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| author | Bruce Momjian <bruce@momjian.us> | 2020-11-16 13:13:43 -0500 |
|---|---|---|
| committer | Bruce Momjian <bruce@momjian.us> | 2020-11-16 13:13:43 -0500 |
| commit | bea246117b402e59340c9efa0bdbdbe7c1ea8554 (patch) | |
| tree | 4fb5ede6f48ad4d437ec2bee9d93bf7ecbbb351d | |
| parent | 524712ceae3b443e19b54ad877d26558af7ee3d0 (diff) | |
| download | postgresql-bea246117b402e59340c9efa0bdbdbe7c1ea8554.tar.gz postgresql-bea246117b402e59340c9efa0bdbdbe7c1ea8554.zip | |
doc: update bgwriter description
This clarifies exactly what the bgwriter does, which should help with
tuning.
Reported-by: Chris Wilson
Discussion: https://postgr.es/m/160399562040.7809.7335281028960123489@wrigleys.postgresql.org
Backpatch-through: 9.5
| -rw-r--r-- | doc/src/sgml/config.sgml | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 48b2a412b63..3570b422be8 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -1909,8 +1909,11 @@ include_dir 'conf.d' There is a separate server process called the <firstterm>background writer</firstterm>, whose function is to issue writes of <quote>dirty</quote> (new or modified) shared - buffers. It writes shared buffers so server processes handling - user queries seldom or never need to wait for a write to occur. + buffers. When the number of clean shared buffers appears to be + insufficient, the background writer writes some dirty buffers to the + file system and marks them as clean. This reduces the likelihood + that server processes handling user queries will be unable to find + clean buffers and have to write dirty buffers themselves. However, the background writer does cause a net overall increase in I/O load, because while a repeatedly-dirtied page might otherwise be written only once per checkpoint interval, the |