Don't rely on estimates for amcheck Bloom filters.
Solely relying on a relation's reltuples/relpages estimate to size the Bloom filters used by amcheck verification makes verification less effective when the estimates are very stale. In extreme cases, verification options that use Bloom filters internally could be totally ineffective, without users receiving any clear indication that certain types of corruption might easily be missed. To fix, use RelationGetNumberOfBlocks() instead of relpages to size the downlink block Bloom filter. Use the same RelationGetNumberOfBlocks() value to derive a minimum size for the heapallindexed Bloom filter, rather than completely trusting reltuples. Verification will still be reasonably effective when the projected/estimated number of Bloom filter elements is at least 1/5 of the final number of elements, which is assured by the new sizing logic. Reported-By: Alexander Korotkov Discussion: https://postgr.es/m/CAH2-Wzk0ke2J42KrNYBKu0Xovjy-sU5ub7PWjgpbsKdAQcL4OA@mail.gmail.com Backpatch: 11-, where downlink/heapallindexed verification were added.
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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.
PostgreSQL has many language interfaces, many of which are listed here:
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
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/.