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On restart, a replica can fail with an error like 'unexpected data beyond EOF in block 200 of relation T/D/R'. These are the steps to reproduce it: - A relation has a size of 400 blocks. - Blocks 201 to 400 are empty. - Block 200 has two rows. - Blocks 100 to 199 are empty. - A restartpoint is done - Vacuum truncates the relation to 200 blocks - A FPW deletes a row in block 200 - A checkpoint is done - A FPW deletes the last row in block 200 - Vacuum truncates the relation to 100 blocks - The replica restarts When the replica restarts: - The relation on disk starts at 100 blocks, because all the truncations were applied before restart. - The first truncate to 200 blocks is replayed. It silently fails, but it will still (incorrectly!) update the cache size to 200 blocks - The first FPW on block 200 is applied. XLogReadBufferForRead relies on the cached size and incorrectly assumes that the page already exists in the file, and thus won't extend the relation. - The online checkpoint record is replayed, calling smgrdestroyall which causes the cached size to be discarded - The second FPW on block 200 is applied. This time, the detected size is 100 blocks, an extend is attempted. However, the block 200 is already present in the buffer cache due to the first FPW. This triggers the 'unexpected data beyond EOF'. To fix, update the cached size in SmgrRelation with the current size rather than the requested new size, when the requested new size is greater. Author: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com> Discussion: https://www.postgresql.org/message-id/CAO6_Xqrv-snNJNhbj1KjQmWiWHX3nYGDgAc=vxaZP3qc4g1Siw@mail.gmail.com Backpatch-through: 14
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.
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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.
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