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08059fc049
GetPageWithFreeSpace() callers assume the returned block exists in the
main fork, failing with "could not read block" errors if that doesn't
hold. Make that assumption reliable now. It hadn't been guaranteed,
due to the weak WAL and data ordering of participating components. Most
operations on the fsm fork are not WAL-logged. Relation extension is
not WAL-logged. Hence, an fsm-fork block on disk can reference a
main-fork block that no WAL record has initialized. That could happen
after an OS crash, a replica promote, or a PITR restore. wal_log_hints
makes the trouble easier to hit; a replica promote or PITR ending just
after a relevant fsm-fork FPI_FOR_HINT may yield this broken state. The
v16 RelationAddBlocks() mechanism also makes the trouble easier to hit,
since it bulk-extends even without extension lock waiters. Commit
917dc7d239 stopped trouble around
truncation, but vectors involving PageIsNew() pages remained.
This implementation adds a RelationGetNumberOfBlocks() call when the
cached relation size doesn't confirm a block exists. We've been unable
to identify a benchmark that slows materially, but this may show up as
additional time in lseek(). An alternative without that overhead would
be a new ReadBufferMode such that ReadBufferExtended() returns NULL
after a 0-byte read, with all other errors handled normally. However,
each GetFreeIndexPage() caller would then need code for the return-NULL
case. Back-patch to v14, due to earlier versions not caching relation
size and the absence of a pre-v16 problem report.
Ronan Dunklau. Reported by Ronan Dunklau.
Discussion: https://postgr.es/m/1878547.tdWV9SEqCh%40aivenlaptop
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/.