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ALTER TABLE ... PARTITION BY SYSTEM_TIME with a changed INTERVAL or STARTS on a table already partitioned by SYSTEM_TIME took the fast ALTER path, which only rewrites the table definition. The history rows stayed where the old layout put them, so after the ALTER they were in wrong partitions. An unchanged interval took the copy path instead. MDEV-29873 replaced memcmp() of the intervals, which is true when they differ, with interval_t::operator==, which is true when they are equal, and lost the negation. The copy path was also broken: it assigned the whole vers_info of the new partitioning spec to the cloned partition info, now_part and hist_part included. The ALTER does not list partitions, so now_part became NULL and check_partition_info() failed with ER_VERS_WRONG_PARTS for a table with explicit partitions (MDEV-33370 test case). The fix negates the comparison again (now with interval_t::operator!=), so a changed interval rebuilds the table and redistributes the history. It copies only interval, limit and auto_hist from the new spec and keeps now_part and hist_part of the existing partitions. Without STARTS the start of the interval defaults to the current time rounded down to the INTERVAL unit. So ALTER with the same INTERVAL and no STARTS usually gets a different start and now rebuilds the table. Vers_part_info::operator=, which copied now_part and hist_part and had no other callers, is deleted. Fast ALTER was also chosen when the same statement changed the table definition, e.g. ADD COLUMN with the same INTERVAL and STARTS, or DROP COLUMN with LIMIT. It wrote the new .frm, but the partitions kept the old record layout. Now any change of the table definition (alter_info->flags) takes the copy path.
Code status:
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MariaDB: The innovative open source database
MariaDB was designed as a drop-in replacement of MySQL(R) with more features, new storage engines, fewer bugs, and better performance.
MariaDB is brought to you by the MariaDB Foundation and the MariaDB Corporation. Please read the CREDITS file for details about the MariaDB Foundation, and who is developing MariaDB.
MariaDB is developed by many of the original developers of MySQL who now work for the MariaDB Corporation, the MariaDB Foundation and by many people in the community.
MySQL, which is the base of MariaDB, is a product and trademark of Oracle Corporation, Inc. For a list of developers and other contributors, see the Credits appendix. You can also run 'SHOW authors' to get a list of active contributors.
A description of the MariaDB project and a manual can be found at:
https://mariadb.com/docs/release-notes
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Refer to the following guide: https://mariadb.org/get-involved/getting-started-for-developers/get-code-build-test/ which outlines how to build the source code correctly and run the MariaDB testing framework, as well as which branch to target for your contributions.
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