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VACUUM's wraparound failsafe mode exists to reclaim transaction IDs as quickly as possible.4830f10243made the failsafe stop using the BAS_VACUUM buffer access strategy so that the rest of the vacuum could make use of all of shared buffers rather than being confined to the small strategy ring. However, when9256822608made vacuum's first heap pass use the read stream, this was accidentally disabled. The read stream keeps its own references to the buffer access strategy, so clearing vacrel->bstrategy in lazy_check_wraparound_failsafe() no longer had any effect on the reads issued by the first pass. Fix this by adding clearing the BufferAccessStrategy reference actually being used by the ongoing scan -- those in the ReadBuffersOperations structs themselves. Two things we accept rather than fix, as neither is worth the added complexity given how rarely failsafe mode is reached: - A small amount of read time for IOs that were already in progress when the strategy was cleared may be attributed to IOCONTEXT_NORMAL instead of IOCONTEXT_VACUUM. WaitReadBuffers() derives the IOContext from the (now cleared) strategy, so the wait time of these in-flight IOs is misattributed. This is bounded by the stream's look-ahead window and happens at most once per vacuum, when the strategy is first cleared. - The stream's buffer pin limit stays lower than it would have been had no strategy been used at all. max_pinned_buffers is capped by the strategy's pin limit when the stream is created and is not recomputed when the strategy is cleared. Raising it would mean building a new, larger ring, which would require first waiting for all in-progress IOs to complete. That didn't seem worth it. Reported-by: Jingtang Zhang <mrdrivingduck@gmail.com> Discussion: https://postgr.es/m/CAPsk3_APRYVLhAJ5TMwdmpSx8W_%3DPHMm%3DPmKAvnC3gBrfNommQ%40mail.gmail.com Backpatch-to: 18
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/19/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/19/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/.