Bug#41660: Sort-index_merge for non-first join table may

require O(#scans) memory

When an index merge operation was restarted, it would
re-allocate the Unique object controlling the duplicate row
ID elimination. Fixed by making the Unique object a member
of QUICK_INDEX_MERGE_SELECT and thus reusing it throughout
the lifetime of this object.

1 files changed, 19 insertions, 18 deletions

diff --git a/sql/opt_range.cc b/sql/opt_range.cc
index 2f4281d539f..f2f14a2dcc9 100644
--- a/sql/opt_range.cc
+++ b/sql/opt_range.cc
@@ -1194,7 +1194,7 @@ QUICK_RANGE_SELECT::~QUICK_RANGE_SELECT()
 
 QUICK_INDEX_MERGE_SELECT::QUICK_INDEX_MERGE_SELECT(THD *thd_param,
                                                    TABLE *table)
-  :pk_quick_select(NULL), thd(thd_param)
+  :unique(NULL), pk_quick_select(NULL), thd(thd_param)
 {
   DBUG_ENTER("QUICK_INDEX_MERGE_SELECT::QUICK_INDEX_MERGE_SELECT");
   index= MAX_KEY;
@@ -1236,6 +1236,7 @@ QUICK_INDEX_MERGE_SELECT::~QUICK_INDEX_MERGE_SELECT()
   List_iterator_fast<QUICK_RANGE_SELECT> quick_it(quick_selects);
   QUICK_RANGE_SELECT* quick;
   DBUG_ENTER("QUICK_INDEX_MERGE_SELECT::~QUICK_INDEX_MERGE_SELECT");
+  delete unique;
   quick_it.rewind();
   while ((quick= quick_it++))
     quick->file= NULL;
@@ -8153,7 +8154,6 @@ int QUICK_INDEX_MERGE_SELECT::read_keys_and_merge()
   List_iterator_fast<QUICK_RANGE_SELECT> cur_quick_it(quick_selects);
   QUICK_RANGE_SELECT* cur_quick;
   int result;
-  Unique *unique;
   handler *file= head->file;
   DBUG_ENTER("QUICK_INDEX_MERGE_SELECT::read_keys_and_merge");
 
@@ -8172,9 +8172,22 @@ int QUICK_INDEX_MERGE_SELECT::read_keys_and_merge()
   if (cur_quick->init() || cur_quick->reset())
     DBUG_RETURN(1);
 
-  unique= new Unique(refpos_order_cmp, (void *)file,
-                     file->ref_length,
-                     thd->variables.sortbuff_size);
+  if (unique == NULL)
+  {
+    DBUG_EXECUTE_IF("index_merge_may_not_create_a_Unique", abort(); );
+    DBUG_EXECUTE_IF("only_one_Unique_may_be_created", 
+                    DBUG_SET("+d,index_merge_may_not_create_a_Unique"); );
+
+    unique= new Unique(refpos_order_cmp, (void *)file,
+                       file->ref_length,
+                       thd->variables.sortbuff_size);
+  }
+  else
+    unique->reset();
+
+  DBUG_ASSERT(file->ref_length == unique->get_size());
+  DBUG_ASSERT(thd->variables.sortbuff_size == unique->get_max_in_memory_size());
+
   if (!unique)
     DBUG_RETURN(1);
   for (;;)
@@ -8189,10 +8202,7 @@ int QUICK_INDEX_MERGE_SELECT::read_keys_and_merge()
       if (cur_quick->file->inited != handler::NONE) 
         cur_quick->file->ha_index_end();
       if (cur_quick->init() || cur_quick->reset())
-      {
-        delete unique;
         DBUG_RETURN(1);
-      }
     }
 
     if (result)
@@ -8200,17 +8210,13 @@ int QUICK_INDEX_MERGE_SELECT::read_keys_and_merge()
       if (result != HA_ERR_END_OF_FILE)
       {
         cur_quick->range_end();
-        delete unique;
         DBUG_RETURN(result);
       }
       break;
     }
 
     if (thd->killed)
-    {
-      delete unique;
       DBUG_RETURN(1);
-    }
 
     /* skip row if it will be retrieved by clustered PK scan */
     if (pk_quick_select && pk_quick_select->row_in_ranges())
@@ -8219,10 +8225,7 @@ int QUICK_INDEX_MERGE_SELECT::read_keys_and_merge()
     cur_quick->file->position(cur_quick->record);
     result= unique->unique_add((char*)cur_quick->file->ref);
     if (result)
-    {
-      delete unique;
       DBUG_RETURN(1);
-    }
   }
 
   /*
@@ -8231,7 +8234,6 @@ int QUICK_INDEX_MERGE_SELECT::read_keys_and_merge()
     sequence.
   */
   result= unique->get(head);
-  delete unique;
   doing_pk_scan= FALSE;
   /* index_merge currently doesn't support "using index" at all */
   head->set_keyread(FALSE);
@@ -10277,7 +10279,7 @@ QUICK_GROUP_MIN_MAX_SELECT(TABLE *table, JOIN *join_arg, bool have_min_arg,
                            uint use_index, double read_cost_arg,
                            ha_rows records_arg, uint key_infix_len_arg,
                            uchar *key_infix_arg, MEM_ROOT *parent_alloc)
-  :join(join_arg), index_info(index_info_arg),
+  :file(table->file), join(join_arg), index_info(index_info_arg),
    group_prefix_len(group_prefix_len_arg),
    group_key_parts(group_key_parts_arg), have_min(have_min_arg),
    have_max(have_max_arg), seen_first_key(FALSE),
@@ -10286,7 +10288,6 @@ QUICK_GROUP_MIN_MAX_SELECT(TABLE *table, JOIN *join_arg, bool have_min_arg,
    max_functions_it(NULL)
 {
   head=       table;
-  file=       head->file;
   index=      use_index;
   record=     head->record[0];
   tmp_record= head->record[1];