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b0229f26da
Commit 857f9c36cda (which taught nbtree VACUUM to skip a scan of the index from btcleanup in situations where it doesn't seem worth it) made VACUUM maintain the oldest btpo.xact among all deleted pages for the index as a whole. It failed to handle all the details surrounding pages that are deleted by the current VACUUM operation correctly (though pages deleted by some previous VACUUM operation were processed correctly). The most immediate problem was that the special area of the page was examined without a buffer pin at one point. More fundamentally, the handling failed to account for the full range of _bt_pagedel() behaviors. For example, _bt_pagedel() sometimes deletes internal pages in passing, as part of deleting an entire subtree with btvacuumpage() caller's page as the leaf level page. The original leaf page passed to _bt_pagedel() might not be the page that it deletes first in cases where deletion can take place. It's unclear how disruptive this bug may have been, or what symptoms users might want to look out for. The issue was spotted during unrelated code review. To fix, push down the logic for maintaining the oldest btpo.xact to _bt_pagedel(). btvacuumpage() is now responsible for pages that were fully deleted by a previous VACUUM operation, while _bt_pagedel() is now responsible for pages that were deleted by the current VACUUM operation (this includes half-dead pages from a previous interrupted VACUUM operation that become fully deleted in _bt_pagedel()). Note that _bt_pagedel() should never encounter an existing deleted page. This commit theoretically breaks the ABI of a stable release by changing the signature of _bt_pagedel(). However, if any third party extension is actually affected by this, then it must already be completely broken (since there are numerous assumptions made in _bt_pagedel() that cannot be met outside of VACUUM). It seems highly unlikely that such an extension actually exists, in any case. Author: Peter Geoghegan Reviewed-By: Masahiko Sawada Discussion: https://postgr.es/m/CAH2-WzkrXBcMQWAYUJMFTTvzx_r4q=pYSjDe07JnUXhe+OZnJA@mail.gmail.com Backpatch: 11-, where the "skip full scan" feature was introduced.
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download/ See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.