MDEV-21263: Allow packed values of non-sorted fields in the sort buffer

This task deals with packing the non-sorted fields (or addon fields).
This would lead to efficient usage of the memory allocated for the sort buffer.
The changes brought by this feature are
  1) Sort buffers would have records of variable length
  2) Each record in the sort buffer would be stored like
     <sort_key1><sort_key2>....<addon_length><null_bytes><field1><field2>....
     addon_length is the extra bytes that are required to store the variable
     length of addon field across different records.
  3) Changes in rr_unpack_from_buffer and rr_from_tempfile to take into account
     the variable length of records.

Ported  WL#1509 Pack values of non-sorted fields in the sort buffer from
MySQL by Tor Didriksen

1 files changed, 113 insertions, 28 deletions

diff --git a/sql/records.cc b/sql/records.cc
index 3d709182a4e..2b146abb005 100644
--- a/sql/records.cc
+++ b/sql/records.cc
@@ -38,8 +38,8 @@
 static int rr_quick(READ_RECORD *info);
 int rr_sequential(READ_RECORD *info);
 static int rr_from_tempfile(READ_RECORD *info);
-static int rr_unpack_from_tempfile(READ_RECORD *info);
-static int rr_unpack_from_buffer(READ_RECORD *info);
+template<bool> static int rr_unpack_from_tempfile(READ_RECORD *info);
+template<bool> static int rr_unpack_from_buffer(READ_RECORD *info);
 int rr_from_pointers(READ_RECORD *info);
 static int rr_from_cache(READ_RECORD *info);
 static int init_rr_cache(THD *thd, READ_RECORD *info);
@@ -187,23 +187,23 @@ bool init_read_record(READ_RECORD *info,THD *thd, TABLE *table,
                       bool disable_rr_cache)
 {
   IO_CACHE *tempfile;
-  SORT_ADDON_FIELD *addon_field= filesort ? filesort->addon_field : 0;
   DBUG_ENTER("init_read_record");
 
+  const bool using_addon_fields= filesort && filesort->using_addon_fields();
+
   bzero((char*) info,sizeof(*info));
   info->thd=thd;
   info->table=table;
-  info->addon_field= addon_field;
+  info->sort_info= filesort;
   
   if ((table->s->tmp_table == INTERNAL_TMP_TABLE) &&
-      !addon_field)
+      !using_addon_fields)
     (void) table->file->extra(HA_EXTRA_MMAP);
   
-  if (addon_field)
+  if (using_addon_fields)
   {
-    info->rec_buf=    (uchar*) filesort->addon_buf.str;
-    info->ref_length= (uint)filesort->addon_buf.length;
-    info->unpack=     filesort->unpack;
+    info->rec_buf=    filesort->addon_fields->get_addon_buf();
+    info->ref_length= filesort->addon_fields->get_addon_buf_length();
   }
   else
   {
@@ -223,9 +223,20 @@ bool init_read_record(READ_RECORD *info,THD *thd, TABLE *table,
 
   if (tempfile && !(select && select->quick))
   {
-    DBUG_PRINT("info",("using rr_from_tempfile"));
-    info->read_record_func=
-        addon_field ? rr_unpack_from_tempfile : rr_from_tempfile;
+    if (using_addon_fields)
+    {
+      DBUG_PRINT("info",("using rr_from_tempfile"));
+      if (filesort->addon_fields->using_packed_addons())
+        info->read_record_func= rr_unpack_from_tempfile<true>;
+      else
+        info->read_record_func= rr_unpack_from_tempfile<false>;
+    }
+    else
+    {
+      DBUG_PRINT("info",("using rr_from_tempfile"));
+      info->read_record_func= rr_from_tempfile;
+    }
+
     info->io_cache= tempfile;
     reinit_io_cache(info->io_cache,READ_CACHE,0L,0,0);
     info->ref_pos=table->file->ref;
@@ -239,7 +250,7 @@ bool init_read_record(READ_RECORD *info,THD *thd, TABLE *table,
       and filesort->io_cache is read sequentially
     */
     if (!disable_rr_cache &&
-        !addon_field &&
+        !using_addon_fields &&
 	thd->variables.read_rnd_buff_size &&
 	!(table->file->ha_table_flags() & HA_FAST_KEY_READ) &&
 	(table->db_stat & HA_READ_ONLY ||
@@ -264,16 +275,29 @@ bool init_read_record(READ_RECORD *info,THD *thd, TABLE *table,
     DBUG_PRINT("info",("using rr_quick"));
     info->read_record_func= rr_quick;
   }
-  else if (filesort && filesort->record_pointers)
+  else if (filesort && filesort->has_filesort_result_in_memory())
   {
     DBUG_PRINT("info",("using record_pointers"));
     if (unlikely(table->file->ha_rnd_init_with_error(0)))
       DBUG_RETURN(1);
+
     info->cache_pos= filesort->record_pointers;
-    info->cache_end= (info->cache_pos+ 
-                      filesort->return_rows * info->ref_length);
-    info->read_record_func=
-        addon_field ? rr_unpack_from_buffer : rr_from_pointers;
+    if (using_addon_fields)
+    {
+      DBUG_PRINT("info",("using rr_unpack_from_buffer"));
+      DBUG_ASSERT(filesort->sorted_result_in_fsbuf);
+      info->unpack_counter= 0;
+      if (filesort->using_packed_addons())
+        info->read_record_func= rr_unpack_from_buffer<true>;
+      else
+        info->read_record_func= rr_unpack_from_buffer<false>;
+    }
+    else
+    {
+      info->cache_end= (info->cache_pos+
+                        filesort->return_rows * info->ref_length);
+      info->read_record_func= rr_from_pointers;
+    }
   }
   else if (table->file->keyread_enabled())
   {
@@ -510,7 +534,11 @@ static int rr_from_tempfile(READ_RECORD *info)
   the fields values use in the result set from this buffer into their
   positions in the regular record buffer.
 
-  @param info          Reference to the context including record descriptors
+  @param info                 Reference to the context including record
+                              descriptors
+  @param Packed_addon_fields  Are the addon fields packed?
+                              This is a compile-time constant, to
+                              avoid if (....) tests during execution.
 
   @retval
     0   Record successfully read.
@@ -518,12 +546,38 @@ static int rr_from_tempfile(READ_RECORD *info)
     -1   There is no record to be read anymore.
 */
 
+template<bool Packed_addon_fields>
 static int rr_unpack_from_tempfile(READ_RECORD *info)
 {
-  if (my_b_read(info->io_cache, info->rec_buf, info->ref_length))
-    return -1;
-  (*info->unpack)(info->addon_field, info->rec_buf,
-                  info->rec_buf + info->ref_length);
+  uchar *destination= info->rec_buf;
+#ifndef DBUG_OFF
+  my_off_t where= my_b_tell(info->io_cache);
+#endif
+  if (Packed_addon_fields)
+  {
+    const uint len_sz= Addon_fields::size_of_length_field;
+
+    // First read length of the record.
+    if (my_b_read(info->io_cache, destination, len_sz))
+      return -1;
+    uint res_length= Addon_fields::read_addon_length(destination);
+    DBUG_PRINT("info", ("rr_unpack from %llu to %p sz %u",
+                        static_cast<ulonglong>(where),
+                        destination, res_length));
+    DBUG_ASSERT(res_length > len_sz);
+    DBUG_ASSERT(info->sort_info->using_addon_fields());
+
+    // Then read the rest of the record.
+    if (my_b_read(info->io_cache, destination + len_sz, res_length - len_sz))
+      return -1;                                /* purecov: inspected */
+  }
+  else
+  {
+    if (my_b_read(info->io_cache, destination, info->ref_length))
+      return -1;
+  }
+
+  info->sort_info->unpack_addon_fields<Packed_addon_fields>(destination);
 
   return 0;
 }
@@ -560,7 +614,11 @@ int rr_from_pointers(READ_RECORD *info)
   the fields values use in the result set from this buffer into their
   positions in the regular record buffer.
 
-  @param info          Reference to the context including record descriptors
+  @param info                 Reference to the context including record
+                              descriptors
+  @param Packed_addon_fields  Are the addon fields packed?
+                              This is a compile-time constant, to
+                              avoid if (....) tests during execution.
 
   @retval
     0   Record successfully read.
@@ -568,13 +626,17 @@ int rr_from_pointers(READ_RECORD *info)
     -1   There is no record to be read anymore.
 */
 
+template<bool Packed_addon_fields>
 static int rr_unpack_from_buffer(READ_RECORD *info)
 {
-  if (info->cache_pos == info->cache_end)
+  if (info->unpack_counter == info->sort_info->return_rows)
     return -1;                      /* End of buffer */
-  (*info->unpack)(info->addon_field, info->cache_pos,
-                  info->cache_end);
-  info->cache_pos+= info->ref_length;
+
+  uchar *record= info->sort_info->get_sorted_record(
+    static_cast<uint>(info->unpack_counter));
+  uchar *plen= record + info->sort_info->get_sort_length();
+  info->sort_info->unpack_addon_fields<Packed_addon_fields>(plen);
+  info->unpack_counter++;
   return 0;
 }
 	/* cacheing of records from a database */
@@ -709,3 +771,26 @@ static int rr_cmp(uchar *a,uchar *b)
   return (int) a[7] - (int) b[7];
 #endif
 }
+
+template<bool Packed_addon_fields>
+inline void SORT_INFO::unpack_addon_fields(uchar *buff)
+{
+  SORT_ADDON_FIELD *addonf= addon_fields->begin();
+  uchar *buff_end= buff + sort_buffer_size();
+  const uchar *start_of_record= buff + addonf->offset;
+
+  for ( ; addonf != addon_fields->end() ; addonf++)
+  {
+    Field *field= addonf->field;
+    if (addonf->null_bit && (addonf->null_bit & buff[addonf->null_offset]))
+    {
+      field->set_null();
+      continue;
+    }
+    field->set_notnull();
+    if (Packed_addon_fields)
+      start_of_record= field->unpack(field->ptr, start_of_record, buff_end, 0);
+    else
+      field->unpack(field->ptr, buff + addonf->offset, buff_end, 0);
+  }
+}