WL#1687 - Optimize UNION DISTINCT ... UNION ALL (again).

HEAP: Copies the key count to a backup variable and sets the key count to zero.
That way, no HEAP function will ever try to touch any index.
Re-enabling is done by copying back the backup variable.
To avoid memory leak at table close, disable deletes all index trees.
Re-enabling must be done with empty indexes and data anyway. Otherwise,
the indexes would need to be repaired, wich HEAP is not capable of.
MyISAM: Only the key_map is cleared and set.
Re-enabling must be done with empty indexes and data. Otherwise, repair needs
to be done which will enable all keys persistently.
The former implementation disabled only non-unique keys and maked this persistent.
The new implementation additionally can disable all keys, but only without
making this persistent. Re-enabling all keys can be done without repair,
if data file and indexes are empty.

2 files changed, 141 insertions, 7 deletions

diff --git a/heap/heapdef.h b/heap/heapdef.h
index 63109badb05..083765334ab 100644
--- a/heap/heapdef.h
+++ b/heap/heapdef.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
+/* Copyright (C) 2000,2004 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -97,6 +97,7 @@ extern uint hp_rb_null_key_length(HP_KEYDEF *keydef, const byte *key);
 extern my_bool hp_if_null_in_key(HP_KEYDEF *keyinfo, const byte *record);
 extern int hp_close(register HP_INFO *info);
 extern void hp_clear(HP_SHARE *info);
+extern void hp_clear_keys(HP_SHARE *info);
 extern uint hp_rb_pack_key(HP_KEYDEF *keydef, uchar *key, const uchar *old, 
 			   uint k_len);
 #ifdef THREAD
diff --git a/heap/hp_clear.c b/heap/hp_clear.c
index e65d3a172c3..4440344f990 100644
--- a/heap/hp_clear.c
+++ b/heap/hp_clear.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
+/* Copyright (C) 2000,2004 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -29,13 +29,60 @@ void heap_clear(HP_INFO *info)
 
 void hp_clear(HP_SHARE *info)
 {
-  uint key;
   DBUG_ENTER("hp_clear");
 
   if (info->block.levels)
     VOID(hp_free_level(&info->block,info->block.levels,info->block.root,
 			(byte*) 0));
   info->block.levels=0;
+  hp_clear_keys(info);
+  info->records=info->deleted=info->data_length=0;
+  info->blength=1;
+  info->changed=0;
+  info->del_link=0;
+  DBUG_VOID_RETURN;
+}
+
+
+/*
+  Clear all keys.
+
+  SYNOPSIS
+    heap_clear_keys()
+    info      A pointer to the heap storage engine HP_INFO struct.
+
+  DESCRIPTION
+    Delete all trees of all indexes and leave them empty.
+
+  RETURN
+    void
+*/
+
+void heap_clear_keys(HP_INFO *info)
+{
+  hp_clear(info->s);
+}
+
+
+/*
+  Clear all keys.
+
+  SYNOPSIS
+    hp_clear_keys()
+    info      A pointer to the heap storage engine HP_SHARE struct.
+
+  DESCRIPTION
+    Delete all trees of all indexes and leave them empty.
+
+  RETURN
+    void
+*/
+
+void hp_clear_keys(HP_SHARE *info)
+{
+  uint key;
+  DBUG_ENTER("hp_clear_keys");
+
   for (key=0 ; key < info->keys ; key++)
   {
     HP_KEYDEF *keyinfo = info->keydef + key;
@@ -52,9 +99,95 @@ void hp_clear(HP_SHARE *info)
       block->last_allocated=0;
     }
   }
-  info->records=info->deleted=info->data_length=info->index_length=0;
-  info->blength=1;
-  info->changed=0;
-  info->del_link=0;
+  info->index_length=0;
   DBUG_VOID_RETURN;
 }
+
+
+/*
+  Disable all indexes.
+
+  SYNOPSIS
+    heap_disable_indexes()
+    info      A pointer to the heap storage engine HP_INFO struct.
+
+  DESCRIPTION
+    Disable and clear (remove contents of) all indexes.
+
+  RETURN
+    0  ok
+*/
+
+int heap_disable_indexes(HP_INFO *info)
+{
+  HP_SHARE *share= info->s;
+
+  if (share->keys)
+  {
+    hp_clear_keys(share);
+    share->currently_disabled_keys= share->keys;
+    share->keys= 0;
+  }
+  return 0;
+}
+
+
+/*
+  Enable all indexes
+
+  SYNOPSIS
+    heap_enable_indexes()
+    info      A pointer to the heap storage engine HP_INFO struct.
+
+  DESCRIPTION
+    Enable all indexes. The indexes might have been disabled
+    by heap_disable_index() before.
+    The function works only if both data and indexes are empty,
+    since the heap storage engine cannot repair the indexes.
+    To be sure, call handler::delete_all_rows() before.
+
+  RETURN
+    0  ok
+    HA_ERR_CRASHED data or index is non-empty.
+*/
+
+int heap_enable_indexes(HP_INFO *info)
+{
+  int error= 0;
+  HP_SHARE *share= info->s;
+
+  if (share->data_length || share->index_length)
+    error= HA_ERR_CRASHED;
+  else
+    if (share->currently_disabled_keys)
+    {
+      share->keys= share->currently_disabled_keys;
+      share->currently_disabled_keys= 0;
+    }
+  return error;
+}
+
+
+/*
+  Test if indexes are disabled.
+
+  SYNOPSIS
+    heap_indexes_are_disabled()
+    info      A pointer to the heap storage engine HP_INFO struct.
+
+  DESCRIPTION
+    Test if indexes are disabled.
+
+  RETURN
+    0  indexes are not disabled
+    1  all indexes are disabled
+   [2  non-unique indexes are disabled - NOT YET IMPLEMENTED]
+*/
+
+int heap_indexes_are_disabled(HP_INFO *info)
+{
+  HP_SHARE *share= info->s;
+
+  return (! share->keys && share->currently_disabled_keys);
+}
+