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The XLogRecordPageWithFreeSpace function updates the freespace map (FSM) data
while replaying data-level WAL records during the recovery. If the FSM block
is updated, it needs to be marked as modified. Currently, this is done with
the MarkBufferDirtyHint call (as in all other cases for modifying FSM data).
However, in the recovery context, this function will actually do nothing if
checksums are enabled. It's assumed that the page should not be dirtied
during recovery while modifying hints to protect against torn pages, since no
new WAL data can be generated at this point to store FPI.
Such logic does not seem fully aligned with the FSM case, as its blocks could
be simply zeroed if a checksum mismatch is detected. Currently, changes to an
FSM block could be lost if each change to that block occurs infrequently
enough to allow it to be evicted from the cache. To persist the change, the
modification needs to be performed while the FSM block is still kept in
buffers and marked as dirty after receiving its FPI. If the block has already
been cleaned, the change won't be persisted, so stored FSM blocks may remain
in an obsolete state.
If a large number of discrepancies between the data in leaf FSM blocks and the
actual data blocks accumulate on the replica server, this could cause
significant delays in insert operations after switchover. Such an insert
operation may need to visit many data blocks marked as having sufficient
space in the FSM, only to discover that the information is incorrect and the
FSM records need to be corrected. In a heavily trafficked insert-only table
with many concurrent clients performing inserts, this has been observed to
cause several-second stalls, causing visible application malfunction. The
desire to avoid such cases was the reason behind the commit
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| .cirrus.star | ||
| .cirrus.tasks.yml | ||
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| .dir-locals.el | ||
| .editorconfig | ||
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| .gitattributes | ||
| .gitignore | ||
| aclocal.m4 | ||
| configure | ||
| configure.ac | ||
| COPYRIGHT | ||
| GNUmakefile.in | ||
| HISTORY | ||
| Makefile | ||
| meson.build | ||
| meson_options.txt | ||
| README | ||
| README.git | ||
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/.