mirror of
https://github.com/MariaDB/server.git
synced 2026-01-06 05:22:24 +03:00
5a587b6d28
Analysis: -------- Certain queries using intrinsic temporary tables may fail due to name clashes in the file name for the temporary table when the 'temp-pool' enabled. 'temp-pool' tries to reduce the number of different filenames used for temp tables by allocating them from small pool in order to avoid problems in the Linux kernel by using a three part filename: <tmp_file_prefix>_<pid>_<temp_pool_slot_num>. The bit corresponding to the temp_pool_slot_num is set in the bit map maintained for the temp-pool when it used for the file name. It is cleared after the temp table is deleted for re-use. The 'create_tmp_table()' function call under error condition tries to clear the same bit twice by calling 'free_tmp_table()' and 'bitmap_lock_clear_bit()'. 'free_tmp_table()' does a delete of the table/file and clears the bit by calling the same function 'bitmap_lock_clear_bit()'. The issue reported can be triggered under the timing window mentioned below for an error condition while creating the temp table: a) THD1: Due to an error clears the temp pool slot number used by it by calling 'free_tmp_table'. b) THD2: In the process of creating the temp table by using an unused slot number in the bit map. c) THD1: Clears the slot number used THD2 by calling 'bitmap_lock_clear_bit()' after completing the call 'free_tmp_table'. d) THD3: Uses the slot number used the THD2 since it is freed by THD1. When it tries to create the temp file using that slot number, an error is reported since it is currently in use by THD2. [The error: Error 'Can't create/write to file '/tmp/#sql_277e_0.MYD' (Errcode: 17)'] Another issue which may occur in 5.6 and trunk is that: When the open temporary table fails after its creation(due to ulimit or OOM error), the file is not deleted. Thus further attempts to use the same slot number in the 'temp-pool' results in failure. Fix: --- a) Under the error condition calling the 'bitmap_lock_clear_bit()' function to clear the bit is unnecessary since 'free_tmp_table()' deletes the table/file and clears the bit. Hence removed the redundant call 'bitmap_lock_clear_bit()' in 'create_tmp_table()' This prevents the timing window under which the issue reported can be seen. b) If open of the temporary table fails, then the file is deleted thus allowing the temp-pool slot number to be utilized for the subsequent temporary table creation. c) Also if the attempt to create temp table fails since it already exists, the temp-pool slot for it is marked as used, to avoid the problem from re-appearing.
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 or zip archive, create a bug report at http://bugs.mysql.com/ and attach the archive to the bug report.