MDEV-21580: Allow packed sort keys in sort bufferbb-10.5-mdev6915-ext

This task deals with packing the sort key inside the sort buffer, which  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 sort keys of variable length
  2) The format for sort keys inside the sort buffer would look like
     |<sort_length><null_byte><key_part1><null_byte><key_part2>.......|
      sort_length is the extra bytes that are required to store the variable
      length of a sort key.
  3) When packing of sort key is done we store the ORIGINAL VALUES inside
     the sort buffer and not the STRXFRM form (mem-comparable sort keys).
  4) Special comparison function packed_keys_comparison() is introduced
     to compare 2 sort keys.

1 files changed, 33 insertions, 5 deletions

diff --git a/sql/records.cc b/sql/records.cc
index 2b146abb005..e1766322e2f 100644
--- a/sql/records.cc
+++ b/sql/records.cc
@@ -39,7 +39,7 @@ static int rr_quick(READ_RECORD *info);
 int rr_sequential(READ_RECORD *info);
 static int rr_from_tempfile(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);
+template<bool,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);
@@ -190,6 +190,7 @@ bool init_read_record(READ_RECORD *info,THD *thd, TABLE *table,
   DBUG_ENTER("init_read_record");
 
   const bool using_addon_fields= filesort && filesort->using_addon_fields();
+  bool using_packed_sortkeys= filesort && filesort->using_packed_sortkeys();
 
   bzero((char*) info,sizeof(*info));
   info->thd=thd;
@@ -287,10 +288,19 @@ bool init_read_record(READ_RECORD *info,THD *thd, TABLE *table,
       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>;
+      {
+        info->read_record_func= using_packed_sortkeys ?
+                                rr_unpack_from_buffer<true, true> :
+                                rr_unpack_from_buffer<true, false>;
+      }
       else
-        info->read_record_func= rr_unpack_from_buffer<false>;
+      {
+        info->read_record_func= using_packed_sortkeys ?
+                                rr_unpack_from_buffer<false, true> :
+                                rr_unpack_from_buffer<false, false>;
+      }
     }
     else
     {
@@ -626,7 +636,7 @@ int rr_from_pointers(READ_RECORD *info)
     -1   There is no record to be read anymore.
 */
 
-template<bool Packed_addon_fields>
+template<bool Packed_addon_fields, bool Packed_sort_keys>
 static int rr_unpack_from_buffer(READ_RECORD *info)
 {
   if (info->unpack_counter == info->sort_info->return_rows)
@@ -634,7 +644,12 @@ static int rr_unpack_from_buffer(READ_RECORD *info)
 
   uchar *record= info->sort_info->get_sorted_record(
     static_cast<uint>(info->unpack_counter));
-  uchar *plen= record + info->sort_info->get_sort_length();
+
+  uint sort_length= Packed_sort_keys ?
+                    Sort_keys::read_sortkey_length(record):
+                    info->sort_info->get_sort_length();
+
+  uchar *plen= record + sort_length;
   info->sort_info->unpack_addon_fields<Packed_addon_fields>(plen);
   info->unpack_counter++;
   return 0;
@@ -772,6 +787,19 @@ static int rr_cmp(uchar *a,uchar *b)
 #endif
 }
 
+
+/**
+  Copy (unpack) values appended to sorted fields from a buffer back to
+  their regular positions specified by the Field::ptr pointers.
+
+  @param addon_field     Array of descriptors for appended fields
+  @param buff            Buffer which to unpack the value from
+
+  @note
+    The function is supposed to be used only as a callback function
+    when getting field values for the sorted result set.
+
+*/
 template<bool Packed_addon_fields>
 inline void SORT_INFO::unpack_addon_fields(uchar *buff)
 {