branches/zip: Make innodb_adaptive_hash_index settable.

btr_search_disabled: Rename to btr_search_enabled and change the type
to char, so that it can be directly linked to the MySQL parameters.
Note that the variable is protected by btr_search_latch and
btr_search_enabled_mutex, a new mutex introduced in this patch.

btr_search_enabled_mutex: A new mutex, to protect btr_search_enabled
together with btr_search_latch.

buf_pool_drop_hash_index(): New function, to be called from
btr_search_disable().

btr_search_disable(), btr_search_enable(): Fix bugs.  These functions
were previously unused.

btr_search_guess_on_hash(), btr_search_build_page_hash_index():
Check btr_search_enabled once more, while holding btr_search_latch.

btr_cur_search_to_nth_level(): Note that the reads of btr_search_enabled
may be dirty and explain why it should not be a problem.

innobase_adaptive_hash_index: Remove. The variable btr_search_enabled will be used directly instead.

innodb_adaptive_hash_index_update(): New function, an update callback for
innodb_adaptive_hash_index.  This will call either btr_search_disable()
or btr_search_enable() when the value is assigned.  The functions will
be called even if the value does not appear to be changed, e.g., when
setting from TRUE to TRUE or FALSE to FALSE.

rb://85 approved by Heikki Tuuri.  This addresses Issue #163.

btr/btr0cur.c

@@ -371,7 +371,10 @@ btr_cur_search_to_nth_level(
 #ifdef PAGE_CUR_LE_OR_EXTENDS
 	    && mode != PAGE_CUR_LE_OR_EXTENDS
 #endif /* PAGE_CUR_LE_OR_EXTENDS */
-	    && !UNIV_UNLIKELY(btr_search_disabled)
+	    /* If !has_search_latch, we do a dirty read of
+	    btr_search_enabled below, and btr_search_guess_on_hash()
+	    will have to check it again. */
+	    && UNIV_LIKELY(btr_search_enabled)
 	    && btr_search_guess_on_hash(index, info, tuple, mode,
 					latch_mode, cursor,
 					has_search_latch, mtr)) {
@@ -608,7 +611,11 @@ retry_page_get:
 		cursor->up_bytes = up_bytes;
 
 #ifdef BTR_CUR_ADAPT
-		if (!UNIV_UNLIKELY(btr_search_disabled)) {
+		/* We do a dirty read of btr_search_enabled here.  We
+		will properly check btr_search_enabled again in
+		btr_search_build_page_hash_index() before building a
+		page hash index, while holding btr_search_latch. */
+		if (UNIV_LIKELY(btr_search_enabled)) {
 
 			btr_search_info_update(index, cursor);
 		}

btr/btr0sea.c

@@ -19,8 +19,11 @@ Created 2/17/1996 Heikki Tuuri
 #include "btr0btr.h"
 #include "ha0ha.h"
 
-/* Flag: has the search system been disabled? */
-UNIV_INTERN ibool		btr_search_disabled	= FALSE;
+/* Flag: has the search system been enabled?
+Protected by btr_search_latch and btr_search_enabled_mutex. */
+UNIV_INTERN char		btr_search_enabled	= TRUE;
+
+static mutex_t			btr_search_enabled_mutex;
 
 /* A dummy variable to fool the compiler */
 UNIV_INTERN ulint		btr_search_this_is_zero = 0;
@@ -139,11 +142,11 @@ btr_search_sys_create(
 	btr_search_latch_temp = mem_alloc(sizeof(rw_lock_t));
 
 	rw_lock_create(&btr_search_latch, SYNC_SEARCH_SYS);
+	mutex_create(&btr_search_enabled_mutex, SYNC_SEARCH_SYS_CONF);
 
 	btr_search_sys = mem_alloc(sizeof(btr_search_sys_t));
 
 	btr_search_sys->hash_index = ha_create(hash_size, 0, 0);
-
 }
 
 /************************************************************************
@@ -153,12 +156,20 @@ void
 btr_search_disable(void)
 /*====================*/
 {
-	btr_search_disabled = TRUE;
+	mutex_enter(&btr_search_enabled_mutex);
 	rw_lock_x_lock(&btr_search_latch);
 
-	ha_clear(btr_search_sys->hash_index);
+	btr_search_enabled = FALSE;
+
+	/* Clear all block->is_hashed flags and remove all entries
+	from btr_search_sys->hash_index. */
+	buf_pool_drop_hash_index();
+
+	/* btr_search_enabled_mutex should guarantee this. */
+	ut_ad(!btr_search_enabled);
 
 	rw_lock_x_unlock(&btr_search_latch);
+	mutex_exit(&btr_search_enabled_mutex);
 }
 
 /************************************************************************
@@ -168,7 +179,13 @@ void
 btr_search_enable(void)
 /*====================*/
 {
-	btr_search_disabled = FALSE;
+	mutex_enter(&btr_search_enabled_mutex);
+	rw_lock_x_lock(&btr_search_latch);
+
+	btr_search_enabled = TRUE;
+
+	rw_lock_x_unlock(&btr_search_latch);
+	mutex_exit(&btr_search_enabled_mutex);
 }
 
 /*********************************************************************
@@ -797,6 +814,10 @@ btr_search_guess_on_hash(
 
 	if (UNIV_LIKELY(!has_search_latch)) {
 		rw_lock_s_lock(&btr_search_latch);
+
+		if (UNIV_UNLIKELY(!btr_search_enabled)) {
+			goto failure_unlock;
+		}
 	}
 
 	ut_ad(btr_search_latch.writer != RW_LOCK_EX);
@@ -1301,6 +1322,10 @@ btr_search_build_page_hash_index(
 
 	rw_lock_x_lock(&btr_search_latch);
 
+	if (UNIV_UNLIKELY(!btr_search_enabled)) {
+		goto exit_func;
+	}
+
 	if (block->is_hashed && ((block->curr_n_fields != n_fields)
 				 || (block->curr_n_bytes != n_bytes)
 				 || (block->curr_left_side != left_side))) {

buf/buf0buf.c

@@ -998,6 +998,88 @@ buf_pool_free(void)
 	buf_pool->n_chunks = 0;
 }
 
+
+/************************************************************************
+Drops the adaptive hash index.  To prevent a livelock, this function
+is only to be called while holding btr_search_latch and while
+btr_search_enabled == FALSE. */
+UNIV_INTERN
+void
+buf_pool_drop_hash_index(void)
+/*==========================*/
+{
+	ibool		released_search_latch;
+
+#ifdef UNIV_SYNC_DEBUG
+	ut_ad(rw_lock_own(&btr_search_latch, RW_LOCK_EX));
+#endif /* UNIV_SYNC_DEBUG */
+	ut_ad(!btr_search_enabled);
+
+	do {
+		buf_chunk_t*	chunks	= buf_pool->chunks;;
+		buf_chunk_t*	chunk	= chunks + buf_pool->n_chunks;
+
+		released_search_latch = FALSE;
+
+		while (--chunk >= chunks) {
+			buf_block_t*	block	= chunk->blocks;
+			ulint		i	= chunk->size;
+
+			for (; i--; block++) {
+				/* block->is_hashed cannot be modified
+				when we have an x-latch on btr_search_latch;
+				see the comment in buf0buf.h */
+
+				if (!block->is_hashed) {
+					continue;
+				}
+
+				/* To follow the latching order, we
+				have to release btr_search_latch
+				before acquiring block->latch. */
+				rw_lock_x_unlock(&btr_search_latch);
+				/* When we release the search latch,
+				we must rescan all blocks, because
+				some may become hashed again. */
+				released_search_latch = TRUE;
+
+				rw_lock_x_lock(&block->lock);
+
+				/* This should be guaranteed by the
+				callers, which will be holding
+				btr_search_enabled_mutex. */
+				ut_ad(!btr_search_enabled);
+
+				/* Because we did not buffer-fix the
+				block by calling buf_block_get_gen(),
+				it is possible that the block has been
+				allocated for some other use after
+				btr_search_latch was released above.
+				We do not care which file page the
+				block is mapped to.  All we want to do
+				is to drop any hash entries referring
+				to the page. */
+
+				/* It is possible that
+				block->page.state != BUF_FILE_PAGE.
+				Even that does not matter, because
+				btr_search_drop_page_hash_index() will
+				check block->is_hashed before doing
+				anything.  block->is_hashed can only
+				be set on uncompressed file pages. */
+
+				btr_search_drop_page_hash_index(block);
+
+				rw_lock_x_unlock(&block->lock);
+
+				rw_lock_x_lock(&btr_search_latch);
+
+				ut_ad(!btr_search_enabled);
+			}
+		}
+	} while (released_search_latch);
+}
+
 /************************************************************************
 Relocate a buffer control block.  Relocates the block on the LRU list
 and in buf_pool->page_hash.  Does not relocate bpage->list.

handler/ha_innodb.cc

@@ -167,7 +167,6 @@ static my_bool	innobase_locks_unsafe_for_binlog	= FALSE;
 static my_bool	innobase_rollback_on_timeout		= FALSE;
 static my_bool	innobase_create_status_file		= FALSE;
 static my_bool	innobase_stats_on_metadata		= TRUE;
-static my_bool	innobase_adaptive_hash_index		= TRUE;
 
 static char*	internal_innobase_data_file_path	= NULL;
 
@@ -2117,8 +2116,6 @@ innobase_init(
 	srv_max_n_open_files = (ulint) innobase_open_files;
 	srv_innodb_status = (ibool) innobase_create_status_file;
 
-	btr_search_disabled = (ibool) !innobase_adaptive_hash_index;
-
 	srv_print_verbose_log = mysqld_embedded ? 0 : 1;
 
 	/* Store the default charset-collation number of this MySQL
@@ -9362,6 +9359,28 @@ innodb_file_format_check_update(
 	}
 }
 
+/********************************************************************
+Update the system variable innodb_adaptive_hash_index using the "saved"
+value. This function is registered as a callback with MySQL. */
+static
+void
+innodb_adaptive_hash_index_update(
+/*==============================*/
+	THD*				thd,		/* in: thread handle */
+	struct st_mysql_sys_var*	var,		/* in: pointer to
+							system variable */
+	void*				var_ptr,	/* out: where the
+							formal string goes */
+	const void*			save)		/* in: immediate result
+							from check function */
+{
+	if (*(my_bool*) save) {
+		btr_search_enable();
+	} else {
+		btr_search_disable();
+	}
+}
+
 /*****************************************************************
 Check if it is a valid value of innodb_change_buffering.  This function is
 registered as a callback with MySQL. */
@@ -9552,11 +9571,11 @@ static MYSQL_SYSVAR_ULONGLONG(stats_sample_pages, srv_stats_sample_pages,
   "The number of index pages to sample when calculating statistics (default 8)",
   NULL, NULL, 8, 1, ~0ULL, 0);
 
-static MYSQL_SYSVAR_BOOL(adaptive_hash_index, innobase_adaptive_hash_index,
-  PLUGIN_VAR_OPCMDARG | PLUGIN_VAR_READONLY,
+static MYSQL_SYSVAR_BOOL(adaptive_hash_index, btr_search_enabled,
+  PLUGIN_VAR_OPCMDARG,
   "Enable InnoDB adaptive hash index (enabled by default).  "
   "Disable with --skip-innodb-adaptive-hash-index.",
-  NULL, NULL, TRUE);
+  NULL, innodb_adaptive_hash_index_update, TRUE);
 
 static MYSQL_SYSVAR_ULONG(replication_delay, srv_replication_delay,
   PLUGIN_VAR_RQCMDARG,

include/btr0sea.h

@@ -165,8 +165,9 @@ btr_search_validate(void);
 /*======================*/
 				/* out: TRUE if ok */
 
-/* Flag: has the search system been disabled? */
-extern ibool btr_search_disabled;
+/* Flag: has the search system been enabled?
+Protected by btr_search_latch and btr_search_enabled_mutex. */
+extern char btr_search_enabled;
 
 /* The search info struct in an index */
 

include/buf0buf.h

@@ -92,6 +92,15 @@ void
 buf_pool_free(void);
 /*===============*/
 
+/************************************************************************
+Drops the adaptive hash index.  To prevent a livelock, this function
+is only to be called while holding btr_search_latch and while
+btr_search_enabled == FALSE. */
+UNIV_INTERN
+void
+buf_pool_drop_hash_index(void);
+/*==========================*/
+
 /************************************************************************
 Relocate a buffer control block.  Relocates the block on the LRU list
 and in buf_pool->page_hash.  Does not relocate bpage->list.

include/sync0sync.h

@@ -433,7 +433,8 @@ or row lock! */
 #define SYNC_TRX_SYS_HEADER	290
 #define SYNC_LOG		170
 #define SYNC_RECV		168
-#define SYNC_WORK_QUEUE		161
+#define	SYNC_WORK_QUEUE		162
+#define	SYNC_SEARCH_SYS_CONF	161	/* for assigning btr_search_enabled */
 #define	SYNC_SEARCH_SYS		160	/* NOTE that if we have a memory
 					heap that can be extended to the
 					buffer pool, its logical level is

sync/sync0sync.c

@@ -1059,6 +1059,7 @@ sync_thread_add_level(
 	case SYNC_DOUBLEWRITE:
 	case SYNC_BUF_POOL:
 	case SYNC_SEARCH_SYS:
+	case SYNC_SEARCH_SYS_CONF:
 	case SYNC_TRX_LOCK_HEAP:
 	case SYNC_KERNEL:
 	case SYNC_IBUF_BITMAP_MUTEX: