclength=_mi_rec_pack(info,from,sort_param->record);
       flag=0;
@@ -3692,7 +3900,7 @@ static int sort_delete_record(MI_SORT_PARAM *sort_param)
 	DBUG_RETURN(1);
       }
     }
-    if (param->calc_checksum)
+    if (sort_param->calc_checksum)
       param->glob_crc-=(*info->s->calc_checksum)(info, sort_param->record);
   }
   error=flush_io_cache(&info->rec_cache) || (*info->s->delete_record)(info);
diff --git a/myisam/mi_open.c b/myisam/mi_open.c
index a5b303f86d4..4f298397615 100644
--- a/myisam/mi_open.c
+++ b/myisam/mi_open.c
@@ -201,7 +201,10 @@ MI_INFO *mi_open(const char *name, int mode, uint open_flags)
 	 ((open_flags & HA_OPEN_ABORT_IF_CRASHED) &&
 	  (my_disable_locking && share->state.open_count))))
     {
-      DBUG_PRINT("error",("Table is marked as crashed"));
+      DBUG_PRINT("error",("Table is marked as crashed. open_flags: %u  "
+                          "changed: %u  open_count: %u  !locking: %d",
+                          open_flags, share->state.changed,
+                          share->state.open_count, my_disable_locking));
       my_errno=((share->state.changed & STATE_CRASHED_ON_REPAIR) ?
 		HA_ERR_CRASHED_ON_REPAIR : HA_ERR_CRASHED_ON_USAGE);
       goto err;
diff --git a/myisam/mi_packrec.c b/myisam/mi_packrec.c
index 0edb3ac1d5d..feb8d33b015 100644
--- a/myisam/mi_packrec.c
+++ b/myisam/mi_packrec.c
@@ -101,7 +101,8 @@ static uint fill_and_get_bits(MI_BIT_BUFF *bit_buff,uint count);
 static void fill_buffer(MI_BIT_BUFF *bit_buff);
 static uint max_bit(uint value);
 #ifdef HAVE_MMAP
-static uchar *_mi_mempack_get_block_info(MI_INFO *myisam,MI_BLOCK_INFO *info,
+static uchar *_mi_mempack_get_block_info(MI_INFO *myisam, MI_BIT_BUFF *bit_buff,
+                                         MI_BLOCK_INFO *info, byte **rec_buff_p,
 					 uchar *header);
 #endif
 
@@ -436,13 +437,15 @@ int _mi_read_pack_record(MI_INFO *info, my_off_t filepos, byte *buf)
     DBUG_RETURN(-1);			/* _search() didn't find record */
 
   file=info->dfile;
-  if (_mi_pack_get_block_info(info, &block_info, file, filepos))
+  if (_mi_pack_get_block_info(info, &info->bit_buff, &block_info,
+                              &info->rec_buff, file, filepos))
     goto err;
   if (my_read(file,(byte*) info->rec_buff + block_info.offset ,
 	      block_info.rec_len - block_info.offset, MYF(MY_NABP)))
     goto panic;
   info->update|= HA_STATE_AKTIV;
-  DBUG_RETURN(_mi_pack_rec_unpack(info,buf,info->rec_buff,block_info.rec_len));
+  DBUG_RETURN(_mi_pack_rec_unpack(info, &info->bit_buff, buf,
+                                  info->rec_buff, block_info.rec_len));
 panic:
   my_errno=HA_ERR_WRONG_IN_RECORD;
 err:
@@ -451,8 +454,8 @@ err:
 
 
 
-int _mi_pack_rec_unpack(register MI_INFO *info, register byte *to, byte *from,
-			ulong reclength)
+int _mi_pack_rec_unpack(register MI_INFO *info, MI_BIT_BUFF *bit_buff,
+                        register byte *to, byte *from, ulong reclength)
 {
   byte *end_field;
   reg3 MI_COLUMNDEF *end;
@@ -460,18 +463,18 @@ int _mi_pack_rec_unpack(register MI_INFO *info, register byte *to, byte *from,
   MYISAM_SHARE *share=info->s;
   DBUG_ENTER("_mi_pack_rec_unpack");
 
-  init_bit_buffer(&info->bit_buff, (uchar*) from,reclength);
+  init_bit_buffer(bit_buff, (uchar*) from, reclength);
 
   for (current_field=share->rec, end=current_field+share->base.fields ;
        current_field < end ;
        current_field++,to=end_field)
   {
     end_field=to+current_field->length;
-    (*current_field->unpack)(current_field,&info->bit_buff,(uchar*) to,
+    (*current_field->unpack)(current_field, bit_buff, (uchar*) to,
 			     (uchar*) end_field);
   }
-  if (! info->bit_buff.error &&
-      info->bit_buff.pos - info->bit_buff.bits/8 == info->bit_buff.end)
+  if (!bit_buff->error &&
+      bit_buff->pos - bit_buff->bits / 8 == bit_buff->end)
     DBUG_RETURN(0);
   info->update&= ~HA_STATE_AKTIV;
   DBUG_RETURN(my_errno=HA_ERR_WRONG_IN_RECORD);
@@ -985,13 +988,16 @@ int _mi_read_rnd_pack_record(MI_INFO *info, byte *buf,
 
   if (info->opt_flag & READ_CACHE_USED)
   {
-    if (_mi_read_cache(&info->rec_cache,(byte*) block_info.header,filepos,
-		      share->pack.ref_length, skip_deleted_blocks))
+    if (_mi_read_cache(&info->rec_cache, (byte*) block_info.header,
+                       filepos, share->pack.ref_length,
+                       skip_deleted_blocks ? READING_NEXT : 0))
       goto err;
-    b_type=_mi_pack_get_block_info(info,&block_info,-1, filepos);
+    b_type=_mi_pack_get_block_info(info, &info->bit_buff, &block_info,
+                                   &info->rec_buff, -1, filepos);
   }
   else
-    b_type=_mi_pack_get_block_info(info,&block_info,info->dfile,filepos);
+    b_type=_mi_pack_get_block_info(info, &info->bit_buff, &block_info,
+                                   &info->rec_buff, info->dfile, filepos);
   if (b_type)
     goto err;					/* Error code is already set */
 #ifndef DBUG_OFF
@@ -1004,9 +1010,9 @@ int _mi_read_rnd_pack_record(MI_INFO *info, byte *buf,
 
   if (info->opt_flag & READ_CACHE_USED)
   {
-    if (_mi_read_cache(&info->rec_cache,(byte*) info->rec_buff,
-		      block_info.filepos, block_info.rec_len,
-		      skip_deleted_blocks))
+    if (_mi_read_cache(&info->rec_cache, (byte*) info->rec_buff,
+                       block_info.filepos, block_info.rec_len,
+                       skip_deleted_blocks ? READING_NEXT : 0))
       goto err;
   }
   else
@@ -1021,8 +1027,8 @@ int _mi_read_rnd_pack_record(MI_INFO *info, byte *buf,
   info->nextpos=block_info.filepos+block_info.rec_len;
   info->update|= HA_STATE_AKTIV | HA_STATE_KEY_CHANGED;
 
-  DBUG_RETURN (_mi_pack_rec_unpack(info,buf,info->rec_buff,
-				   block_info.rec_len));
+  DBUG_RETURN (_mi_pack_rec_unpack(info, &info->bit_buff, buf,
+                                   info->rec_buff, block_info.rec_len));
  err:
   DBUG_RETURN(my_errno);
 }
@@ -1030,8 +1036,9 @@ int _mi_read_rnd_pack_record(MI_INFO *info, byte *buf,
 
 	/* Read and process header from a huff-record-file */
 
-uint _mi_pack_get_block_info(MI_INFO *myisam, MI_BLOCK_INFO *info, File file,
-			     my_off_t filepos)
+uint _mi_pack_get_block_info(MI_INFO *myisam, MI_BIT_BUFF *bit_buff,
+                             MI_BLOCK_INFO *info, byte **rec_buff_p,
+                             File file, my_off_t filepos)
 {
   uchar *header=info->header;
   uint head_length,ref_length;
@@ -1056,17 +1063,17 @@ uint _mi_pack_get_block_info(MI_INFO *myisam, MI_BLOCK_INFO *info, File file,
     head_length+= read_pack_length((uint) myisam->s->pack.version,
                                    header + head_length, &info->blob_len);
     if (!(mi_alloc_rec_buff(myisam,info->rec_len + info->blob_len,
-			    &myisam->rec_buff)))
+			    rec_buff_p)))
       return BLOCK_FATAL_ERROR;			/* not enough memory */
-    myisam->bit_buff.blob_pos=(uchar*) myisam->rec_buff+info->rec_len;
-    myisam->bit_buff.blob_end= myisam->bit_buff.blob_pos+info->blob_len;
+    bit_buff->blob_pos= (uchar*) *rec_buff_p + info->rec_len;
+    bit_buff->blob_end= bit_buff->blob_pos + info->blob_len;
     myisam->blob_length=info->blob_len;
   }
   info->filepos=filepos+head_length;
   if (file > 0)
   {
     info->offset=min(info->rec_len, ref_length - head_length);
-    memcpy(myisam->rec_buff, header+head_length, info->offset);
+    memcpy(*rec_buff_p, header + head_length, info->offset);
   }
   return 0;
 }
@@ -1206,7 +1213,8 @@ void _mi_unmap_file(MI_INFO *info)
 }
 
 
-static uchar *_mi_mempack_get_block_info(MI_INFO *myisam,MI_BLOCK_INFO *info,
+static uchar *_mi_mempack_get_block_info(MI_INFO *myisam, MI_BIT_BUFF *bit_buff,
+                                         MI_BLOCK_INFO *info, byte **rec_buff_p,
 					 uchar *header)
 {
   header+= read_pack_length((uint) myisam->s->pack.version, header,
@@ -1217,10 +1225,10 @@ static uchar *_mi_mempack_get_block_info(MI_INFO *myisam,MI_BLOCK_INFO *info,
                               &info->blob_len);
     /* mi_alloc_rec_buff sets my_errno on error */
     if (!(mi_alloc_rec_buff(myisam, info->blob_len,
-			    &myisam->rec_buff)))
+			    rec_buff_p)))
       return 0;				/* not enough memory */
-    myisam->bit_buff.blob_pos=(uchar*) myisam->rec_buff;
-    myisam->bit_buff.blob_end= (uchar*) myisam->rec_buff + info->blob_len;
+    bit_buff->blob_pos= (uchar*) *rec_buff_p;
+    bit_buff->blob_end= (uchar*) *rec_buff_p + info->blob_len;
   }
   return header;
 }
@@ -1236,11 +1244,13 @@ static int _mi_read_mempack_record(MI_INFO *info, my_off_t filepos, byte *buf)
   if (filepos == HA_OFFSET_ERROR)
     DBUG_RETURN(-1);			/* _search() didn't find record */
 
-  if (!(pos= (byte*) _mi_mempack_get_block_info(info,&block_info,
+  if (!(pos= (byte*) _mi_mempack_get_block_info(info, &info->bit_buff,
+                                                &block_info, &info->rec_buff,
 						(uchar*) share->file_map+
 						filepos)))
     DBUG_RETURN(-1);
-  DBUG_RETURN(_mi_pack_rec_unpack(info, buf, pos, block_info.rec_len));
+  DBUG_RETURN(_mi_pack_rec_unpack(info, &info->bit_buff, buf,
+                                  pos, block_info.rec_len));
 }
 
 
@@ -1260,7 +1270,8 @@ static int _mi_read_rnd_mempack_record(MI_INFO *info, byte *buf,
     my_errno=HA_ERR_END_OF_FILE;
     goto err;
   }
-  if (!(pos= (byte*) _mi_mempack_get_block_info(info,&block_info,
+  if (!(pos= (byte*) _mi_mempack_get_block_info(info, &info->bit_buff,
+                                                &block_info, &info->rec_buff,
 						(uchar*)
 						(start=share->file_map+
 						 filepos))))
@@ -1277,7 +1288,8 @@ static int _mi_read_rnd_mempack_record(MI_INFO *info, byte *buf,
   info->nextpos=filepos+(uint) (pos-start)+block_info.rec_len;
   info->update|= HA_STATE_AKTIV | HA_STATE_KEY_CHANGED;
 
-  DBUG_RETURN (_mi_pack_rec_unpack(info,buf,pos, block_info.rec_len));
+  DBUG_RETURN (_mi_pack_rec_unpack(info, &info->bit_buff, buf,
+                                   pos, block_info.rec_len));
  err:
   DBUG_RETURN(my_errno);
 }
diff --git a/myisam/myisamdef.h b/myisam/myisamdef.h
index a766d59d72a..6365f0e1b0c 100644
--- a/myisam/myisamdef.h
+++ b/myisam/myisamdef.h
@@ -75,7 +75,7 @@ typedef struct st_mi_state_info
   ulong sec_index_changed;		/* Updated when new sec_index */
   ulong sec_index_used;			/* which extra index are in use */
   ulonglong key_map;			/* Which keys are in use */
-  ha_checksum checksum;
+  ha_checksum checksum;                 /* Table checksum */
   ulong version;			/* timestamp of create */
   time_t create_time;			/* Time when created database */
   time_t recover_time;			/* Time for last recover */
@@ -176,6 +176,7 @@ typedef struct st_mi_isam_share {	/* Shared between opens */
   int (*delete_record)(struct st_myisam_info*);
   int (*read_rnd)(struct st_myisam_info*, byte*, my_off_t, my_bool);
   int (*compare_record)(struct st_myisam_info*, const byte *);
+  /* Function to use for a row checksum. */
   ha_checksum (*calc_checksum)(struct st_myisam_info*, const byte *);
   int (*compare_unique)(struct st_myisam_info*, MI_UNIQUEDEF *,
 			const byte *record, my_off_t pos);
@@ -249,7 +250,7 @@ struct st_myisam_info {
   my_off_t last_keypage;		/* Last key page read */
   my_off_t last_search_keypage;		/* Last keypage when searching */
   my_off_t dupp_key_pos;
-  ha_checksum checksum;
+  ha_checksum checksum;                 /* Temp storage for row checksum */
   /* QQ: the folloing two xxx_length fields should be removed,
      as they are not compatible with parallel repair */
   ulong packed_length,blob_length;	/* Length of found, packed record */
@@ -297,8 +298,9 @@ typedef struct st_mi_sort_param
   pthread_t  thr;
   IO_CACHE read_cache, tempfile, tempfile_for_exceptions;
   DYNAMIC_ARRAY buffpek;
-  
-  /* 
+  MI_BIT_BUFF   bit_buff;               /* For parallel repair of packrec. */
+
+  /*
     The next two are used to collect statistics, see update_key_parts for
     description.
   */
@@ -309,6 +311,7 @@ typedef struct st_mi_sort_param
   uint key, key_length,real_key_length,sortbuff_size;
   uint maxbuffers, keys, find_length, sort_keys_length;
   my_bool fix_datafile, master;
+  my_bool calc_checksum;                /* calculate table checksum */
   MI_KEYDEF *keyinfo;
   HA_KEYSEG *seg;
   SORT_INFO *sort_info;
@@ -361,8 +364,15 @@ typedef struct st_mi_sort_param
 #define mi_putint(x,y,nod) { uint16 boh=(nod ? (uint16) 32768 : 0) + (uint16) (y);\
 			  mi_int2store(x,boh); }
 #define mi_test_if_nod(x) (x[0] & 128 ? info->s->base.key_reflength : 0)
-#define mi_mark_crashed(x) (x)->s->state.changed|=STATE_CRASHED
-#define mi_mark_crashed_on_repair(x) { (x)->s->state.changed|=STATE_CRASHED|STATE_CRASHED_ON_REPAIR ; (x)->update|= HA_STATE_CHANGED; }
+#define mi_mark_crashed(x) do{(x)->s->state.changed|= STATE_CRASHED; \
+                              DBUG_PRINT("error", ("Marked table crashed")); \
+                           }while(0)
+#define mi_mark_crashed_on_repair(x) do{(x)->s->state.changed|= \
+                                        STATE_CRASHED|STATE_CRASHED_ON_REPAIR; \
+                                        (x)->update|= HA_STATE_CHANGED; \
+                                        DBUG_PRINT("error", \
+                                                   ("Marked table crashed")); \
+                                     }while(0)
 #define mi_is_crashed(x) ((x)->s->state.changed & STATE_CRASHED)
 #define mi_is_crashed_on_repair(x) ((x)->s->state.changed & STATE_CRASHED_ON_REPAIR)
 
@@ -600,8 +610,8 @@ extern void _mi_print_key(FILE *stream,HA_KEYSEG *keyseg,const uchar *key,
 extern my_bool _mi_read_pack_info(MI_INFO *info,pbool fix_keys);
 extern int _mi_read_pack_record(MI_INFO *info,my_off_t filepos,byte *buf);
 extern int _mi_read_rnd_pack_record(MI_INFO*, byte *,my_off_t, my_bool);
-extern int _mi_pack_rec_unpack(MI_INFO *info,byte *to,byte *from,
-			       ulong reclength);
+extern int _mi_pack_rec_unpack(MI_INFO *info, MI_BIT_BUFF *bit_buff,
+                               byte *to, byte *from, ulong reclength);
 extern ulonglong mi_safe_mul(ulonglong a,ulonglong b);
 extern int _mi_ft_update(MI_INFO *info, uint keynr, byte *keybuf,
 			 const byte *oldrec, const byte *newrec, my_off_t pos);
@@ -666,7 +676,9 @@ extern "C" {
 
 extern uint _mi_get_block_info(MI_BLOCK_INFO *,File, my_off_t);
 extern uint _mi_rec_pack(MI_INFO *info,byte *to,const byte *from);
-extern uint _mi_pack_get_block_info(MI_INFO *, MI_BLOCK_INFO *, File, my_off_t);
+extern uint _mi_pack_get_block_info(MI_INFO *myisam, MI_BIT_BUFF *bit_buff,
+                                    MI_BLOCK_INFO *info, byte **rec_buff_p,
+                                    File file, my_off_t filepos);
 extern void _my_store_blob_length(byte *pos,uint pack_length,uint length);
 extern void _myisam_log(enum myisam_log_commands command,MI_INFO *info,
 		       const byte *buffert,uint length);
diff --git a/myisam/sort.c b/myisam/sort.c
index 1a3dc147cd9..727840709da 100644
--- a/myisam/sort.c
+++ b/myisam/sort.c
@@ -309,7 +309,7 @@ static ha_rows NEAR_F find_all_keys(MI_SORT_PARAM *info, uint keys,
 
 pthread_handler_decl(thr_find_all_keys,arg)
 {
-  MI_SORT_PARAM *info= (MI_SORT_PARAM*) arg;
+  MI_SORT_PARAM *sort_param= (MI_SORT_PARAM*) arg;
   int error;
   uint memavl,old_memavl,keys,sort_length;
   uint idx, maxbuffer;
@@ -321,32 +321,34 @@ pthread_handler_decl(thr_find_all_keys,arg)
 
   if (my_thread_init())
     goto err;
-  if (info->sort_info->got_error)
+  DBUG_ENTER("thr_find_all_keys");
+  DBUG_PRINT("enter", ("master: %d", sort_param->master));
+  if (sort_param->sort_info->got_error)
     goto err;
 
-  if (info->keyinfo->flag && HA_VAR_LENGTH_KEY)
+  if (sort_param->keyinfo->flag && HA_VAR_LENGTH_KEY)
   {
-    info->write_keys=write_keys_varlen;
-    info->read_to_buffer=read_to_buffer_varlen;
-    info->write_key=write_merge_key_varlen;
+    sort_param->write_keys=     write_keys_varlen;
+    sort_param->read_to_buffer= read_to_buffer_varlen;
+    sort_param->write_key=      write_merge_key_varlen;
   }
   else
   {
-    info->write_keys=write_keys;
-    info->read_to_buffer=read_to_buffer;
-    info->write_key=write_merge_key;
+    sort_param->write_keys=     write_keys;
+    sort_param->read_to_buffer= read_to_buffer;
+    sort_param->write_key=      write_merge_key;
   }
 
-  my_b_clear(&info->tempfile);
-  my_b_clear(&info->tempfile_for_exceptions);
-  bzero((char*) &info->buffpek,sizeof(info->buffpek));
-  bzero((char*) &info->unique, sizeof(info->unique));
+  my_b_clear(&sort_param->tempfile);
+  my_b_clear(&sort_param->tempfile_for_exceptions);
+  bzero((char*) &sort_param->buffpek, sizeof(sort_param->buffpek));
+  bzero((char*) &sort_param->unique,  sizeof(sort_param->unique));
   sort_keys= (uchar **) NULL;
 
-  memavl=max(info->sortbuff_size, MIN_SORT_MEMORY);
-  idx=      info->sort_info->max_records;
-  sort_length=  info->key_length;
-  maxbuffer= 1;
+  memavl=       max(sort_param->sortbuff_size, MIN_SORT_MEMORY);
+  idx=          sort_param->sort_info->max_records;
+  sort_length=  sort_param->key_length;
+  maxbuffer=    1;
 
   while (memavl >= MIN_SORT_MEMORY)
   {
@@ -363,18 +365,19 @@ pthread_handler_decl(thr_find_all_keys,arg)
             (keys=(memavl-sizeof(BUFFPEK)*maxbuffer)/
              (sort_length+sizeof(char*))) <= 1)
         {
-          mi_check_print_error(info->sort_info->param,
+          mi_check_print_error(sort_param->sort_info->param,
                                "sort_buffer_size is to small");
           goto err;
         }
       }
       while ((maxbuffer= (int) (idx/(keys-1)+1)) != skr);
     }
-    if ((sort_keys=(uchar **)my_malloc(keys*(sort_length+sizeof(char*))+
-				       ((info->keyinfo->flag & HA_FULLTEXT) ?
-					HA_FT_MAXBYTELEN : 0), MYF(0))))
+    if ((sort_keys= (uchar**)
+         my_malloc(keys*(sort_length+sizeof(char*))+
+                   ((sort_param->keyinfo->flag & HA_FULLTEXT) ?
+                    HA_FT_MAXBYTELEN : 0), MYF(0))))
     {
-      if (my_init_dynamic_array(&info->buffpek, sizeof(BUFFPEK),
+      if (my_init_dynamic_array(&sort_param->buffpek, sizeof(BUFFPEK),
 				maxbuffer, maxbuffer/2))
         my_free((gptr) sort_keys,MYF(0));
       else
@@ -386,69 +389,87 @@ pthread_handler_decl(thr_find_all_keys,arg)
   }
   if (memavl < MIN_SORT_MEMORY)
   {
-    mi_check_print_error(info->sort_info->param,"Sort buffer to small"); /* purecov: tested */
+    mi_check_print_error(sort_param->sort_info->param, "Sort buffer too small");
     goto err; /* purecov: tested */
   }
 
-  if (info->sort_info->param->testflag & T_VERBOSE)
-    printf("Key %d - Allocating buffer for %d keys\n",info->key+1,keys);
-  info->sort_keys=sort_keys;
+  if (sort_param->sort_info->param->testflag & T_VERBOSE)
+    printf("Key %d - Allocating buffer for %d keys\n",
+           sort_param->key + 1, keys);
+  sort_param->sort_keys= sort_keys;
 
   idx=error=0;
   sort_keys[0]=(uchar*) (sort_keys+keys);
 
-  while (!(error=info->sort_info->got_error) &&
-         !(error=(*info->key_read)(info,sort_keys[idx])))
+  DBUG_PRINT("info", ("reading keys"));
+  while (!(error= sort_param->sort_info->got_error) &&
+         !(error= (*sort_param->key_read)(sort_param, sort_keys[idx])))
   {
-    if (info->real_key_length > info->key_length)
+    if (sort_param->real_key_length > sort_param->key_length)
     {
-      if (write_key(info,sort_keys[idx], &info->tempfile_for_exceptions))
+      if (write_key(sort_param, sort_keys[idx],
+                    &sort_param->tempfile_for_exceptions))
         goto err;
       continue;
     }
 
     if (++idx == keys)
     {
-      if (info->write_keys(info,sort_keys,idx-1,
-		     (BUFFPEK *)alloc_dynamic(&info->buffpek),
-		     &info->tempfile))
+      if (sort_param->write_keys(sort_param, sort_keys, idx - 1,
+                                 (BUFFPEK*) alloc_dynamic(&sort_param->buffpek),
+                                 &sort_param->tempfile))
         goto err;
       sort_keys[0]=(uchar*) (sort_keys+keys);
-      memcpy(sort_keys[0],sort_keys[idx-1],(size_t) info->key_length);
+      memcpy(sort_keys[0], sort_keys[idx - 1], (size_t) sort_param->key_length);
       idx=1;
     }
-    sort_keys[idx]=sort_keys[idx-1]+info->key_length;
+    sort_keys[idx]= sort_keys[idx - 1] + sort_param->key_length;
   }
   if (error > 0)
     goto err;
-  if (info->buffpek.elements)
+  if (sort_param->buffpek.elements)
   {
-    if (info->write_keys(info,sort_keys, idx,
-		   (BUFFPEK *) alloc_dynamic(&info->buffpek), &info->tempfile))
+    if (sort_param->write_keys(sort_param, sort_keys, idx,
+                               (BUFFPEK*) alloc_dynamic(&sort_param->buffpek),
+                               &sort_param->tempfile))
       goto err;
-    info->keys=(info->buffpek.elements-1)*(keys-1)+idx;
+    sort_param->keys= (sort_param->buffpek.elements - 1) * (keys - 1) + idx;
   }
   else
-    info->keys=idx;
+    sort_param->keys= idx;
 
-  info->sort_keys_length=keys;
+  sort_param->sort_keys_length= keys;
   goto ok;
 
 err:
-  info->sort_info->got_error=1; /* no need to protect this with a mutex */
+  DBUG_PRINT("error", ("got some error"));
+  sort_param->sort_info->got_error= 1; /* no need to protect with a mutex */
   if (sort_keys)
     my_free((gptr) sort_keys,MYF(0));
-  info->sort_keys=0;
-  delete_dynamic(& info->buffpek);
-  close_cached_file(&info->tempfile);
-  close_cached_file(&info->tempfile_for_exceptions);
+  sort_param->sort_keys= 0;
+  delete_dynamic(& sort_param->buffpek);
+  close_cached_file(&sort_param->tempfile);
+  close_cached_file(&sort_param->tempfile_for_exceptions);
 
 ok:
-  remove_io_thread(&info->read_cache);
-  pthread_mutex_lock(&info->sort_info->mutex);
-  info->sort_info->threads_running--;
-  pthread_cond_signal(&info->sort_info->cond);
-  pthread_mutex_unlock(&info->sort_info->mutex);
+  /*
+    Detach from the share if the writer is involved. Avoid others to
+    be blocked. This includes a flush of the write buffer. This will
+    also indicate EOF to the readers.
+  */
+  if (sort_param->sort_info->info->rec_cache.share)
+    remove_io_thread(&sort_param->sort_info->info->rec_cache);
+
+  /* Readers detach from the share if any. Avoid others to be blocked. */
+  if (sort_param->read_cache.share)
+    remove_io_thread(&sort_param->read_cache);
+
+  pthread_mutex_lock(&sort_param->sort_info->mutex);
+  if (!--sort_param->sort_info->threads_running)
+    pthread_cond_signal(&sort_param->sort_info->cond);
+  pthread_mutex_unlock(&sort_param->sort_info->mutex);
+
+  DBUG_PRINT("exit", ("======== ending thread ========"));
   my_thread_end();
   return NULL;
 }
@@ -466,6 +487,7 @@ int thr_write_keys(MI_SORT_PARAM *sort_param)
   MYISAM_SHARE *share=info->s;
   MI_SORT_PARAM *sinfo;
   byte *mergebuf=0;
+  DBUG_ENTER("thr_write_keys");
   LINT_INIT(length);
 
   for (i= 0, sinfo= sort_param ;
@@ -602,7 +624,7 @@ int thr_write_keys(MI_SORT_PARAM *sort_param)
     }
   }
   my_free((gptr) mergebuf,MYF(MY_ALLOW_ZERO_PTR));
-  return got_error;
+  DBUG_RETURN(got_error);
 }
 #endif /* THREAD */
 
diff --git a/mysql-test/r/myisam.result b/mysql-test/r/myisam.result
index 05f72b22ed1..b34c127595f 100644
--- a/mysql-test/r/myisam.result
+++ b/mysql-test/r/myisam.result
@@ -797,6 +797,132 @@ a	b
 xxxxxxxxx	bbbbbb
 xxxxxxxxx	bbbbbb
 DROP TABLE t1;
+SET @@myisam_repair_threads=2;
+SHOW VARIABLES LIKE 'myisam_repair%';
+Variable_name	Value
+myisam_repair_threads	2
+CREATE TABLE t1 (
+`_id` int(11) NOT NULL default '0',
+`url` text,
+`email` text,
+`description` text,
+`loverlap` int(11) default NULL,
+`roverlap` int(11) default NULL,
+`lneighbor_id` int(11) default NULL,
+`rneighbor_id` int(11) default NULL,
+`length_` int(11) default NULL,
+`sequence` mediumtext,
+`name` text,
+`_obj_class` text NOT NULL,
+PRIMARY KEY  (`_id`),
+UNIQUE KEY `sequence_name_index` (`name`(50)),
+KEY (`length_`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1;
+INSERT INTO t1 VALUES
+(1,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample1',''),
+(2,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample2',''),
+(3,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample3',''),
+(4,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample4',''),
+(5,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample5',''),
+(6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample6',''),
+(7,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample7',''),
+(8,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample8',''),
+(9,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample9','');
+SELECT _id FROM t1;
+_id
+1
+2
+3
+4
+5
+6
+7
+8
+9
+DELETE FROM t1 WHERE _id < 8;
+SHOW TABLE STATUS LIKE 't1';
+Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment
+t1	MyISAM	9	Dynamic	2	#	#	#	#	140	#	#	#	#	#	#		
+CHECK TABLE t1 EXTENDED;
+Table	Op	Msg_type	Msg_text
+test.t1	check	status	OK
+OPTIMIZE TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	optimize	status	OK
+CHECK TABLE t1 EXTENDED;
+Table	Op	Msg_type	Msg_text
+test.t1	check	status	OK
+SHOW TABLE STATUS LIKE 't1';
+Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment
+t1	MyISAM	9	Dynamic	2	#	#	#	#	0	#	#	#	#	#	#		
+SELECT _id FROM t1;
+_id
+8
+9
+DROP TABLE t1;
+CREATE TABLE t1 (
+`_id` int(11) NOT NULL default '0',
+`url` text,
+`email` text,
+`description` text,
+`loverlap` int(11) default NULL,
+`roverlap` int(11) default NULL,
+`lneighbor_id` int(11) default NULL,
+`rneighbor_id` int(11) default NULL,
+`length_` int(11) default NULL,
+`sequence` mediumtext,
+`name` text,
+`_obj_class` text NOT NULL,
+PRIMARY KEY  (`_id`),
+UNIQUE KEY `sequence_name_index` (`name`(50)),
+KEY (`length_`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1;
+INSERT INTO t1 VALUES
+(1,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample1',''),
+(2,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample2',''),
+(3,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample3',''),
+(4,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample4',''),
+(5,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample5',''),
+(6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample6',''),
+(7,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample7',''),
+(8,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample8',''),
+(9,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample9','');
+SELECT _id FROM t1;
+_id
+1
+2
+3
+4
+5
+6
+7
+8
+9
+DELETE FROM t1 WHERE _id < 8;
+SHOW TABLE STATUS LIKE 't1';
+Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment
+t1	MyISAM	9	Dynamic	2	#	#	#	#	140	#	#	#	#	#	#		
+CHECK TABLE t1 EXTENDED;
+Table	Op	Msg_type	Msg_text
+test.t1	check	status	OK
+REPAIR TABLE t1 QUICK;
+Table	Op	Msg_type	Msg_text
+test.t1	repair	status	OK
+CHECK TABLE t1 EXTENDED;
+Table	Op	Msg_type	Msg_text
+test.t1	check	status	OK
+SHOW TABLE STATUS LIKE 't1';
+Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment
+t1	MyISAM	9	Dynamic	2	#	#	#	#	140	#	#	#	#	#	#		
+SELECT _id FROM t1;
+_id
+8
+9
+DROP TABLE t1;
+SET @@myisam_repair_threads=1;
+SHOW VARIABLES LIKE 'myisam_repair%';
+Variable_name	Value
+myisam_repair_threads	1
 show create table t1;
 Table	Create Table
 t1	CREATE TEMPORARY TABLE `t1` (
diff --git a/mysql-test/t/myisam.test b/mysql-test/t/myisam.test
index a62a6487882..745e3a2e377 100644
--- a/mysql-test/t/myisam.test
+++ b/mysql-test/t/myisam.test
@@ -763,6 +763,97 @@ SELECT * FROM t1;
 DROP TABLE t1;
 
 #
+# Bug#8283 - OPTIMIZE TABLE causes data loss
+#
+SET @@myisam_repair_threads=2;
+SHOW VARIABLES LIKE 'myisam_repair%';
+#
+# Test OPTIMIZE. This creates a new data file.
+CREATE TABLE t1 (
+  `_id` int(11) NOT NULL default '0',
+  `url` text,
+  `email` text,
+  `description` text,
+  `loverlap` int(11) default NULL,
+  `roverlap` int(11) default NULL,
+  `lneighbor_id` int(11) default NULL,
+  `rneighbor_id` int(11) default NULL,
+  `length_` int(11) default NULL,
+  `sequence` mediumtext,
+  `name` text,
+  `_obj_class` text NOT NULL,
+  PRIMARY KEY  (`_id`),
+  UNIQUE KEY `sequence_name_index` (`name`(50)),
+  KEY (`length_`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1;
+#
+INSERT INTO t1 VALUES
+  (1,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample1',''),
+  (2,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample2',''),
+  (3,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample3',''),
+  (4,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample4',''),
+  (5,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample5',''),
+  (6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample6',''),
+  (7,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample7',''),
+  (8,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample8',''),
+  (9,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample9','');
+#
+SELECT _id FROM t1;
+DELETE FROM t1 WHERE _id < 8;
+--replace_column 6 # 7 # 8 # 9 # 11 # 12 # 13 # 14 # 15 # 16 #
+SHOW TABLE STATUS LIKE 't1';
+CHECK TABLE t1 EXTENDED;
+OPTIMIZE TABLE t1;
+CHECK TABLE t1 EXTENDED;
+--replace_column 6 # 7 # 8 # 9 # 11 # 12 # 13 # 14 # 15 # 16 #
+SHOW TABLE STATUS LIKE 't1';
+SELECT _id FROM t1;
+DROP TABLE t1;
+#
+# Test REPAIR QUICK. This retains the old data file.
+CREATE TABLE t1 (
+  `_id` int(11) NOT NULL default '0',
+  `url` text,
+  `email` text,
+  `description` text,
+  `loverlap` int(11) default NULL,
+  `roverlap` int(11) default NULL,
+  `lneighbor_id` int(11) default NULL,
+  `rneighbor_id` int(11) default NULL,
+  `length_` int(11) default NULL,
+  `sequence` mediumtext,
+  `name` text,
+  `_obj_class` text NOT NULL,
+  PRIMARY KEY  (`_id`),
+  UNIQUE KEY `sequence_name_index` (`name`(50)),
+  KEY (`length_`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1;
+#
+INSERT INTO t1 VALUES
+  (1,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample1',''),
+  (2,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample2',''),
+  (3,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample3',''),
+  (4,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample4',''),
+  (5,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample5',''),
+  (6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample6',''),
+  (7,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample7',''),
+  (8,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample8',''),
+  (9,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'sample9','');
+#
+SELECT _id FROM t1;
+DELETE FROM t1 WHERE _id < 8;
+--replace_column 6 # 7 # 8 # 9 # 11 # 12 # 13 # 14 # 15 # 16 #
+SHOW TABLE STATUS LIKE 't1';
+CHECK TABLE t1 EXTENDED;
+REPAIR TABLE t1 QUICK;
+CHECK TABLE t1 EXTENDED;
+--replace_column 6 # 7 # 8 # 9 # 11 # 12 # 13 # 14 # 15 # 16 #
+SHOW TABLE STATUS LIKE 't1';
+SELECT _id FROM t1;
+DROP TABLE t1;
+#
+SET @@myisam_repair_threads=1;
+SHOW VARIABLES LIKE 'myisam_repair%';
 # Bug#8706 - temporary table with data directory option fails
 #
 connect (session1,localhost,root,,);
diff --git a/mysys/mf_iocache.c b/mysys/mf_iocache.c
index 0007784c2b2..58d4756b702 100644
--- a/mysys/mf_iocache.c
+++ b/mysys/mf_iocache.c
@@ -70,7 +70,6 @@ static void my_aiowait(my_aio_result *result);
 #define IO_ROUND_UP(X) (((X)+IO_SIZE-1) & ~(IO_SIZE-1))
 #define IO_ROUND_DN(X) ( (X)            & ~(IO_SIZE-1))
 
-
 /*
   Setup internal pointers inside IO_CACHE
 
@@ -500,65 +499,366 @@ int _my_b_read(register IO_CACHE *info, byte *Buffer, uint Count)
   DBUG_RETURN(0);
 }
 
+
 #ifdef THREAD
-/* Prepare IO_CACHE for shared use */
-void init_io_cache_share(IO_CACHE *info, IO_CACHE_SHARE *s, uint num_threads)
+/*
+  Prepare IO_CACHE for shared use.
+
+  SYNOPSIS
+    init_io_cache_share()
+      read_cache                A read cache. This will be copied for
+                                every thread after setup.
+      cshare                    The share.
+      write_cache               If non-NULL a write cache that is to be
+                                synchronized with the read caches.
+      num_threads               Number of threads sharing the cache
+                                including the write thread if any.
+
+  DESCRIPTION
+
+    The shared cache is used so: One IO_CACHE is initialized with
+    init_io_cache(). This includes the allocation of a buffer. Then a
+    share is allocated and init_io_cache_share() is called with the io
+    cache and the share. Then the io cache is copied for each thread. So
+    every thread has its own copy of IO_CACHE. But the allocated buffer
+    is shared because cache->buffer is the same for all caches.
+
+    One thread reads data from the file into the buffer. All threads
+    read from the buffer, but every thread maintains its own set of
+    pointers into the buffer. When all threads have used up the buffer
+    contents, one of the threads reads the next block of data into the
+    buffer. To accomplish this, each thread enters the cache lock before
+    accessing the buffer. They wait in lock_io_cache() until all threads
+    joined the lock. The last thread entering the lock is in charge of
+    reading from file to buffer. It wakes all threads when done.
+
+    Synchronizing a write cache to the read caches works so: Whenever
+    the write buffer needs a flush, the write thread enters the lock and
+    waits for all other threads to enter the lock too. They do this when
+    they have used up the read buffer. When all threads are in the lock,
+    the write thread copies the write buffer to the read buffer and
+    wakes all threads.
+
+    share->running_threads is the number of threads not being in the
+    cache lock. When entering lock_io_cache() the number is decreased.
+    When the thread that fills the buffer enters unlock_io_cache() the
+    number is reset to the number of threads. The condition
+    running_threads == 0 means that all threads are in the lock. Bumping
+    up the number to the full count is non-intuitive. But increasing the
+    number by one for each thread that leaves the lock could lead to a
+    solo run of one thread. The last thread to join a lock reads from
+    file to buffer, wakes the other threads, processes the data in the
+    cache and enters the lock again. If no other thread left the lock
+    meanwhile, it would think it's the last one again and read the next
+    block...
+
+    The share has copies of 'error', 'buffer', 'read_end', and
+    'pos_in_file' from the thread that filled the buffer. We may not be
+    able to access this information directly from its cache because the
+    thread may be removed from the share before the variables could be
+    copied by all other threads. Or, if a write buffer is synchronized,
+    it would change its 'pos_in_file' after waking the other threads,
+    possibly before they could copy its value.
+
+    However, the 'buffer' variable in the share is for a synchronized
+    write cache. It needs to know where to put the data. Otherwise it
+    would need access to the read cache of one of the threads that is
+    not yet removed from the share.
+
+  RETURN
+    void
+*/
+
+void init_io_cache_share(IO_CACHE *read_cache, IO_CACHE_SHARE *cshare,
+                         IO_CACHE *write_cache, uint num_threads)
 {
-  DBUG_ASSERT(info->type == READ_CACHE);
-  pthread_mutex_init(&s->mutex, MY_MUTEX_INIT_FAST);
-  pthread_cond_init (&s->cond, 0);
-  s->total=s->count=num_threads-1;
-  s->active=0;
-  info->share=s;
-  info->read_function=_my_b_read_r;
-  info->current_pos= info->current_end= 0;
+  DBUG_ENTER("init_io_cache_share");
+  DBUG_PRINT("io_cache_share", ("read_cache: 0x%lx  share: 0x%lx  "
+                                "write_cache: 0x%lx  threads: %u",
+                                read_cache, cshare, write_cache, num_threads));
+
+  DBUG_ASSERT(num_threads > 1);
+  DBUG_ASSERT(read_cache->type == READ_CACHE);
+  DBUG_ASSERT(!write_cache || (write_cache->type == WRITE_CACHE));
+
+  pthread_mutex_init(&cshare->mutex, MY_MUTEX_INIT_FAST);
+  pthread_cond_init(&cshare->cond, 0);
+  pthread_cond_init(&cshare->cond_writer, 0);
+
+  cshare->running_threads= num_threads;
+  cshare->total_threads=   num_threads;
+  cshare->error=           0;    /* Initialize. */
+  cshare->buffer=          read_cache->buffer;
+  cshare->read_end=        NULL; /* See function comment of lock_io_cache(). */
+  cshare->pos_in_file=     0;    /* See function comment of lock_io_cache(). */
+  cshare->source_cache=    write_cache; /* Can be NULL. */
+
+  read_cache->share=         cshare;
+  read_cache->read_function= _my_b_read_r;
+  read_cache->current_pos=   NULL;
+  read_cache->current_end=   NULL;
+
+  if (write_cache)
+    write_cache->share= cshare;
+
+  DBUG_VOID_RETURN;
 }
 
+
 /*
-  Remove a thread from shared access to IO_CACHE
-  Every thread should do that on exit for not
-  to deadlock other threads
+  Remove a thread from shared access to IO_CACHE.
+
+  SYNOPSIS
+    remove_io_thread()
+      cache                     The IO_CACHE to be removed from the share.
+
+  NOTE
+
+    Every thread must do that on exit for not to deadlock other threads.
+
+    The last thread destroys the pthread resources.
+
+    A writer flushes its cache first.
+
+  RETURN
+    void
 */
-void remove_io_thread(IO_CACHE *info)
+
+void remove_io_thread(IO_CACHE *cache)
 {
-  IO_CACHE_SHARE *s=info->share;
+  IO_CACHE_SHARE *cshare= cache->share;
+  uint total;
+  DBUG_ENTER("remove_io_thread");
+
+  /* If the writer goes, it needs to flush the write cache. */
+  if (cache == cshare->source_cache)
+    flush_io_cache(cache);
 
-  pthread_mutex_lock(&s->mutex);
-  s->total--;
-  if (! s->count--)
-    pthread_cond_signal(&s->cond);
-  pthread_mutex_unlock(&s->mutex);
+  pthread_mutex_lock(&cshare->mutex);
+  DBUG_PRINT("io_cache_share", ("%s: 0x%lx",
+                                (cache == cshare->source_cache) ?
+                                "writer" : "reader", cache));
+
+  /* Remove from share. */
+  total= --cshare->total_threads;
+  DBUG_PRINT("io_cache_share", ("remaining threads: %u", total));
+
+  /* Detach from share. */
+  cache->share= NULL;
+
+  /* If the writer goes, let the readers know. */
+  if (cache == cshare->source_cache)
+  {
+    DBUG_PRINT("io_cache_share", ("writer leaves"));
+    cshare->source_cache= NULL;
+  }
+
+  /* If all threads are waiting for me to join the lock, wake them. */
+  if (!--cshare->running_threads)
+  {
+    DBUG_PRINT("io_cache_share", ("the last running thread leaves, wake all"));
+    pthread_cond_signal(&cshare->cond_writer);
+    pthread_cond_broadcast(&cshare->cond);
+  }
+
+  pthread_mutex_unlock(&cshare->mutex);
+
+  if (!total)
+  {
+    DBUG_PRINT("io_cache_share", ("last thread removed, destroy share"));
+    pthread_cond_destroy (&cshare->cond_writer);
+    pthread_cond_destroy (&cshare->cond);
+    pthread_mutex_destroy(&cshare->mutex);
+  }
+
+  DBUG_VOID_RETURN;
 }
 
-static int lock_io_cache(IO_CACHE *info, my_off_t pos)
-{
-  int total;
-  IO_CACHE_SHARE *s=info->share;
 
-  pthread_mutex_lock(&s->mutex);
-  if (!s->count)
+/*
+  Lock IO cache and wait for all other threads to join.
+
+  SYNOPSIS
+    lock_io_cache()
+      cache                     The cache of the thread entering the lock.
+      pos                       File position of the block to read.
+                                Unused for the write thread.
+
+  DESCRIPTION
+
+    Wait for all threads to finish with the current buffer. We want
+    all threads to proceed in concert. The last thread to join
+    lock_io_cache() will read the block from file and all threads start
+    to use it. Then they will join again for reading the next block.
+
+    The waiting threads detect a fresh buffer by comparing
+    cshare->pos_in_file with the position they want to process next.
+    Since the first block may start at position 0, we take
+    cshare->read_end as an additional condition. This variable is
+    initialized to NULL and will be set after a block of data is written
+    to the buffer.
+
+  RETURN
+    1           OK, lock in place, go ahead and read.
+    0           OK, unlocked, another thread did the read.
+*/
+
+static int lock_io_cache(IO_CACHE *cache, my_off_t pos)
+{
+  IO_CACHE_SHARE *cshare= cache->share;
+  DBUG_ENTER("lock_io_cache");
+
+  /* Enter the lock. */
+  pthread_mutex_lock(&cshare->mutex);
+  cshare->running_threads--;
+  DBUG_PRINT("io_cache_share", ("%s: 0x%lx  pos: %lu  running: %u",
+                                (cache == cshare->source_cache) ?
+                                "writer" : "reader", cache, (ulong) pos,
+                                cshare->running_threads));
+
+  if (cshare->source_cache)
   {
-    s->count=s->total;
-    return 1;
+    /* A write cache is synchronized to the read caches. */
+
+    if (cache == cshare->source_cache)
+    {
+      /* The writer waits until all readers are here. */
+      while (cshare->running_threads)
+      {
+        DBUG_PRINT("io_cache_share", ("writer waits in lock"));
+        pthread_cond_wait(&cshare->cond_writer, &cshare->mutex);
+      }
+      DBUG_PRINT("io_cache_share", ("writer awoke, going to copy"));
+
+      /* Stay locked. Leave the lock later by unlock_io_cache(). */
+      DBUG_RETURN(1);
+    }
+
+    /* The last thread wakes the writer. */
+    if (!cshare->running_threads)
+    {
+      DBUG_PRINT("io_cache_share", ("waking writer"));
+      pthread_cond_signal(&cshare->cond_writer);
+    }
+
+    /*
+      Readers wait until the data is copied from the writer. Another
+      reason to stop waiting is the removal of the write thread. If this
+      happens, we leave the lock with old data in the buffer.
+    */
+    while ((!cshare->read_end || (cshare->pos_in_file < pos)) &&
+           cshare->source_cache)
+    {
+      DBUG_PRINT("io_cache_share", ("reader waits in lock"));
+      pthread_cond_wait(&cshare->cond, &cshare->mutex);
+    }
+
+    /*
+      If the writer was removed from the share while this thread was
+      asleep, we need to simulate an EOF condition. The writer cannot
+      reset the share variables as they might still be in use by readers
+      of the last block. When we awake here then because the last
+      joining thread signalled us. If the writer is not the last, it
+      will not signal. So it is safe to clear the buffer here.
+    */
+    if (!cshare->read_end || (cshare->pos_in_file < pos))
+    {
+      DBUG_PRINT("io_cache_share", ("reader found writer removed. EOF"));
+      cshare->read_end= cshare->buffer; /* Empty buffer. */
+      cshare->error= 0; /* EOF is not an error. */
+    }
   }
+  else
+  {
+    /*
+      There are read caches only. The last thread arriving in
+      lock_io_cache() continues with a locked cache and reads the block.
+    */
+    if (!cshare->running_threads)
+    {
+      DBUG_PRINT("io_cache_share", ("last thread joined, going to read"));
+      /* Stay locked. Leave the lock later by unlock_io_cache(). */
+      DBUG_RETURN(1);
+    }
 
-  total=s->total;
-  s->count--;
-  while (!s->active || s->active->pos_in_file < pos)
-    pthread_cond_wait(&s->cond, &s->mutex);
+    /*
+      All other threads wait until the requested block is read by the
+      last thread arriving. Another reason to stop waiting is the
+      removal of a thread. If this leads to all threads being in the
+      lock, we have to continue also. The first of the awaken threads
+      will then do the read.
+    */
+    while ((!cshare->read_end || (cshare->pos_in_file < pos)) &&
+           cshare->running_threads)
+    {
+      DBUG_PRINT("io_cache_share", ("reader waits in lock"));
+      pthread_cond_wait(&cshare->cond, &cshare->mutex);
+    }
 
-  if (s->total < total &&
-      (!s->active || s->active->pos_in_file < pos))
-    return 1;
+    /* If the block is not yet read, continue with a locked cache and read. */
+    if (!cshare->read_end || (cshare->pos_in_file < pos))
+    {
+      DBUG_PRINT("io_cache_share", ("reader awoke, going to read"));
+      /* Stay locked. Leave the lock later by unlock_io_cache(). */
+      DBUG_RETURN(1);
+    }
 
-  pthread_mutex_unlock(&s->mutex);
-  return 0;
+    /* Another thread did read the block already. */
+  }
+  DBUG_PRINT("io_cache_share", ("reader awoke, going to process %u bytes",
+                                cshare->read_end ? (uint)
+                                (cshare->read_end - cshare->buffer) : 0));
+
+  /*
+    Leave the lock. Do not call unlock_io_cache() later. The thread that
+    filled the buffer did this and marked all threads as running.
+  */
+  pthread_mutex_unlock(&cshare->mutex);
+  DBUG_RETURN(0);
 }
 
-static void unlock_io_cache(IO_CACHE *info)
+
+/*
+  Unlock IO cache.
+
+  SYNOPSIS
+    unlock_io_cache()
+      cache                     The cache of the thread leaving the lock.
+
+  NOTE
+    This is called by the thread that filled the buffer. It marks all
+    threads as running and awakes them. This must not be done by any
+    other thread.
+
+    Do not signal cond_writer. Either there is no writer or the writer
+    is the only one who can call this function.
+
+    The reason for resetting running_threads to total_threads before
+    waking all other threads is that it could be possible that this
+    thread is so fast with processing the buffer that it enters the lock
+    before even one other thread has left it. If every awoken thread
+    would increase running_threads by one, this thread could think that
+    he is again the last to join and would not wait for the other
+    threads to process the data.
+
+  RETURN
+    void
+*/
+
+static void unlock_io_cache(IO_CACHE *cache)
 {
-  pthread_cond_broadcast(&info->share->cond);
-  pthread_mutex_unlock(&info->share->mutex);
+  IO_CACHE_SHARE *cshare= cache->share;
+  DBUG_ENTER("unlock_io_cache");
+  DBUG_PRINT("io_cache_share", ("%s: 0x%lx  pos: %lu  running: %u",
+                                (cache == cshare->source_cache) ?
+                                "writer" : "reader",
+                                cache, (ulong) cshare->pos_in_file,
+                                cshare->total_threads));
+
+  cshare->running_threads= cshare->total_threads;
+  pthread_cond_broadcast(&cshare->cond);
+  pthread_mutex_unlock(&cshare->mutex);
+  DBUG_VOID_RETURN;
 }
 
 
@@ -567,7 +867,7 @@ static void unlock_io_cache(IO_CACHE *info)
 
   SYNOPSIS
     _my_b_read_r()
-      info                      IO_CACHE pointer
+      cache                     IO_CACHE pointer
       Buffer                    Buffer to retrieve count bytes from file
       Count                     Number of bytes to read into Buffer
 
@@ -579,7 +879,7 @@ static void unlock_io_cache(IO_CACHE *info)
 
     It works as follows: when a thread tries to read from a file (that
     is, after using all the data from the (shared) buffer), it just
-    hangs on lock_io_cache(), wating for other threads. When the very
+    hangs on lock_io_cache(), waiting for other threads. When the very
     last thread attempts a read, lock_io_cache() returns 1, the thread
     does actual IO and unlock_io_cache(), which signals all the waiting
     threads that data is in the buffer.
@@ -599,16 +899,17 @@ static void unlock_io_cache(IO_CACHE *info)
     1      Error: can't read requested characters
 */
 
-int _my_b_read_r(register IO_CACHE *info, byte *Buffer, uint Count)
+int _my_b_read_r(register IO_CACHE *cache, byte *Buffer, uint Count)
 {
   my_off_t pos_in_file;
   uint length, diff_length, left_length;
+  IO_CACHE_SHARE *cshare= cache->share;
   DBUG_ENTER("_my_b_read_r");
 
-  if ((left_length= (uint) (info->read_end - info->read_pos)))
+  if ((left_length= (uint) (cache->read_end - cache->read_pos)))
   {
     DBUG_ASSERT(Count >= left_length);	/* User is not using my_b_read() */
-    memcpy(Buffer, info->read_pos, (size_t) (left_length));
+    memcpy(Buffer, cache->read_pos, (size_t) (left_length));
     Buffer+= left_length;
     Count-= left_length;
   }
@@ -616,55 +917,133 @@ int _my_b_read_r(register IO_CACHE *info, byte *Buffer, uint Count)
   {
     int cnt, len;
 
-    pos_in_file= info->pos_in_file + (info->read_end - info->buffer);
+    pos_in_file= cache->pos_in_file + (cache->read_end - cache->buffer);
     diff_length= (uint) (pos_in_file & (IO_SIZE-1));
     length=IO_ROUND_UP(Count+diff_length)-diff_length;
-    length=(length <= info->read_length) ?
-                   length + IO_ROUND_DN(info->read_length - length) :
-                   length - IO_ROUND_UP(length - info->read_length) ;
-    if (info->type != READ_FIFO &&
-	(length > (info->end_of_file - pos_in_file)))
-      length= (uint) (info->end_of_file - pos_in_file);
+    length= ((length <= cache->read_length) ?
+             length + IO_ROUND_DN(cache->read_length - length) :
+             length - IO_ROUND_UP(length - cache->read_length));
+    if (cache->type != READ_FIFO &&
+	(length > (cache->end_of_file - pos_in_file)))
+      length= (uint) (cache->end_of_file - pos_in_file);
     if (length == 0)
     {
-      info->error= (int) left_length;
+      cache->error= (int) left_length;
       DBUG_RETURN(1);
     }
-    if (lock_io_cache(info, pos_in_file))
+    if (lock_io_cache(cache, pos_in_file))
     {
-      info->share->active=info;
-      if (info->seek_not_done)             /* File touched, do seek */
-        VOID(my_seek(info->file,pos_in_file,MY_SEEK_SET,MYF(0)));
-      len=(int)my_read(info->file,info->buffer, length, info->myflags);
-      info->read_end=info->buffer + (len == -1 ? 0 : len);
-      info->error=(len == (int)length ? 0 : len);
-      info->pos_in_file=pos_in_file;
-      unlock_io_cache(info);
+      /* With a synchronized write/read cache we won't come here... */
+      DBUG_ASSERT(!cshare->source_cache);
+      /*
+        ... unless the writer has gone before this thread entered the
+        lock. Simulate EOF in this case. It can be distinguished by
+        cache->file.
+      */
+      if (cache->file < 0)
+        len= 0;
+      else
+      {
+        if (cache->seek_not_done)             /* File touched, do seek */
+          VOID(my_seek(cache->file, pos_in_file, MY_SEEK_SET, MYF(0)));
+        len= (int) my_read(cache->file, cache->buffer, length, cache->myflags);
+      }
+      DBUG_PRINT("io_cache_share", ("read %d bytes", len));
+
+      cache->read_end=    cache->buffer + (len == -1 ? 0 : len);
+      cache->error=       (len == (int)length ? 0 : len);
+      cache->pos_in_file= pos_in_file;
+
+      /* Copy important values to the share. */
+      cshare->error=       cache->error;
+      cshare->read_end=    cache->read_end;
+      cshare->pos_in_file= pos_in_file;
+
+      /* Mark all threads as running and wake them. */
+      unlock_io_cache(cache);
     }
     else
     {
-      info->error=          info->share->active->error;
-      info->read_end=       info->share->active->read_end;
-      info->pos_in_file=    info->share->active->pos_in_file;
-      len= (info->error == -1 ? -1 : info->read_end-info->buffer);
+      /*
+        With a synchronized write/read cache readers always come here.
+        Copy important values from the share.
+      */
+      cache->error=       cshare->error;
+      cache->read_end=    cshare->read_end;
+      cache->pos_in_file= cshare->pos_in_file;
+
+      len= ((cache->error == -1) ? -1 : cache->read_end - cache->buffer);
     }
-    info->read_pos=info->buffer;
-    info->seek_not_done=0;
+    cache->read_pos=      cache->buffer;
+    cache->seek_not_done= 0;
     if (len <= 0)
     {
-      info->error= (int) left_length;
+      DBUG_PRINT("io_cache_share", ("reader error. len %d  left %u",
+                                    len, left_length));
+      cache->error= (int) left_length;
       DBUG_RETURN(1);
     }
     cnt= ((uint) len > Count) ? (int) Count : len;
-    memcpy(Buffer, info->read_pos, (size_t) cnt);
+    memcpy(Buffer, cache->read_pos, (size_t) cnt);
     Count -= cnt;
     Buffer+= cnt;
     left_length+= cnt;
-    info->read_pos+= cnt;
+    cache->read_pos+= cnt;
   }
   DBUG_RETURN(0);
 }
-#endif
+
+
+/*
+  Copy data from write cache to read cache.
+
+  SYNOPSIS
+    copy_to_read_buffer()
+      write_cache               The write cache.
+      write_buffer              The source of data, mostly the cache buffer.
+      write_length              The number of bytes to copy.
+
+  NOTE
+    The write thread will wait for all read threads to join the cache
+    lock. Then it copies the data over and wakes the read threads.
+
+  RETURN
+    void
+*/
+
+static void copy_to_read_buffer(IO_CACHE *write_cache,
+                                const byte *write_buffer, uint write_length)
+{
+  IO_CACHE_SHARE *cshare= write_cache->share;
+
+  DBUG_ASSERT(cshare->source_cache == write_cache);
+  /*
+    write_length is usually less or equal to buffer_length.
+    It can be bigger if _my_b_write() is called with a big length.
+  */
+  while (write_length)
+  {
+    uint copy_length= min(write_length, write_cache->buffer_length);
+    int  __attribute__((unused)) rc;
+
+    rc= lock_io_cache(write_cache, write_cache->pos_in_file);
+    /* The writing thread does always have the lock when it awakes. */
+    DBUG_ASSERT(rc);
+
+    memcpy(cshare->buffer, write_buffer, copy_length);
+
+    cshare->error=       0;
+    cshare->read_end=    cshare->buffer + copy_length;
+    cshare->pos_in_file= write_cache->pos_in_file;
+
+    /* Mark all threads as running and wake them. */
+    unlock_io_cache(write_cache);
+
+    write_buffer+= copy_length;
+    write_length-= copy_length;
+  }
+}
+#endif /*THREAD*/
 
 
 /*
@@ -1016,6 +1395,7 @@ int _my_b_write(register IO_CACHE *info, const byte *Buffer, uint Count)
   Buffer+=rest_length;
   Count-=rest_length;
   info->write_pos+=rest_length;
+
   if (flush_io_cache(info))
     return 1;
   if (Count >= IO_SIZE)
@@ -1028,6 +1408,23 @@ int _my_b_write(register IO_CACHE *info, const byte *Buffer, uint Count)
     }
     if (my_write(info->file,Buffer,(uint) length,info->myflags | MY_NABP))
       return info->error= -1;
+
+#ifdef THREAD
+    /*
+      In case of a shared I/O cache with a writer we normally do direct
+      write cache to read cache copy. Simulate this here by direct
+      caller buffer to read cache copy. Do it after the write so that
+      the cache readers actions on the flushed part can go in parallel
+      with the write of the extra stuff. copy_to_read_buffer()
+      synchronizes writer and readers so that after this call the
+      readers can act on the extra stuff while the writer can go ahead
+      and prepare the next output. copy_to_read_buffer() relies on
+      info->pos_in_file.
+    */
+    if (info->share)
+      copy_to_read_buffer(info, Buffer, length);
+#endif
+
     Count-=length;
     Buffer+=length;
     info->pos_in_file+=length;
@@ -1048,6 +1445,14 @@ int my_b_append(register IO_CACHE *info, const byte *Buffer, uint Count)
 {
   uint rest_length,length;
 
+#ifdef THREAD
+  /*
+    Assert that we cannot come here with a shared cache. If we do one
+    day, we might need to add a call to copy_to_read_buffer().
+  */
+  DBUG_ASSERT(!info->share);
+#endif
+
   lock_append_buffer(info);
   rest_length=(uint) (info->write_end - info->write_pos);
   if (Count <= rest_length)
@@ -1108,6 +1513,14 @@ int my_block_write(register IO_CACHE *info, const byte *Buffer, uint Count,
   uint length;
   int error=0;
 
+#ifdef THREAD
+  /*
+    Assert that we cannot come here with a shared cache. If we do one
+    day, we might need to add a call to copy_to_read_buffer().
+  */
+  DBUG_ASSERT(!info->share);
+#endif
+
   if (pos < info->pos_in_file)
   {
     /* Of no overlap, write everything without buffering */
@@ -1184,6 +1597,17 @@ int my_b_flush_io_cache(IO_CACHE *info, int need_append_buffer_lock)
 
     if ((length=(uint) (info->write_pos - info->write_buffer)))
     {
+#ifdef THREAD
+      /*
+        In case of a shared I/O cache with a writer we do direct write
+        cache to read cache copy. Do it before the write here so that
+        the readers can work in parallel with the write.
+        copy_to_read_buffer() relies on info->pos_in_file.
+      */
+      if (info->share)
+        copy_to_read_buffer(info, info->write_buffer, length);
+#endif
+
       pos_in_file=info->pos_in_file;
       /*
 	If we have append cache, we always open the file with
@@ -1262,16 +1686,10 @@ int end_io_cache(IO_CACHE *info)
 
 #ifdef THREAD
   /*
-    if IO_CACHE is shared between several threads, only one
-    thread needs to call end_io_cache() - just as init_io_cache()
-    should be called only once and then memcopy'ed
+    Every thread must call remove_io_thread(). The last one destroys
+    the share elements.
   */
-  if (info->share)
-  {
-    pthread_cond_destroy (&info->share->cond);
-    pthread_mutex_destroy(&info->share->mutex);
-    info->share=0;
-  }
+  DBUG_ASSERT(!info->share || !info->share->total_threads);
 #endif
 
   if ((pre_close=info->pre_close))