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------------------------------------------------------------ revno: 2617.68.7 committer: Dmitry Lenev <dlenev@mysql.com> branch nick: mysql-next-bg46044 timestamp: Thu 2009-08-27 10:22:17 +0400 message: Fix for bug #46044 "MDL deadlock on LOCK TABLE + CREATE TABLE HIGH_PRIORITY FOR UPDATE". Deadlock occured when during execution of query to I_S we tried to open a table or its .FRM in order to get information about it and had to wait because we have encountered exclusive metadata lock on this table held by a DDL operation from another connection which in its turn waited for some resource currently owned by connection executing this I_S query. For example, this might have happened if one under LOCK TABLES executed I_S query targeted to particular table (which was not among locked) and also concurrently tried to create this table using CREATE TABLE SELECT which had to wait for one of tables locked by the first connection. Another situation in which deadlock might have occured is when I_S query, which was executed as part of transaction, tried to get information about table which just has been dropped by concurrent DROP TABLES executed under LOCK TABLES and this DROP TABLES for its completion also had to wait transaction from the first connection. This problem stemmed from the fact that opening of tables/.FRMs for I_S filling is happening outside of connection's main MDL_context so code which tries to detect deadlocks due to conflicting metadata locks doesn't work in this case. Indeed, this led to deadlocks when during I_S filling we tried to wait for conflicting metadata lock to go away, while its owner was waiting for some resource held by connection executing I_S query. This patch solves this problem by avoiding waiting in such situation. Instead we skip this table and produce warning that information about it was omitted from I_S due to concurrent DDL operation. We still wait for conflicting metadata lock to go away when it is known that deadlock is not possible (i.e. when connection executing I_S query does not hold any metadata or table-level locks). Basically, we apply our standard deadlock avoidance technique for metadata locks to the process of filling of I_S tables but replace ER_LOCK_DEADLOCK error with a warning. Note that this change is supposed to be safe for 'mysqldump' since the only its mode which is affected by this change is --single-transaction mode is not safe in the presence of concurrent DDL anyway (and this fact is documented). Other modes are unaffected because they either use SHOW TABLES/SELECT * FROM I_S.TABLE_NAMES which do not take any metadata locks in the process of I_S table filling and thus cannot skip tables or execute I_S queries for tables which were previously locked by LOCK TABLES (or in the presence of global read lock) which excludes possibility of encountering conflicting metadata lock. mysql-test/r/mdl_sync.result: Added test for bug #46044 "MDL deadlock on LOCK TABLE + CREATE TABLE HIGH_PRIORITY FOR UPDATE". mysql-test/t/mdl_sync.test: Added test for bug #46044 "MDL deadlock on LOCK TABLE + CREATE TABLE HIGH_PRIORITY FOR UPDATE". sql/mysql_priv.h: Added a new flag for open_table() call which allows it to fail with an error in cases when conflicting metadata lock is discovered instead of waiting until this lock goes away. sql/share/errmsg-utf8.txt: Added error/warning message to be generated in cases when information about table is omitted from I_S since there is conflicting metadata lock on the table. sql/share/errmsg.txt: Added error/warning message to be generated in cases when information about table is omitted from I_S since there is conflicting metadata lock on the table. sql/sql_base.cc: Added a new flag for open_table() call which allows it to fail with an error in cases when conflicting metadata lock is discovered instead of waiting until this lock goes away. sql/sql_show.cc: When we are opening a table (or just .FRM) in order to fill I_S with information about this table and encounter conflicting metadata lock waiting for this lock to go away can lead to a deadlock in some situations (under LOCK TABLES, within transaction, etc.). To avoid these deadlocks we detect such situations and don't do waiting. Instead, we skip table for which we have conflicting metadata lock, thus omitting information about it from I_S table, and produce an appropriate warning. |
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This directory contains a test suite for the MySQL daemon. To run the currently existing test cases, simply execute ./mysql-test-run in this directory. It will fire up the newly built mysqld and test it. Note that you do not have to have to do "make install", and you could actually have a co-existing MySQL installation. The tests will not conflict with it. All tests must pass. If one or more of them fail on your system, please read the following manual section for instructions on how to report the problem: http://dev.mysql.com/doc/mysql/en/mysql-test-suite.html If you want to use an already running MySQL server for specific tests, use the --extern option to mysql-test-run. Please note that in this mode, the test suite expects you to provide the names of the tests to run. For example, here is the command to run the "alias" and "analyze" tests with an external server: mysql-test-run --extern alias analyze To match your setup, you might also need to provide --socket, --user, and other relevant options. With no test cases named on the command line, mysql-test-run falls back to the normal "non-extern" behavior. The reason for this is that some tests cannot run with an external server. You can create your own test cases. To create a test case, create a new file in the t subdirectory using a text editor. The file should have a .test extension. For example: xemacs t/test_case_name.test In the file, put a set of SQL statements that create some tables, load test data, and run some queries to manipulate it. We would appreciate it if you name your test tables t1, t2, t3 ... (to not conflict too much with existing tables). Your test should begin by dropping the tables you are going to create and end by dropping them again. This ensures that you can run the test over and over again. If you are using mysqltest commands (like result file names) in your test case, you should create the result file as follows: mysql-test-run --record test_case_name or mysqltest --record < t/test_case_name.test If you only have a simple test cases consisting of SQL statements and comments, you can create the test case in one of the following ways: mysql-test-run --record test_case_name mysql test < t/test_case_name.test > r/test_case_name.result mysqltest --record --record-file=r/test_case_name.result < t/test_case_name.test When this is done, take a look at r/test_case_name.result - If the result is incorrect, you have found a bug. In this case, you should edit the test result to the correct results so that we can verify that the bug is corrected in future releases. To submit your test case, put your .test file and .result file(s) into a tar.gz archive, add a README that explains the problem, ftp the archive to ftp://support.mysql.com/pub/mysql/secret/ and send a mail to bugs@lists.mysql.com