Bug#40675 MySQL 5.1 crash with index merge algorithm and Merge tables

            
A Query in the MyISAM merge table was crashing 
if the index merge algorithm was being used

Index Merge optimization requires the reading of 
multiple indexes at the same time. Reading multiple 
indexes at once with current SE API means that we 
need to have handler instance for each to-be-read 
index. This is done by creating clones of the handlers 
instances. The clone internally does a open of the handler.

The open for a MERGE engine is handled in the following 
phases

1) open parent table
2) generate list of underlying
   table
3) attach underlying tables

But the current implementation does only the first 
phase (i.e.) open parent table.

The current patch fixes this at the MERGE engine level, 
by handling the clone operation within the MERGE engine 
rather than in the storage engine API. It opens and 
attaches the MyISAM tables on the MyISAM storage engine 
interface directly within the MERGE engine. The new MyISAM 
table instances, as well as the MERGE clone itself, are not 
visible in the table cache. This is not a problem because
all locking is handled by the original MERGE table from which
this is cloned of.

mysql-test/r/merge.result

@@ -2025,7 +2025,6 @@ TABLE_SCHEMA = 'test' and TABLE_NAME='tm1';
 TABLE_CATALOG	TABLE_SCHEMA	TABLE_NAME	TABLE_TYPE	ENGINE	VERSION	ROW_FORMAT	TABLE_ROWS	AVG_ROW_LENGTH	DATA_LENGTH	MAX_DATA_LENGTH	INDEX_LENGTH	DATA_FREE	AUTO_INCREMENT	CREATE_TIME	UPDATE_TIME	CHECK_TIME	TABLE_COLLATION	CHECKSUM	CREATE_OPTIONS	TABLE_COMMENT
 NULL	test	tm1	BASE TABLE	NULL	NULL	NULL	#	#	#	#	#	#	#	#	#	#	NULL	#	#	Unable to open underlying table which is differently defined or of non-MyISAM ty
 DROP TABLE tm1;
-End of 5.1 tests
 CREATE TABLE t1(C1 INT, C2 INT, KEY C1(C1), KEY C2(C2)) ENGINE=MYISAM;
 CREATE TABLE t2(C1 INT, C2 INT, KEY C1(C1), KEY C2(C2)) ENGINE=MYISAM;
 CREATE TABLE t3(C1 INT, C2 INT, KEY C1(C1), KEY C2(C2)) ENGINE=MYISAM;
@@ -2041,4 +2040,48 @@ EXPLAIN SELECT COUNT(*) FROM t4;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 DROP TABLE t1, t2, t3, t4;
+#
+# Bug #40675 MySQL 5.1 crash with index merge algorithm and Merge tables
+#
+# create MYISAM table t1 and insert values into it
+CREATE TABLE t1(a INT);
+INSERT INTO t1 VALUES(1);
+# create MYISAM table t2 and insert values into it
+CREATE TABLE t2(a INT, b INT, dummy CHAR(16) DEFAULT '', KEY(a), KEY(b));
+INSERT INTO t2(a,b) VALUES
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(1,2);
+# Create the merge table t3
+CREATE TABLE t3(a INT, b INT, dummy CHAR(16) DEFAULT '', KEY(a), KEY(b))
+ENGINE=MERGE UNION=(t2) INSERT_METHOD=FIRST;
+# Lock tables t1 and t3 for write
+LOCK TABLES t1 WRITE, t3 WRITE;
+# Insert values into the merge table t3
+INSERT INTO t3(a,b) VALUES(1,2);
+# select from the join of t2 and t3 (The merge table)
+SELECT t3.a FROM t1,t3 WHERE t3.b=2 AND t3.a=1;
+a
+1
+1
+# Unlock the tables
+UNLOCK TABLES;
+# drop the created tables
+DROP TABLE t1, t2, t3;
 End of 5.1 tests

mysql-test/t/merge.test

@@ -1418,8 +1418,6 @@ TABLE_SCHEMA = 'test' and TABLE_NAME='tm1';
 
 DROP TABLE tm1;
 
---echo End of 5.1 tests
-
 #
 # Bug#36006 - Optimizer does table scan for select count(*)
 #
@@ -1435,4 +1433,54 @@ EXPLAIN SELECT COUNT(*) FROM t1;
 EXPLAIN SELECT COUNT(*) FROM t4;
 DROP TABLE t1, t2, t3, t4;
 
+--echo #
+--echo # Bug #40675 MySQL 5.1 crash with index merge algorithm and Merge tables
+--echo #
+
+--echo # create MYISAM table t1 and insert values into it
+CREATE TABLE t1(a INT);
+INSERT INTO t1 VALUES(1);
+
+--echo # create MYISAM table t2 and insert values into it
+CREATE TABLE t2(a INT, b INT, dummy CHAR(16) DEFAULT '', KEY(a), KEY(b));
+INSERT INTO t2(a,b) VALUES
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),
+(1,2);
+
+--echo # Create the merge table t3
+CREATE TABLE t3(a INT, b INT, dummy CHAR(16) DEFAULT '', KEY(a), KEY(b))
+ENGINE=MERGE UNION=(t2) INSERT_METHOD=FIRST;
+
+--echo # Lock tables t1 and t3 for write
+LOCK TABLES t1 WRITE, t3 WRITE;
+
+--echo # Insert values into the merge table t3
+INSERT INTO t3(a,b) VALUES(1,2);
+
+--echo # select from the join of t2 and t3 (The merge table)
+SELECT t3.a FROM t1,t3 WHERE t3.b=2 AND t3.a=1;
+
+--echo # Unlock the tables
+UNLOCK TABLES;
+
+--echo # drop the created tables
+DROP TABLE t1, t2, t3;
+
 --echo End of 5.1 tests

storage/myisammrg/ha_myisammrg.cc

@@ -116,7 +116,7 @@ static handler *myisammrg_create_handler(handlerton *hton,
 */
 
 ha_myisammrg::ha_myisammrg(handlerton *hton, TABLE_SHARE *table_arg)
-  :handler(hton, table_arg), file(0)
+  :handler(hton, table_arg), file(0), is_cloned(0)
 {}
 
 
@@ -413,7 +413,28 @@ int ha_myisammrg::open(const char *name, int mode __attribute__((unused)),
 
   /* retrieve children table list. */
   my_errno= 0;
-  if (!(file= myrg_parent_open(name, myisammrg_parent_open_callback, this)))
+  if (is_cloned)
+  {
+    /*
+      Open and attaches the MyISAM tables,that are under the MERGE table 
+      parent, on the MyISAM storage engine interface directly within the
+      MERGE engine. The new MyISAM table instances, as well as the MERGE 
+      clone itself, are not visible in the table cache. This is not a 
+      problem because all locking is handled by the original MERGE table
+      from which this is cloned of.
+    */
+    if (!(file= myrg_open(table->s->normalized_path.str, table->db_stat, 
+                                       HA_OPEN_IGNORE_IF_LOCKED)))
+    {
+      DBUG_PRINT("error", ("my_errno %d", my_errno));
+      DBUG_RETURN(my_errno ? my_errno : -1); 
+    }
+
+    file->children_attached= TRUE;
+
+    info(HA_STATUS_NO_LOCK | HA_STATUS_VARIABLE | HA_STATUS_CONST);
+  }
+  else if (!(file= myrg_parent_open(name, myisammrg_parent_open_callback, this)))
   {
     DBUG_PRINT("error", ("my_errno %d", my_errno));
     DBUG_RETURN(my_errno ? my_errno : -1);
@@ -422,6 +443,55 @@ int ha_myisammrg::open(const char *name, int mode __attribute__((unused)),
   DBUG_RETURN(0);
 }
 
+/**
+   Returns a cloned instance of the current handler.
+
+   @return A cloned handler instance.
+ */
+handler *ha_myisammrg::clone(MEM_ROOT *mem_root)
+{
+  MYRG_TABLE    *u_table,*newu_table;
+  ha_myisammrg *new_handler= 
+    (ha_myisammrg*) get_new_handler(table->s, mem_root, table->s->db_type());
+  if (!new_handler)
+    return NULL;
+  
+  /* Inform ha_myisammrg::open() that it is a cloned handler */
+  new_handler->is_cloned= TRUE;
+  /*
+    Allocate handler->ref here because otherwise ha_open will allocate it
+    on this->table->mem_root and we will not be able to reclaim that memory 
+    when the clone handler object is destroyed.
+  */
+  if (!(new_handler->ref= (uchar*) alloc_root(mem_root, ALIGN_SIZE(ref_length)*2)))
+  {
+    delete new_handler;
+    return NULL;
+  }
+
+  if (new_handler->ha_open(table, table->s->normalized_path.str, table->db_stat,
+                            HA_OPEN_IGNORE_IF_LOCKED))
+  {
+    delete new_handler;
+    return NULL;
+  }
+ 
+  /*
+    Iterate through the original child tables and
+    copy the state into the cloned child tables.
+    We need to do this because all the child tables
+    can be involved in delete.
+  */
+  newu_table= new_handler->file->open_tables;
+  for (u_table= file->open_tables; u_table < file->end_table; u_table++)
+  {
+    newu_table->table->state= u_table->table->state;
+    newu_table++;
+  }
+
+  return new_handler;
+ }
+
 
 /**
   @brief Attach children to a MERGE table.
@@ -613,9 +683,10 @@ int ha_myisammrg::close(void)
   DBUG_ENTER("ha_myisammrg::close");
   /*
     Children must not be attached here. Unless the MERGE table has no
-    children. In this case children_attached is always true.
+    children or the handler instance has been cloned. In these cases 
+    children_attached is always true. 
   */
-  DBUG_ASSERT(!this->file->children_attached || !this->file->tables);
+  DBUG_ASSERT(!this->file->children_attached || !this->file->tables || this->is_cloned);
   rc= myrg_close(file);
   file= 0;
   DBUG_RETURN(rc);

storage/myisammrg/ha_myisammrg.h

@@ -25,6 +25,7 @@
 class ha_myisammrg: public handler
 {
   MYRG_INFO *file;
+  my_bool is_cloned;                    /* This instance has been cloned */
 
  public:
   TABLE_LIST    *next_child_attach;     /* next child to attach */
@@ -60,6 +61,7 @@ class ha_myisammrg: public handler
   int open(const char *name, int mode, uint test_if_locked);
   int attach_children(void);
   int detach_children(void);
+  virtual handler *clone(MEM_ROOT *mem_root);
   int close(void);
   int write_row(uchar * buf);
   int update_row(const uchar * old_data, uchar * new_data);

storage/myisammrg/myrg_open.c

@@ -33,7 +33,6 @@
         myrg_attach_children(). Please duplicate changes in these
         functions or make common sub-functions.
 */
-/* purecov: begin deadcode */ /* not used in MySQL server */
 
 MYRG_INFO *myrg_open(const char *name, int mode, int handle_locking)
 {
@@ -198,7 +197,6 @@ err:
   my_errno=save_errno;
   DBUG_RETURN (NULL);
 }
-/* purecov: end */
 
 
 /**