Lower default value of autovacuum_worker_slots in initdb as needed.
Commit c758119e5b increased the default number of semaphores
required for autovacuum workers from 3 to 16. Unfortunately, some
systems have very low default settings for SEMMNS, and this change
moved the minimum required for Postgres well beyond that limit (see
commit 38da053463 for more details).
With this commit, initdb will lower the default value for
autovacuum_worker_slots as needed, just like it already does for
parameters such as max_connections and shared_buffers. We test
for (max_connections / 6) slots, which conveniently has the
following properties:
* For the initial max_connections default of 100, the default of
autovacuum_worker_slots will be 16, which is its initial default
value specified in the documentation and in guc_tables.c.
* For the lowest possible max_connections default of 25, the
default of autovacuum_worker_slots will be 4, which means we only
need one additional semaphore for autovacuum workers (as compared
to before commit c758119e5b). This leaves some wiggle room for
new auxiliary workers, etc. on systems with low SEMMNS, and it
ensures that the default number of slots will be greater than or
equal to the default value of autovacuum_max_workers (3).
Reported-by: Tom Lane
Suggested-by: Andres Freund
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/1346002.1736198977%40sss.pgh.pa.us
Branch
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master
Details
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https://git.postgresql.org/pg/commitdiff/6d01541960e2a42c92ef67be9a1c4842cd4458d6
Modified Files
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doc/src/sgml/config.sgml | 5 +++--
src/bin/initdb/initdb.c | 40 ++++++++++++++++++++++++++++++++++------
2 files changed, 37 insertions(+), 8 deletions(-)
