Bug#8283 - OPTIMIZE TABLE causes data loss

OPTIMIZE TABLE with myisam_repair_threads > 1 performs a non-quick 
parallel repair. This means that it does not only rebuild all 
indexes, but also the data file.

Non-quick parallel repair works so that there is one thread per 
index. The first of the threads rebuilds also the new data file.

The problem was that all threads shared the read io cache on the
old data file. If there were holes (deleted records) in the table,
the first thread skipped them, writing only contiguous, non-deleted
records to the new data file. Then it built the new index so that
its entries pointed to the correct record positions. But the other
threads didn't know the new record positions, but put the positions
from the old data file into the index.

The new design is so that there is a shared io cache which is filled
by the first thread (the data file writer) with the new contiguous
records and read by the other threads. Now they know the new record
positions.

Another problem was that for the parallel repair of compressed
tables a common bit_buff and rec_buff was used. I changed it so
that thread specific buffers are used for parallel repair.

A similar problem existed for checksum calculation. I made this
multi-thread safe too.


include/my_sys.h:
  Bug#8283 - OPTIMIZE TABLE causes data loss
  Redesign of io_cache_share.
include/myisam.h:
  Bug#8283 - OPTIMIZE TABLE causes data loss
  Redesign of checksum calculation in mi_check.c.
  'calc_checksum' is now in myisamdef.h:st_mi_sort_param.
myisam/mi_check.c:
  Bug#8283 - OPTIMIZE TABLE causes data loss
  Implemented a new parallel repair design.
  Using a synchronized shared read/write cache.
  Allowed for thread specific bit_buff, rec_buff, and calc_checksum.
myisam/mi_open.c:
  Bug#8283 - OPTIMIZE TABLE causes data loss
  Added DBUG output.
myisam/mi_packrec.c:
  Bug#8283 - OPTIMIZE TABLE causes data loss
  Allowed for thread specific bit_buff and rec_buff.
myisam/myisamdef.h:
  Bug#8283 - OPTIMIZE TABLE causes data loss
  Commented on checksum calculation variables.
  Allowed for thread specific bit_buff.
  Added DBUG output for better table crash detection.
myisam/sort.c:
  Bug#8283 - OPTIMIZE TABLE causes data loss
  Added implications of the new parallel repair design.
  Renamed 'info' -> 'sort_param'.
  Added DBUG output.
mysql-test/r/myisam.result:
  Bug#8283 - OPTIMIZE TABLE causes data loss
  Added test results.
mysql-test/t/myisam.test:
  Bug#8283 - OPTIMIZE TABLE causes data loss
  Added test cases.
mysys/mf_iocache.c:
  Bug#8283 - OPTIMIZE TABLE causes data loss
  Redesign of io_cache_share.
  We do now allow a writer to synchronize himself with the
  readers of a shared cache. When all threads join in the lock,
  the writer copies the data from his write buffer to the shared
  read buffer.

5 files changed, 400 insertions, 143 deletions

diff --git a/myisam/mi_check.c b/myisam/mi_check.c
index 2395640d5bf..35b56419367 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));
@@ -1394,7 +1420,7 @@ 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++)
@@ -1418,7 +1444,7 @@ 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;
@@ -1563,11 +1589,13 @@ 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;
@@ -1621,8 +1649,8 @@ 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 */
@@ -2127,7 +2155,7 @@ 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 ;
@@ -2189,7 +2217,8 @@ 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;
@@ -2352,6 +2381,28 @@ 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
@@ -2374,6 +2425,7 @@ 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;
@@ -2395,19 +2447,55 @@ 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;
@@ -2497,8 +2585,6 @@ 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 *
@@ -2548,6 +2634,7 @@ 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;
@@ -2584,19 +2671,45 @@ 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...
@@ -2614,7 +2727,10 @@ 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
@@ -2636,6 +2752,11 @@ 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)
@@ -2651,8 +2772,14 @@ 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;
   }
@@ -2707,7 +2834,20 @@ 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 */
@@ -2838,12 +2978,41 @@ 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;
@@ -2881,7 +3050,7 @@ 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);
@@ -2896,6 +3065,7 @@ 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;
@@ -2926,7 +3096,7 @@ 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)
 	  {
@@ -3103,9 +3273,31 @@ 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",
@@ -3135,13 +3327,14 @@ 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",
@@ -3149,7 +3342,7 @@ 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);
       }
@@ -3176,7 +3369,8 @@ 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 ==
@@ -3200,15 +3394,14 @@ 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;
@@ -3218,8 +3411,9 @@ 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);
     }
   }
@@ -3227,7 +3421,20 @@ 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)
 {
@@ -3276,6 +3483,7 @@ 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;
@@ -3685,7 +3893,7 @@ 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 bd2d162d100..c425bf54b1a 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
 
@@ -428,13 +429,15 @@ 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:
@@ -443,8 +446,8 @@ 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;
@@ -452,18 +455,18 @@ 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);
@@ -977,13 +980,16 @@ 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
@@ -996,9 +1002,9 @@ 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
@@ -1013,8 +1019,8 @@ 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);
 }
@@ -1022,8 +1028,9 @@ 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;
@@ -1048,17 +1055,17 @@ 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;
 }
@@ -1198,7 +1205,8 @@ 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,
@@ -1209,10 +1217,10 @@ 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;
 }
@@ -1228,11 +1236,13 @@ 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));
 }
 
 
@@ -1252,7 +1262,8 @@ 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))))
@@ -1269,7 +1280,8 @@ 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 96b55d599c8..2e6fd20ade8 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 ;
@@ -604,7 +626,7 @@ 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 */