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# name : bug677407
# introduced : 13
# maintainer : Alexey
LP bug#677407 / MySQL Bug#48883: Stale data from INNODB_LOCKS table.
The innodb.innodb_information_schema test could fail sporadically due to
the flawed logic in the INFORMATION_SCHEMA.INNODB_LOCKS caching
mechanism.
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).
Fixed 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 -ruN a/storage/innodb_plugin/trx/trx0i_s.c b/storage/innodb_plugin/trx/trx0i_s.c
--- a/storage/innodb_plugin/trx/trx0i_s.c 2010-11-03 16:39:54.000000000 +0300
+++ b/storage/innodb_plugin/trx/trx0i_s.c 2010-11-30 13:57:03.000000000 +0300
@@ -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 */
@@ -1142,13 +1138,6 @@
{
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
@@ -1246,6 +1235,12 @@
/*===================================*/
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);
@@ -1258,6 +1253,10 @@
mutex_exit(&kernel_mutex);
+ /* update cache last read time */
+ now = ut_time_us(NULL);
+ cache->last_read = now;
+
return(0);
}
@@ -1288,16 +1287,12 @@
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,
@@ -1348,18 +1343,10 @@
/*===================*/
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);
}
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