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
Branch
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REL_12_STABLE
Details
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https://git.postgresql.org/pg/commitdiff/139c439730b1444be88203cf867e60dd7533b294
Modified Files
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doc/src/sgml/config.sgml | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)