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We've long had a policy that any toasted fields in a catalog tuple should be pulled in-line before entering the tuple in a catalog cache. However, that requires access to the catalog's toast table, and we'll typically do AcceptInvalidationMessages while opening the toast table. So it's possible that the catalog tuple is outdated by the time we finish detoasting it. Since no cache entry exists yet, we can't mark the entry stale during AcceptInvalidationMessages, and instead we'll press forward and build an apparently-valid cache entry. The upshot is that we have a race condition whereby an out-of-date entry could be made in a backend's catalog cache, and persist there indefinitely causing indeterminate misbehavior. To fix, use the existing systable_recheck_tuple code to recheck whether the catalog tuple is still up-to-date after we finish detoasting it. If not, loop around and restart the process of searching the catalog and constructing cache entries from the top. The case is rare enough that this shouldn't create any meaningful performance penalty, even in the SearchCatCacheList case where we need to tear down and reconstruct the whole list. Indeed, the case is so rare that AFAICT it doesn't occur during our regression tests, and there doesn't seem to be any easy way to build a test that would exercise it reliably. To allow testing of the retry code paths, add logic (in USE_ASSERT_CHECKING builds only) that randomly pretends that the recheck failed about one time out of a thousand. This is enough to ensure that we'll pass through the retry paths during most regression test runs. By adding an extra level of looping, this commit creates a need to reindent most of SearchCatCacheMiss and SearchCatCacheList. I'll do that separately, to allow putting those changes in .git-blame-ignore-revs. Patch by me; thanks to Alexander Lakhin for having built a test case to prove the bug is real, and to Xiaoran Wang for review. Back-patch to all supported branches. Discussion: https://postgr.es/m/1393953.1698353013@sss.pgh.pa.us Discussion: https://postgr.es/m/CAGjhLkOoBEC9mLsnB42d3CO1vcMx71MLSEuigeABbQ8oRdA6gw@mail.gmail.com |
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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. Copyright and license information can be found in the file COPYRIGHT. General documentation about this version of PostgreSQL can be found at: https://www.postgresql.org/docs/devel/ In particular, information about building PostgreSQL from the source code can be found at: https://www.postgresql.org/docs/devel/installation.html The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.