------------------------------------------------------------
revno: 2977
committer: knielsen@knielsen-hq.org
branch nick: mariadb-5.1
timestamp: Fri 2010-11-19 12:17:57 +0100
message:
  Mbug#677407 / MySQL Bug#48883: Stale data from INNODB_LOCKS table.
  
  The logic for how to check when to update the table cache for
  INNODB_LOCKS with real data was flawed. This could result in both
  not updating the cache often enough (when the table is queried
  repeatedly with less than 100 milliseconds in-between) resulting
  in stale data; as well as updating too often (when multiple
  queries against the table start at around the same time).
  
  This caused occasional test failures in innodb_information_schema.
  
  Fix by updating the "last updated" timestamp in the right place,
  when the cache is updated, not when it is read.

  I hereby grant Percona the following BSD license to this patch
  for inclusion in Percona Server:

  Copyright (c) 2010, Kristian Nielsen
  All rights reserved.

  Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

      * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
      * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
      * Neither the name of the author nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff:
=== modified file 'storage/innodb_plugin/trx/trx0i_s.c'
--- storage/innodb_plugin/trx/trx0i_s.c	2010-05-14 13:08:15 +0000
+++ storage/innodb_plugin/trx/trx0i_s.c	2010-11-19 11:17:57 +0000
@@ -157,10 +157,6 @@
 	ullint		last_read;	/*!< last time the cache was read;
 					measured in microseconds since
 					epoch */
-	mutex_t		last_read_mutex;/*!< mutex protecting the
-					last_read member - it is updated
-					inside a shared lock of the
-					rw_lock member */
 	i_s_table_cache_t innodb_trx;	/*!< innodb_trx table */
 	i_s_table_cache_t innodb_locks;	/*!< innodb_locks table */
 	i_s_table_cache_t innodb_lock_waits;/*!< innodb_lock_waits table */
@@ -1101,13 +1097,6 @@
 {
 	ullint	now;
 
-	/* Here we read cache->last_read without acquiring its mutex
-	because last_read is only updated when a shared rw lock on the
-	whole cache is being held (see trx_i_s_cache_end_read()) and
-	we are currently holding an exclusive rw lock on the cache.
-	So it is not possible for last_read to be updated while we are
-	reading it. */
-
 #ifdef UNIV_SYNC_DEBUG
 	ut_a(rw_lock_own(&cache->rw_lock, RW_LOCK_EX));
 #endif
@@ -1205,6 +1194,12 @@
 /*===================================*/
 	trx_i_s_cache_t*	cache)	/*!< in/out: cache */
 {
+	ullint	now;
+
+#ifdef UNIV_SYNC_DEBUG
+	ut_a(rw_lock_own(&cache->rw_lock, RW_LOCK_EX));
+#endif
+
 	if (!can_cache_be_updated(cache)) {
 
 		return(1);
@@ -1217,6 +1212,10 @@
 
 	mutex_exit(&kernel_mutex);
 
+	/* update cache last read time */
+	now = ut_time_us(NULL);
+	cache->last_read = now;
+
 	return(0);
 }
 
@@ -1247,16 +1246,12 @@
 	release kernel_mutex
 	release trx_i_s_cache_t::rw_lock
 	acquire trx_i_s_cache_t::rw_lock, S
-	acquire trx_i_s_cache_t::last_read_mutex
-	release trx_i_s_cache_t::last_read_mutex
 	release trx_i_s_cache_t::rw_lock */
 
 	rw_lock_create(&cache->rw_lock, SYNC_TRX_I_S_RWLOCK);
 
 	cache->last_read = 0;
 
-	mutex_create(&cache->last_read_mutex, SYNC_TRX_I_S_LAST_READ);
-
 	table_cache_init(&cache->innodb_trx, sizeof(i_s_trx_row_t));
 	table_cache_init(&cache->innodb_locks, sizeof(i_s_locks_row_t));
 	table_cache_init(&cache->innodb_lock_waits,
@@ -1307,18 +1302,10 @@
 /*===================*/
 	trx_i_s_cache_t*	cache)	/*!< in: cache */
 {
-	ullint	now;
-
 #ifdef UNIV_SYNC_DEBUG
 	ut_a(rw_lock_own(&cache->rw_lock, RW_LOCK_SHARED));
 #endif
 
-	/* update cache last read time */
-	now = ut_time_us(NULL);
-	mutex_enter(&cache->last_read_mutex);
-	cache->last_read = now;
-	mutex_exit(&cache->last_read_mutex);
-
 	rw_lock_s_unlock(&cache->rw_lock);
 }