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IN QUERY CACHE CODE DESCRIPTION: MySQL Server crashes sporadically when Query Caching is on and the server has high contention among clients. ANALYSIS : Scenario 1: In Query_cache::move_by_type() when handling RESULT or its related blocks, Write Lock is acquired on its parent Query block. However the next and prev pointers are cached in local variables before lock acquisition. In an extremely high contention scenario there exists a possibility that Query_cache::append_result_data() is operating on the same query block and as a consequence might append a new Result block to the end of Result blocks Linked List of the Query. This would manipulate the next, prev pointers of the Block being processed in move_by_type(), however the local pointers still point to previous nodes there by causing Data Corruption leading to crash. Scenario 2: In Windows SDK "BOOL" is typedefed as "int" and BOOLEAN is typedefed as "usigned char". The function pointer definition "srw_bool_func" mistakenly uses BOOL instead of BOOLEAN thereby virtually making the function my_TryAcquireSRWLockExclusive() always succeed because only the LSB of EAX has the actual result of the call, however due to type mismatch all bytes of EAX are used for evaluation. Again during high contention scenarios in Query_cache::free_old_query() calls try_lock_writing() on a Query, this call always succeeds and the query is freed, even though it is used by some other thread, in this case Query_cache::send_result_to_client() was using it and the code causes a crash because it accessed free or reallocated memory. FIX : Scenario 1: The next, prev pointers are now accessed only after Lock acquisition in Query_cache::move_by_type(). Scenario 2: In the definition of "srw_bool_func" BOOL has been replaced with "BOOLEAN"
MySQL Server 5.5 This is a release of MySQL, a dual-license SQL database server. For the avoidance of doubt, this particular copy of the software is released under the version 2 of the GNU General Public License. MySQL is brought to you by Oracle. Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved. License information can be found in the COPYING file. MySQL FOSS License Exception We want free and open source software applications under certain licenses to be able to use specified GPL-licensed MySQL client libraries despite the fact that not all such FOSS licenses are compatible with version 2 of the GNU General Public License. Therefore there are special exceptions to the terms and conditions of the GPLv2 as applied to these client libraries, which are identified and described in more detail in the FOSS License Exception at <http://www.mysql.com/about/legal/licensing/foss-exception.html>. This distribution may include materials developed by third parties. For license and attribution notices for these materials, please refer to the documentation that accompanies this distribution (see the "Licenses for Third-Party Components" appendix) or view the online documentation at <http://dev.mysql.com/doc/>. GPLv2 Disclaimer For the avoidance of doubt, except that if any license choice other than GPL or LGPL is available it will apply instead, Oracle elects to use only the General Public License version 2 (GPLv2) at this time for any software where a choice of GPL license versions is made available with the language indicating that GPLv2 or any later version may be used, or where a choice of which version of the GPL is applied is otherwise unspecified. For further information about MySQL or additional documentation, see: - The latest information about MySQL: http://www.mysql.com - The current MySQL documentation: http://dev.mysql.com/doc Some Reference Manual sections of special interest: - If you are migrating from an older version of MySQL, please read the "Upgrading from..." section. - To see what MySQL can do, take a look at the features section. - For installation instructions, see the Installing and Upgrading chapter. - For the new features/bugfix history, see the MySQL Change History appendix. You can browse the MySQL Reference Manual online or download it in any of several formats at the URL given earlier in this file. Source distributions include a local copy of the manual in the Docs directory.