Merge spetrunia@bk-internal.mysql.com:/home/bk/mysql-4.1

into mysql.com:/dbdata/psergey/mysql-4.1-heap-bug

heap/_check.c

@@ -102,9 +102,11 @@ static int check_one_key(HP_KEYDEF *keydef, uint keynr, ulong records,
   int error;
   uint i,found,max_links,seek,links;
   uint rec_link;				/* Only used with debugging */
+  uint hash_buckets_found;
   HASH_INFO *hash_info;
 
   error=0;
+  hash_buckets_found= 0;
   for (i=found=max_links=seek=0 ; i < records ; i++)
   {
     hash_info=hp_find_hash(&keydef->block,i);
@@ -128,21 +130,32 @@ static int check_one_key(HP_KEYDEF *keydef, uint keynr, ulong records,
 	  found++;
       }
       if (links > max_links) max_links=links;
+      hash_buckets_found++;
     }
   }
   if (found != records)
   {
-    DBUG_PRINT("error",("Found %ld of %ld records"));
+    DBUG_PRINT("error",("Found %ld of %ld records", found, records));
+    error=1;
+  }
+  if (keydef->hash_buckets != hash_buckets_found)
+  {
+    DBUG_PRINT("error",("Found %ld buckets, stats shows %ld buckets",
+                        hash_buckets_found, keydef->hash_buckets));
     error=1;
   }
   DBUG_PRINT("info",
-	     ("records: %ld   seeks: %d   max links: %d   hitrate: %.2f",
+	     ("records: %ld   seeks: %d   max links: %d   hitrate: %.2f   "
+              "buckets: %d",
 	      records,seek,max_links,
-	      (float) seek / (float) (records ? records : 1)));
+	      (float) seek / (float) (records ? records : 1), 
+              hash_buckets_found));
   if (print_status)
-    printf("Key: %d  records: %ld   seeks: %d   max links: %d   hitrate: %.2f\n",
+    printf("Key: %d  records: %ld   seeks: %d   max links: %d   "
+           "hitrate: %.2f   buckets: %d\n",
 	   keynr, records, seek, max_links,
-	   (float) seek / (float) (records ? records : 1));
+	   (float) seek / (float) (records ? records : 1), 
+           hash_buckets_found);
   return error;
 }
 

heap/hp_block.c

@@ -18,12 +18,19 @@
 
 #include "heapdef.h"
 
-	/* Find record according to record-position */
+/*
+  Find record according to record-position.
+      
+  The record is located by factoring position number pos into (p_0, p_1, ...) 
+  such that
+     pos = SUM_i(block->level_info[i].records_under_level * p_i)
+  {p_0, p_1, ...} serve as indexes to descend the blocks tree.
+*/
 
 byte *hp_find_block(HP_BLOCK *block, ulong pos)
 {
   reg1 int i;
-  reg3 HP_PTRS *ptr;
+  reg3 HP_PTRS *ptr; /* block base ptr */
 
   for (i=block->levels-1, ptr=block->root ; i > 0 ; i--)
   {
@@ -34,8 +41,18 @@ byte *hp_find_block(HP_BLOCK *block, ulong pos)
 }
 
 
-	/* get one new block-of-records. Alloc ptr to block if neaded */
-	/* Interrupts are stopped to allow ha_panic in interrupts */
+/*
+  Get one new block-of-records. Alloc ptr to block if needed
+  SYNOPSIS
+    hp_get_new_block()
+      block             HP_BLOCK tree-like block
+      alloc_length OUT  Amount of memory allocated from the heap
+      
+  Interrupts are stopped to allow ha_panic in interrupts 
+  RETURN
+    0  OK
+    1  Out of memory
+*/
 
 int hp_get_new_block(HP_BLOCK *block, ulong *alloc_length)
 {
@@ -46,6 +63,18 @@ int hp_get_new_block(HP_BLOCK *block, ulong *alloc_length)
     if (block->level_info[i].free_ptrs_in_block)
       break;
 
+  /*
+    Allocate space for leaf block plus space for upper level blocks up to
+    first level that has a free slot to put the pointer. 
+    In some cases we actually allocate more then we need:
+    Consider e.g. a situation where we have one level 1 block and one level 0
+    block, the level 0 block is full and this function is called. We only 
+    need a leaf block in this case. Nevertheless, we will get here with i=1 
+    and will also allocate sizeof(HP_PTRS) for non-leaf block and will never 
+    use this space.
+    This doesn't add much overhead - with current values of sizeof(HP_PTRS) 
+    and my_default_record_cache_size we get about 1/128 unused memory.
+   */
   *alloc_length=sizeof(HP_PTRS)*i+block->records_in_block* block->recbuffer;
   if (!(root=(HP_PTRS*) my_malloc(*alloc_length,MYF(0))))
     return 1;
@@ -60,21 +89,33 @@ int hp_get_new_block(HP_BLOCK *block, ulong *alloc_length)
     dont_break();		/* Dont allow SIGHUP or SIGINT */
     if ((uint) i == block->levels)
     {
+      /* Adding a new level on top of the existing ones. */
       block->levels=i+1;
+      /*
+        Use first allocated HP_PTRS as a top-level block. Put the current
+        block tree into the first slot of a new top-level block.
+      */
       block->level_info[i].free_ptrs_in_block=HP_PTRS_IN_NOD-1;
       ((HP_PTRS**) root)[0]= block->root;
       block->root=block->level_info[i].last_blocks= root++;
     }
+    /* Occupy the free slot we've found at level i */
     block->level_info[i].last_blocks->
       blocks[HP_PTRS_IN_NOD - block->level_info[i].free_ptrs_in_block--]=
 	(byte*) root;
     
+    /* Add a block subtree with each node having one left-most child */
     for (j=i-1 ; j >0 ; j--)
     {
       block->level_info[j].last_blocks= root++;
       block->level_info[j].last_blocks->blocks[0]=(byte*) root;
       block->level_info[j].free_ptrs_in_block=HP_PTRS_IN_NOD-1;
     }
+    
+    /* 
+      root now points to last (block->records_in_block* block->recbuffer)
+      allocated bytes. Use it as a leaf block.
+    */
     block->level_info[0].last_blocks= root;
     allow_break();		/* Allow SIGHUP & SIGINT */
   }

heap/hp_clear.c

@@ -97,6 +97,7 @@ void hp_clear_keys(HP_SHARE *info)
         VOID(hp_free_level(block,block->levels,block->root,(byte*) 0));
       block->levels=0;
       block->last_allocated=0;
+      keyinfo->hash_buckets= 0;
     }
   }
   info->index_length=0;

heap/hp_create.c

@@ -128,6 +128,7 @@ int heap_create(const char *name, uint keys, HP_KEYDEF *keydef,
 		   max_records);
 	keyinfo->delete_key= hp_delete_key;
 	keyinfo->write_key= hp_write_key;
+        keyinfo->hash_buckets= 0;
       }
     }
     share->min_records= min_records;

heap/hp_delete.c

@@ -97,8 +97,8 @@ int hp_rb_delete_key(HP_INFO *info, register HP_KEYDEF *keyinfo,
     flag		Is set if we want's to correct info->current_ptr
 
   RETURN
-    0	ok
-    #	error number
+    0      Ok
+    other  Error code
 */
 
 int hp_delete_key(HP_INFO *info, register HP_KEYDEF *keyinfo,
@@ -151,6 +151,8 @@ int hp_delete_key(HP_INFO *info, register HP_KEYDEF *keyinfo,
     pos->ptr_to_rec=empty->ptr_to_rec;
     pos->next_key=empty->next_key;
   }
+  else
+    keyinfo->hash_buckets--;
 
   if (empty == lastpos)			/* deleted last hash key */
     DBUG_RETURN (0);
@@ -187,7 +189,11 @@ int hp_delete_key(HP_INFO *info, register HP_KEYDEF *keyinfo,
     }
     pos3= pos;				/* Link pos->next after lastpos */
   }
-  else pos3= 0;				/* Different positions merge */
+  else
+  {
+    pos3= 0;				/* Different positions merge */
+    keyinfo->hash_buckets--;
+  }
 
   empty[0]=lastpos[0];
   hp_movelink(pos3, empty, pos->next_key);

heap/hp_hash.c

@@ -196,7 +196,18 @@ byte *hp_search_next(HP_INFO *info, HP_KEYDEF *keyinfo, const byte *key,
 }
 
 
-	/* Calculate pos according to keys */
+/*
+  Calculate position number for hash value.
+  SYNOPSIS
+    hp_mask()
+      hashnr     Hash value
+      buffmax    Value such that
+                 2^(n-1) < maxlength <= 2^n = buffmax
+      maxlength  
+  
+  RETURN
+    Array index, in [0..maxlength)
+*/
 
 ulong hp_mask(ulong hashnr, ulong buffmax, ulong maxlength)
 {
@@ -205,7 +216,12 @@ ulong hp_mask(ulong hashnr, ulong buffmax, ulong maxlength)
 }
 
 
-	/* Change link from pos to new_link */
+/*
+  Change
+    next_link -> ... -> X -> pos
+  to
+    next_link -> ... -> X -> newlink
+*/
 
 void hp_movelink(HASH_INFO *pos, HASH_INFO *next_link, HASH_INFO *newlink)
 {

heap/hp_write.c

@@ -36,7 +36,6 @@ int heap_write(HP_INFO *info, const byte *record)
   byte *pos;
   HP_SHARE *share=info->s;
   DBUG_ENTER("heap_write");
-
 #ifndef DBUG_OFF
   if (info->mode & O_RDONLY)
   {
@@ -160,7 +159,31 @@ static byte *next_free_record_pos(HP_SHARE *info)
 	      block_pos*info->block.recbuffer);
 }
 
-	/* Write a hash-key to the hash-index */
+
+/*
+  Write a hash-key to the hash-index
+  SYNOPSIS
+    info     Heap table info
+    keyinfo  Key info
+    record   Table record to added
+    recpos   Memory buffer where the table record will be stored if added 
+             successfully
+  NOTE
+    Hash index uses HP_BLOCK structure as a 'growable array' of HASH_INFO 
+    structs. Array size == number of entries in hash index.
+    hp_mask(hp_rec_hashnr()) maps hash entries values to hash array positions.
+    If there are several hash entries with the same hash array position P,
+    they are connected in a linked list via HASH_INFO::next_key. The first 
+    list element is located at position P, next elements are located at 
+    positions for which there is no record that should be located at that
+    position. The order of elements in the list is arbitrary.
+
+  RETURN
+    0  - OK
+    -1 - Out of memory
+    HA_ERR_FOUND_DUPP_KEY - Duplicate record on unique key. The record was 
+    still added and the caller must call hp_delete_key for it.
+*/
 
 int hp_write_key(HP_INFO *info, HP_KEYDEF *keyinfo,
 		 const byte *record, byte *recpos)
@@ -181,18 +204,53 @@ int hp_write_key(HP_INFO *info, HP_KEYDEF *keyinfo,
   halfbuff= (long) share->blength >> 1;
   pos= hp_find_hash(&keyinfo->block,(first_index=share->records-halfbuff));
   
+  /*
+    We're about to add one more hash array position, with hash_mask=#records.
+    The number of hash positions will change and some entries might need to 
+    be relocated to the newly added position. Those entries are currently 
+    members of the list that starts at #first_index position (this is 
+    guaranteed by properties of hp_mask(hp_rec_hashnr(X)) mapping function)
+    At #first_index position currently there may be either:
+    a) An entry with hashnr != first_index. We don't need to move it.
+    or
+    b) A list of items with hash_mask=first_index. The list contains entries
+       of 2 types:
+       1) entries that should be relocated to the list that starts at new 
+          position we're adding ('uppper' list)
+       2) entries that should be left in the list starting at #first_index 
+          position ('lower' list)
+  */
   if (pos != empty)				/* If some records */
   {
     do
     {
       hashnr = hp_rec_hashnr(keyinfo, pos->ptr_to_rec);
-      if (flag == 0)				/* First loop; Check if ok */
+      if (flag == 0)
+      {
+        /* 
+          First loop, bail out if we're dealing with case a) from above 
+          comment
+        */
 	if (hp_mask(hashnr, share->blength, share->records) != first_index)
 	  break;
+      }
+      /*
+        flag & LOWFIND - found a record that should be put into lower position
+        flag & LOWUSED - lower position occupied by the record
+        Same for HIGHFIND and HIGHUSED and 'upper' position
+
+        gpos  - ptr to last element in lower position's list
+        gpos2 - ptr to last element in upper position's list
+
+        ptr_to_rec - ptr to last entry that should go into lower list.
+        ptr_to_rec2 - same for upper list.
+      */
       if (!(hashnr & halfbuff))
-      {						/* Key will not move */
+      {						
+        /* Key should be put into 'lower' list */
 	if (!(flag & LOWFIND))
 	{
+          /* key is the first element to go into lower position */
 	  if (flag & HIGHFIND)
 	  {
 	    flag=LOWFIND | HIGHFIND;
@@ -203,16 +261,21 @@ int hp_write_key(HP_INFO *info, HP_KEYDEF *keyinfo,
 	  }
 	  else
 	  {
-	    flag=LOWFIND | LOWUSED;		/* key isn't changed */
+            /*
+              We can only get here at first iteration: key is at 'lower' 
+              position pos and should be left here.
+            */
+	    flag=LOWFIND | LOWUSED;
 	    gpos=pos;
 	    ptr_to_rec=pos->ptr_to_rec;
 	  }
 	}
 	else
         {
+          /* Already have another key for lower position */
 	  if (!(flag & LOWUSED))
 	  {
-	    /* Change link of previous LOW-key */
+	    /* Change link of previous lower-list key */
 	    gpos->ptr_to_rec=ptr_to_rec;
 	    gpos->next_key=pos;
 	    flag= (flag & HIGHFIND) | (LOWFIND | LOWUSED);
@@ -222,19 +285,21 @@ int hp_write_key(HP_INFO *info, HP_KEYDEF *keyinfo,
 	}
       }
       else
-      {						/* key will be moved */
+      {
+        /* key will be put into 'higher' list */
 	if (!(flag & HIGHFIND))
 	{
 	  flag= (flag & LOWFIND) | HIGHFIND;
 	  /* key shall be moved to the last (empty) position */
-	  gpos2 = empty; empty=pos;
+	  gpos2= empty;
+          empty= pos;
 	  ptr_to_rec2=pos->ptr_to_rec;
 	}
 	else
 	{
 	  if (!(flag & HIGHUSED))
 	  {
-	    /* Change link of previous hash-key and save */
+	    /* Change link of previous upper-list key and save */
 	    gpos2->ptr_to_rec=ptr_to_rec2;
 	    gpos2->next_key=pos;
 	    flag= (flag & LOWFIND) | (HIGHFIND | HIGHUSED);
@@ -246,6 +311,15 @@ int hp_write_key(HP_INFO *info, HP_KEYDEF *keyinfo,
     }
     while ((pos=pos->next_key));
     
+    if ((flag & (LOWFIND | HIGHFIND)) == (LOWFIND | HIGHFIND))
+    {
+      /*
+        If both 'higher' and 'lower' list have at least one element, now
+        there are two hash buckets instead of one.
+      */
+      keyinfo->hash_buckets++;
+    }
+
     if ((flag & (LOWFIND | LOWUSED)) == LOWFIND)
     {
       gpos->ptr_to_rec=ptr_to_rec;
@@ -265,6 +339,7 @@ int hp_write_key(HP_INFO *info, HP_KEYDEF *keyinfo,
   {
     pos->ptr_to_rec=recpos;
     pos->next_key=0;
+    keyinfo->hash_buckets++;
   }
   else
   {
@@ -280,6 +355,7 @@ int hp_write_key(HP_INFO *info, HP_KEYDEF *keyinfo,
     }
     else
     {
+      keyinfo->hash_buckets++;
       pos->ptr_to_rec=recpos;
       pos->next_key=0;
       hp_movelink(pos, gpos, empty);

include/heap.h

@@ -63,18 +63,48 @@ typedef struct st_heap_ptrs
 
 struct st_level_info
 {
-  uint free_ptrs_in_block,records_under_level;
-  HP_PTRS *last_blocks;			/* pointers to HP_PTRS or records */
+  /* Number of unused slots in *last_blocks HP_PTRS block (0 for 0th level) */
+  uint free_ptrs_in_block;
+  
+  /*
+    Maximum number of records that can be 'contained' inside of each element
+    of last_blocks array. For level 0 - 1, for level 1 - HP_PTRS_IN_NOD, for 
+    level 2 - HP_PTRS_IN_NOD^2 and so forth.
+  */
+  uint records_under_level;
+
+  /*
+    Ptr to last allocated HP_PTRS (or records buffer for level 0) on this 
+    level.
+  */
+  HP_PTRS *last_blocks;			
 };
 
-typedef struct st_heap_block		/* The data is saved in blocks */
+
+/*
+  Heap table records and hash index entries are stored in HP_BLOCKs.
+  HP_BLOCK is used as a 'growable array' of fixed-size records. Size of record
+  is recbuffer bytes.
+  The internal representation is as follows:
+  HP_BLOCK is a hierarchical structure of 'blocks'.
+  A block at level 0 is an array records_in_block records. 
+  A block at higher level is an HP_PTRS structure with pointers to blocks at 
+  lower levels.
+  At the highest level there is one top block. It is stored in HP_BLOCK::root.
+
+  See hp_find_block for a description of how record pointer is obtained from 
+  its index.
+  See hp_get_new_block 
+*/
+
+typedef struct st_heap_block
 {
-  HP_PTRS *root;
+  HP_PTRS *root;                        /* Top-level block */ 
   struct st_level_info level_info[HP_MAX_LEVELS+1];
-  uint levels;
-  uint records_in_block;		/* Records in a heap-block */
+  uint levels;                          /* number of used levels */
+  uint records_in_block;		/* Records in one heap-block */
   uint recbuffer;			/* Length of one saved record */
-  ulong last_allocated;			/* Blocks allocated, used by keys */
+  ulong last_allocated; /* number of records there is allocated space for */
 } HP_BLOCK;
 
 struct st_heap_info;			/* For referense */
@@ -87,6 +117,11 @@ typedef struct st_hp_keydef		/* Key definition with open */
   uint8 algorithm;			/* HASH / BTREE */
   HA_KEYSEG *seg;
   HP_BLOCK block;			/* Where keys are saved */
+  /*
+    Number of buckets used in hash table. Used only to provide
+    #records estimates for heap key scans.
+  */
+  ha_rows hash_buckets; 
   TREE rb_tree;
   int (*write_key)(struct st_heap_info *info, struct st_hp_keydef *keyinfo,
 		   const byte *record, byte *recpos);
@@ -102,7 +137,7 @@ typedef struct st_heap_share
   ulong min_records,max_records;	/* Params to open */
   ulong data_length,index_length;
   uint records;				/* records */
-  uint blength;
+  uint blength;				/* records rounded up to 2^n */
   uint deleted;				/* Deleted records in database */
   uint reclength;			/* Length of one record */
   uint changed;

mysql-test/r/heap.result

@@ -4,7 +4,7 @@ insert into t1 values(1,1),(2,2),(3,3),(4,4);
 delete from t1 where a=1 or a=0;
 show keys from t1;
 Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment
-t1	0	PRIMARY	1	a	NULL	NULL	NULL	NULL		HASH	
+t1	0	PRIMARY	1	a	NULL	3	NULL	NULL		HASH	
 select * from t1;
 a	b
 2	2
@@ -169,7 +169,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	btn	NULL	NULL	NULL	11	Using where
 explain select * from t1 where btn="a" and new_col="a";
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ref	btn	btn	11	const,const	10	Using where
+1	SIMPLE	t1	ref	btn	btn	11	const,const	2	Using where
 drop table t1;
 CREATE TABLE t1 (
 a int default NULL,
@@ -182,7 +182,7 @@ SELECT * FROM t1 WHERE a=NULL;
 a	b
 explain SELECT * FROM t1 WHERE a IS NULL;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ref	a	a	5	const	10	Using where
+1	SIMPLE	t1	ref	a	a	5	const	1	Using where
 SELECT * FROM t1 WHERE a<=>NULL;
 a	b
 NULL	99
@@ -204,7 +204,7 @@ key a (a)
 INSERT INTO t1 VALUES (10), (10), (10);
 EXPLAIN SELECT * FROM t1 WHERE a=10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ref	a	a	5	const	10	Using where
+1	SIMPLE	t1	ref	a	a	5	const	3	Using where
 SELECT * FROM t1 WHERE a=10;
 a
 10

mysql-test/r/heap_hash.result

-drop table if exists t1;
+drop table if exists t1,t2;
 create table t1 (a int not null,b int not null, primary key using HASH (a)) engine=heap comment="testing heaps" avg_row_length=100 min_rows=1 max_rows=100;
 insert into t1 values(1,1),(2,2),(3,3),(4,4);
 delete from t1 where a=1 or a=0;
 show keys from t1;
 Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment
-t1	0	PRIMARY	1	a	NULL	NULL	NULL	NULL		HASH	
+t1	0	PRIMARY	1	a	NULL	3	NULL	NULL		HASH	
 select * from t1;
 a	b
 2	2
@@ -169,7 +169,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	btn	NULL	NULL	NULL	11	Using where
 explain select * from t1 where btn="a" and new_col="a";
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ref	btn	btn	11	const,const	10	Using where
+1	SIMPLE	t1	ref	btn	btn	11	const,const	2	Using where
 drop table t1;
 CREATE TABLE t1 (
 a int default NULL,
@@ -182,7 +182,7 @@ SELECT * FROM t1 WHERE a=NULL;
 a	b
 explain SELECT * FROM t1 WHERE a IS NULL;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ref	a	a	5	const	10	Using where
+1	SIMPLE	t1	ref	a	a	5	const	1	Using where
 SELECT * FROM t1 WHERE a<=>NULL;
 a	b
 NULL	99
@@ -203,3 +203,155 @@ DELETE from t1 where a < 100;
 SELECT * from t1;
 a
 DROP TABLE t1;
+create table t1
+(
+a char(8) not null,
+b char(20) not null,
+c int not null,
+key (a)
+) engine=heap;
+insert into t1 values ('aaaa', 'prefill-hash=5',0);
+insert into t1 values ('aaab', 'prefill-hash=0',0);
+insert into t1 values ('aaac', 'prefill-hash=7',0);
+insert into t1 values ('aaad', 'prefill-hash=2',0);
+insert into t1 values ('aaae', 'prefill-hash=1',0);
+insert into t1 values ('aaaf', 'prefill-hash=4',0);
+insert into t1 values ('aaag', 'prefill-hash=3',0);
+insert into t1 values ('aaah', 'prefill-hash=6',0);
+explain select * from t1 where a='aaaa';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+explain select * from t1 where a='aaab';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+explain select * from t1 where a='aaac';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+explain select * from t1 where a='aaad';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+insert into t1 select * from t1;
+explain select * from t1 where a='aaaa';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+explain select * from t1 where a='aaab';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+explain select * from t1 where a='aaac';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+explain select * from t1 where a='aaad';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+flush tables;
+explain select * from t1 where a='aaaa';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	2	Using where
+explain select * from t1 where a='aaab';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	2	Using where
+explain select * from t1 where a='aaac';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	2	Using where
+explain select * from t1 where a='aaad';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	2	Using where
+create table t2 as select * from t1;
+delete from t1;
+insert into t1 select * from t2;
+explain select * from t1 where a='aaaa';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+explain select * from t1 where a='aaab';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+explain select * from t1 where a='aaac';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+explain select * from t1 where a='aaad';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	a	a	8	const	1	Using where
+drop table t1, t2;
+create table t1 (
+id int unsigned not null primary key auto_increment, 
+name varchar(20) not null,
+index heap_idx(name),
+index btree_idx using btree(name)
+) engine=heap;
+create table t2 (
+id int unsigned not null primary key auto_increment, 
+name varchar(20) not null,
+index btree_idx using btree(name),
+index heap_idx(name)
+) engine=heap;
+insert into t1 (name) values ('Matt'), ('Lilu'), ('Corbin'), ('Carly'), 
+('Suzy'), ('Hoppy'), ('Burrito'), ('Mimi'), ('Sherry'), ('Ben'), ('Phil'), 
+('Emily'), ('Mike');
+insert into t2 select * from t1;
+explain select * from t1 where name='matt';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	heap_idx,btree_idx	heap_idx	20	const	1	Using where
+explain select * from t2 where name='matt';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ref	btree_idx,heap_idx	btree_idx	20	const	1	Using where
+explain select * from t1 where name='Lilu';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	heap_idx,btree_idx	heap_idx	20	const	1	Using where
+explain select * from t2 where name='Lilu';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ref	btree_idx,heap_idx	btree_idx	20	const	1	Using where
+explain select * from t1 where name='Phil';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	heap_idx,btree_idx	heap_idx	20	const	1	Using where
+explain select * from t2 where name='Phil';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ref	btree_idx,heap_idx	btree_idx	20	const	1	Using where
+explain select * from t1 where name='Lilu';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	heap_idx,btree_idx	heap_idx	20	const	1	Using where
+explain select * from t2 where name='Lilu';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ref	btree_idx,heap_idx	btree_idx	20	const	1	Using where
+insert into t1 (name) select name from t2;
+insert into t1 (name) select name from t2;
+insert into t1 (name) select name from t2;
+insert into t1 (name) select name from t2;
+insert into t1 (name) select name from t2;
+insert into t1 (name) select name from t2;
+flush tables;
+select count(*) from t1 where name='Matt';
+count(*)
+7
+explain select * from t1 ignore index (btree_idx) where name='matt';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	heap_idx	heap_idx	20	const	7	Using where
+show index from t1;
+Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment
+t1	0	PRIMARY	1	id	NULL	91	NULL	NULL		HASH	
+t1	1	heap_idx	1	name	NULL	13	NULL	NULL		HASH	
+t1	1	btree_idx	1	name	A	NULL	NULL	NULL		BTREE	
+show index from t1;
+Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment
+t1	0	PRIMARY	1	id	NULL	91	NULL	NULL		HASH	
+t1	1	heap_idx	1	name	NULL	13	NULL	NULL		HASH	
+t1	1	btree_idx	1	name	A	NULL	NULL	NULL		BTREE	
+create table t3
+(
+a varchar(20) not null,
+b varchar(20) not null,
+key (a,b)
+) engine=heap;
+insert into t3 select name, name from t1;
+show index from t3;
+Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment
+t3	1	a	1	a	NULL	NULL	NULL	NULL		HASH	
+t3	1	a	2	b	NULL	15	NULL	NULL		HASH	
+show index from t3;
+Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment
+t3	1	a	1	a	NULL	NULL	NULL	NULL		HASH	
+t3	1	a	2	b	NULL	15	NULL	NULL		HASH	
+explain select * from t1 ignore key(btree_idx), t3 where t1.name='matt' and t3.a = concat('',t1.name) and t3.b=t1.name;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	heap_idx	heap_idx	20	const	7	Using where
+1	SIMPLE	t3	ref	a	a	40	func,const	6	Using where
+drop table t1, t2, t3;

mysql-test/r/myisam.result

@@ -543,7 +543,7 @@ Warnings:
 Note	1031	Table storage engine for 't1' doesn't have this option
 show keys from t1;
 Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment
-t1	1	a	1	a	NULL	NULL	NULL	NULL	YES	HASH	
+t1	1	a	1	a	NULL	1000	NULL	NULL	YES	HASH	
 drop table t1,t2;
 create table t1 ( a tinytext, b char(1), index idx (a(1),b) );
 insert into t1 values (null,''), (null,'');

mysql-test/t/heap_hash.test

@@ -3,7 +3,7 @@
 #
 
 --disable_warnings
-drop table if exists t1;
+drop table if exists t1,t2;
 --enable_warnings
 
 create table t1 (a int not null,b int not null, primary key using HASH (a)) engine=heap comment="testing heaps" avg_row_length=100 min_rows=1 max_rows=100;
@@ -141,3 +141,113 @@ INSERT into t1 values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10),(11);
 DELETE from t1 where a < 100;
 SELECT * from t1;
 DROP TABLE t1;
+
+
+#
+# Hash index # records estimate test
+#
+create table t1
+(
+  a char(8) not null,
+  b char(20) not null,
+  c int not null,
+  key (a)
+) engine=heap;
+
+insert into t1 values ('aaaa', 'prefill-hash=5',0);
+insert into t1 values ('aaab', 'prefill-hash=0',0);
+insert into t1 values ('aaac', 'prefill-hash=7',0);
+insert into t1 values ('aaad', 'prefill-hash=2',0);
+insert into t1 values ('aaae', 'prefill-hash=1',0);
+insert into t1 values ('aaaf', 'prefill-hash=4',0);
+insert into t1 values ('aaag', 'prefill-hash=3',0);
+insert into t1 values ('aaah', 'prefill-hash=6',0);
+
+explain select * from t1 where a='aaaa';
+explain select * from t1 where a='aaab';
+explain select * from t1 where a='aaac';
+explain select * from t1 where a='aaad';
+insert into t1 select * from t1;
+
+explain select * from t1 where a='aaaa';
+explain select * from t1 where a='aaab';
+explain select * from t1 where a='aaac';
+explain select * from t1 where a='aaad';
+
+# a known effect: table reload causes statistics to be updated:
+flush tables;
+explain select * from t1 where a='aaaa';
+explain select * from t1 where a='aaab';
+explain select * from t1 where a='aaac';
+explain select * from t1 where a='aaad';
+
+# Check if delete_all_rows() updates #hash_buckets
+create table t2 as select * from t1;
+delete from t1;
+insert into t1 select * from t2;
+explain select * from t1 where a='aaaa';
+explain select * from t1 where a='aaab';
+explain select * from t1 where a='aaac';
+explain select * from t1 where a='aaad';
+drop table t1, t2;
+
+
+# Btree and hash index use costs. 
+create table t1 (
+  id int unsigned not null primary key auto_increment, 
+  name varchar(20) not null,
+  index heap_idx(name),
+  index btree_idx using btree(name)
+) engine=heap;
+
+create table t2 (
+  id int unsigned not null primary key auto_increment, 
+  name varchar(20) not null,
+  index btree_idx using btree(name),
+  index heap_idx(name)
+) engine=heap;
+
+insert into t1 (name) values ('Matt'), ('Lilu'), ('Corbin'), ('Carly'), 
+  ('Suzy'), ('Hoppy'), ('Burrito'), ('Mimi'), ('Sherry'), ('Ben'), ('Phil'), 
+  ('Emily'), ('Mike');
+insert into t2 select * from t1;
+explain select * from t1 where name='matt';
+explain select * from t2 where name='matt';
+
+explain select * from t1 where name='Lilu';
+explain select * from t2 where name='Lilu';
+
+explain select * from t1 where name='Phil';
+explain select * from t2 where name='Phil';
+
+explain select * from t1 where name='Lilu';
+explain select * from t2 where name='Lilu';
+
+insert into t1 (name) select name from t2;
+insert into t1 (name) select name from t2;
+insert into t1 (name) select name from t2;
+insert into t1 (name) select name from t2;
+insert into t1 (name) select name from t2;
+insert into t1 (name) select name from t2;
+flush tables;
+select count(*) from t1 where name='Matt';
+explain select * from t1 ignore index (btree_idx) where name='matt';
+show index from t1;
+
+show index from t1;
+
+create table t3
+(
+  a varchar(20) not null,
+  b varchar(20) not null,
+  key (a,b)
+) engine=heap;
+insert into t3 select name, name from t1;
+show index from t3;
+show index from t3;
+
+# test rec_per_key use for joins.
+explain select * from t1 ignore key(btree_idx), t3 where t1.name='matt' and t3.a = concat('',t1.name) and t3.b=t1.name;
+
+drop table t1, t2, t3;
+

sql/ha_heap.cc

@@ -30,6 +30,18 @@
 const char **ha_heap::bas_ext() const
 { static const char *ext[1]= { NullS }; return ext; }
 
+/*
+  Hash index statistics is updated (copied from HP_KEYDEF::hash_buckets to 
+  rec_per_key) after 1/HEAP_STATS_UPDATE_THRESHOLD fraction of table records 
+  have been inserted/updated/deleted. delete_all_rows() and table flush cause 
+  immediate update.
+
+  NOTE
+   hash index statistics must be updated when number of table records changes
+   from 0 to non-zero value and vice versa. Otherwise records_in_range may 
+   erroneously return 0 and 'range' may miss records.
+*/
+#define HEAP_STATS_UPDATE_THRESHOLD 10
 
 int ha_heap::open(const char *name, int mode, uint test_if_locked)
 {
@@ -48,6 +60,8 @@ int ha_heap::open(const char *name, int mode, uint test_if_locked)
   {
     /* Initialize variables for the opened table */
     set_keys_for_scanning();
+    if (table->tmp_table == NO_TMP_TABLE)
+      update_key_stats();
   }
   return (file ? 0 : 1);
 }
@@ -84,28 +98,58 @@ void ha_heap::set_keys_for_scanning(void)
   }
 }
 
+void ha_heap::update_key_stats()
+{
+  for (uint i= 0; i < table->keys; i++)
+  {
+    KEY *key=table->key_info+i;
+    if (key->algorithm != HA_KEY_ALG_BTREE)
+    {
+      ha_rows hash_buckets= file->s->keydef[i].hash_buckets;
+      key->rec_per_key[key->key_parts-1]= 
+        hash_buckets ? file->s->records/hash_buckets : 0;
+    }
+  }
+  records_changed= 0;
+}
+
 int ha_heap::write_row(byte * buf)
 {
+  int res;
   statistic_increment(ha_write_count,&LOCK_status);
   if (table->timestamp_field_type & TIMESTAMP_AUTO_SET_ON_INSERT)
     table->timestamp_field->set_time();
   if (table->next_number_field && buf == table->record[0])
     update_auto_increment();
-  return heap_write(file,buf);
+  res= heap_write(file,buf);
+  if (!res && table->tmp_table == NO_TMP_TABLE && 
+      ++records_changed*HEAP_STATS_UPDATE_THRESHOLD > file->s->records)
+    update_key_stats();
+  return res;
 }
 
 int ha_heap::update_row(const byte * old_data, byte * new_data)
 {
+  int res;
   statistic_increment(ha_update_count,&LOCK_status);
   if (table->timestamp_field_type & TIMESTAMP_AUTO_SET_ON_UPDATE)
     table->timestamp_field->set_time();
-  return heap_update(file,old_data,new_data);
+  res= heap_update(file,old_data,new_data);
+  if (!res && table->tmp_table == NO_TMP_TABLE && 
+      ++records_changed*HEAP_STATS_UPDATE_THRESHOLD > file->s->records)
+    update_key_stats();
+  return res;
 }
 
 int ha_heap::delete_row(const byte * buf)
 {
+  int res;
   statistic_increment(ha_delete_count,&LOCK_status);
-  return heap_delete(file,buf);
+  res= heap_delete(file,buf);
+  if (!res && table->tmp_table == NO_TMP_TABLE && 
+      ++records_changed*HEAP_STATS_UPDATE_THRESHOLD > file->s->records)
+    update_key_stats();
+  return res;
 }
 
 int ha_heap::index_read(byte * buf, const byte * key, uint key_len,
@@ -227,6 +271,8 @@ int ha_heap::extra(enum ha_extra_function operation)
 int ha_heap::delete_all_rows()
 {
   heap_clear(file);
+  if (table->tmp_table == NO_TMP_TABLE)
+    update_key_stats();
   return 0;
 }
 
@@ -384,7 +430,8 @@ ha_rows ha_heap::records_in_range(uint inx, key_range *min_key,
       min_key->flag != HA_READ_KEY_EXACT ||
       max_key->flag != HA_READ_AFTER_KEY)
     return HA_POS_ERROR;			// Can only use exact keys
-  return 10;					// Good guess
+  else
+    return key->rec_per_key[key->key_parts-1];
 }
 
 

sql/ha_heap.h

@@ -27,9 +27,10 @@ class ha_heap: public handler
 {
   HP_INFO *file;
   key_map btree_keys;
-
- public:
-  ha_heap(TABLE *table): handler(table), file(0) {}
+  /* number of records changed since last statistics update */
+  uint    records_changed;
+public:
+  ha_heap(TABLE *table): handler(table), file(0), records_changed(0) {}
   ~ha_heap() {}
   const char *table_type() const { return "HEAP"; }
   const char *index_type(uint inx)
@@ -91,5 +92,6 @@ class ha_heap: public handler
 
   THR_LOCK_DATA **store_lock(THD *thd, THR_LOCK_DATA **to,
 			     enum thr_lock_type lock_type);
-
+private:
+  void update_key_stats();
 };

sql/structs.h

@@ -89,7 +89,12 @@ typedef struct st_key {
   enum  ha_key_alg algorithm;
   KEY_PART_INFO *key_part;
   char	*name;				/* Name of key */
-  ulong *rec_per_key;			/* Key part distribution */
+  /*
+    Array of AVG(#records with the same field value) for 1st ... Nth key part.
+    0 means 'not known'.
+    For temporary heap tables this member is NULL.
+  */
+  ulong *rec_per_key;
   union {
     int  bdb_return_if_eq;
   } handler;