WL#1700 - Properly count key_blocks_used and key_blocks_current.

Introduced a new free blocks list. Free blocks are now re-used before
new blocks are allocated from the pool. There is a new status variable 
which can be queried by "show status like key_blocks_unused".


include/keycache.h:
  WL#1700 - Properly count key_blocks_used and key_blocks_current.
  free_block_list is the new free blocks list. It is implemented like a stack (LIFO).
  blocks_unused holds the number of never used blocks plus the number of blocks in the free list.
  Removed the variable global_blocks_used, as it was always the same as blocks_used.
mysql-test/r/key_cache.result:
  WL#1700 - Properly count key_blocks_used and key_blocks_current.
  Inserted some commands which show how key_blocks_used and key_blocks_unused work.
mysql-test/t/key_cache.test:
  WL#1700 - Properly count key_blocks_used and key_blocks_current.
  Inserted some commands which show how key_blocks_used and key_blocks_unused work.
mysys/mf_keycache.c:
  WL#1700 - Properly count key_blocks_used and key_blocks_current.
  Introduced a new free blocks list. The introductory comment says it all (I hope).
  Removed the variable global_blocks_used, as it was always the same as blocks_used.
sql/mysqld.cc:
  WL#1700 - Properly count key_blocks_used and key_blocks_current.
  The blocks_unused count can be queried by "show status like key_blocks_unused".
  Removed the variable global_blocks_used, as it was always the same as blocks_used.
  Introduced SHOW_KEY_CACHE_CONST_LONG for status variables that
  must not be modified (i.e. flushed to zero).
sql/sql_show.cc:
  WL#1700 - Properly count key_blocks_used and key_blocks_current.
  Introduced SHOW_KEY_CACHE_CONST_LONG for status variables that
  must not be modified (i.e. flushed to zero).
sql/sql_test.cc:
  WL#1700 - Properly count key_blocks_used and key_blocks_current.
  Removed the variable global_blocks_used, as it was always the same as blocks_used.
sql/structs.h:
  WL#1700 - Properly count key_blocks_used and key_blocks_current.
  Introduced SHOW_KEY_CACHE_CONST_LONG for status variables that
  must not be modified (i.e. flushed to zero).

1 files changed, 3 insertions, 2 deletions

diff --git a/include/keycache.h b/include/keycache.h
index b882f3127f5..26ee0ccadb1 100644
--- a/include/keycache.h
+++ b/include/keycache.h
@@ -57,7 +57,8 @@ typedef struct st_key_cache
   int hash_links;                /* max number of hash links                 */
   int hash_links_used;           /* number of hash links currently used      */
   int disk_blocks;               /* max number of blocks in the cache        */
-  ulong blocks_used;             /* number of currently used blocks          */
+  ulong blocks_used; /* maximum number of concurrently used blocks */
+  ulong blocks_unused; /* number of currently unused blocks */
   ulong blocks_changed;          /* number of currently dirty blocks         */
   ulong warm_blocks;             /* number of blocks in warm sub-chain       */
   ulong cnt_for_resize_op;       /* counter to block resize operation        */
@@ -65,6 +66,7 @@ typedef struct st_key_cache
   HASH_LINK **hash_root;         /* arr. of entries into hash table buckets  */
   HASH_LINK *hash_link_root;     /* memory for hash table links              */
   HASH_LINK *free_hash_list;     /* list of free hash links                  */
+  BLOCK_LINK *free_block_list; /* list of free blocks */
   BLOCK_LINK *block_root;        /* memory for block links                   */
   byte HUGE_PTR *block_mem;      /* memory for block buffers                 */
   BLOCK_LINK *used_last;         /* ptr to the last block of the LRU chain   */
@@ -87,7 +89,6 @@ typedef struct st_key_cache
   ulong param_age_threshold;    /* determines when hot block is downgraded  */
 
   /* Statistics variables */
-  ulong global_blocks_used;	/* number of currently used blocks          */
   ulong global_blocks_changed;	/* number of currently dirty blocks         */
   ulong global_cache_w_requests;/* number of write requests (write hits)    */
   ulong global_cache_write;     /* number of writes from the cache to files */