Fixed bug #19079.

The bug caused a reported index corruption in the cases when
key_cache_block_size was not a multiple of myisam_block_size,
e.g. when key_cache_block_size=1536 while myisam_block_size=1024.

mysql-test/r/key_cache.result

@@ -287,3 +287,45 @@ check table t1;
 Table	Op	Msg_type	Msg_text
 test.t1	check	status	OK
 drop table t1;
+CREATE TABLE t1(a int NOT NULL AUTO_INCREMENT PRIMARY KEY);
+SET GLOBAL key_cache_block_size=1536;
+INSERT INTO t1 VALUES (1);
+SELECT @@key_cache_block_size;
+@@key_cache_block_size
+1536
+CHECK TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	check	status	OK
+DROP TABLE t1;
+CREATE TABLE t1(a int NOT NULL AUTO_INCREMENT PRIMARY KEY, b int);
+CREATE TABLE t2(a int NOT NULL AUTO_INCREMENT PRIMARY KEY, b int);
+SET GLOBAL key_cache_block_size=1536;
+INSERT INTO t1 VALUES (1,0);
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+SELECT COUNT(*) FROM t1;
+COUNT(*)
+4181
+SELECT @@key_cache_block_size;
+@@key_cache_block_size
+1536
+CHECK TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	check	status	OK
+DROP TABLE t1,t2;

mysql-test/t/key_cache.test

@@ -149,6 +149,7 @@ show status like 'key_blocks_used';
 --replace_result 1812 KEY_BLOCKS_UNUSED 1793 KEY_BLOCKS_UNUSED 1674 KEY_BLOCKS_UNUSED 1818 KEY_BLOCKS_UNUSED 1824 KEY_BLOCKS_UNUSED
 show status like 'key_blocks_unused';
 
+
 # Cleanup
 # We don't reset keycache2 as we want to ensure that mysqld will reset it
 set global keycache2.key_buffer_size=0;
@@ -157,7 +158,7 @@ set global keycache2.key_buffer_size=0;
 set global keycache3.key_buffer_size=100;
 set global keycache3.key_buffer_size=0;
 
-# Test case for buf 6447
+# Test case for bug 6447
 
 create table t1 (mytext text, FULLTEXT (mytext));
 insert t1 values ('aaabbb');
@@ -168,4 +169,42 @@ check table t1;
 
 drop table t1;
 
+#
+# Bug #19079: corrupted index when key_cache_block_size is not multiple of
+#             myisam_block_size
+
+CREATE TABLE t1(a int NOT NULL AUTO_INCREMENT PRIMARY KEY);
+SET GLOBAL key_cache_block_size=1536;
+INSERT INTO t1 VALUES (1);
+SELECT @@key_cache_block_size;
+CHECK TABLE t1;
+DROP TABLE t1;
+
+CREATE TABLE t1(a int NOT NULL AUTO_INCREMENT PRIMARY KEY, b int);
+CREATE TABLE t2(a int NOT NULL AUTO_INCREMENT PRIMARY KEY, b int);
+SET GLOBAL key_cache_block_size=1536;
+INSERT INTO t1 VALUES (1,0);
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+INSERT INTO t2(b) SELECT b FROM t1;
+INSERT INTO t1(b) SELECT b FROM t2;
+SELECT COUNT(*) FROM t1;
+SELECT @@key_cache_block_size;
+CHECK TABLE t1;
+DROP TABLE t1,t2;
+
 # End of 4.1 tests

mysys/mf_keycache.c

@@ -1741,6 +1741,7 @@ byte *key_cache_read(KEY_CACHE *keycache,
     uint status;
     int page_st;
 
+    offset= (uint) (filepos & (keycache->key_cache_block_size-1));
     /* Read data in key_cache_block_size increments */
     do
     {
@@ -1750,7 +1751,6 @@ byte *key_cache_read(KEY_CACHE *keycache,
 	keycache_pthread_mutex_unlock(&keycache->cache_lock);
 	goto no_key_cache;
       }
-      offset= (uint) (filepos & (keycache->key_cache_block_size-1));
       filepos-= offset;
       read_length= length;
       set_if_smaller(read_length, keycache->key_cache_block_size-offset);
@@ -1826,6 +1826,7 @@ byte *key_cache_read(KEY_CACHE *keycache,
 #endif
       buff+= read_length;
       filepos+= read_length+offset;
+      offset= 0;
 
     } while ((length-= read_length));
     DBUG_RETURN(start);
@@ -1877,17 +1878,17 @@ int key_cache_insert(KEY_CACHE *keycache,
     uint read_length;
     int page_st;
     int error;
+    uint offset;
 
+    offset= (uint) (filepos & (keycache->key_cache_block_size-1));
     do
     {
-      uint offset;
       keycache_pthread_mutex_lock(&keycache->cache_lock);
       if (!keycache->can_be_used)
       {
 	keycache_pthread_mutex_unlock(&keycache->cache_lock);
 	DBUG_RETURN(0);
       }
-      offset= (uint) (filepos & (keycache->key_cache_block_size-1));
       /* Read data into key cache from buff in key_cache_block_size incr. */
       filepos-= offset;
       read_length= length;
@@ -1945,6 +1946,7 @@ int key_cache_insert(KEY_CACHE *keycache,
 
       buff+= read_length;
       filepos+= read_length+offset;
+      offset= 0;
 
     } while ((length-= read_length));
   }
@@ -2011,17 +2013,17 @@ int key_cache_write(KEY_CACHE *keycache,
     /* Key cache is used */
     uint read_length;
     int page_st;
+    uint offset;
 
+    offset= (uint) (filepos & (keycache->key_cache_block_size-1));
     do
     {
-      uint offset;
       keycache_pthread_mutex_lock(&keycache->cache_lock);
       if (!keycache->can_be_used)
       {
 	keycache_pthread_mutex_unlock(&keycache->cache_lock);
 	goto no_key_cache;
       }
-      offset= (uint) (filepos & (keycache->key_cache_block_size-1));
       /* Write data in key_cache_block_size increments */
       filepos-= offset;
       read_length= length;