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Fix cross-checking of ReservedBackends/max_wal_senders/MaxConnections.

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We were independently checking ReservedBackends < MaxConnections and
max_wal_senders < MaxConnections, but because walsenders aren't allowed
to use superuser-reserved connections, that's really the wrong thing.
Correct behavior is to insist on ReservedBackends + max_wal_senders being
less than MaxConnections.  Fix the code and associated documentation.

This has been wrong for a long time, but since the situation probably
hardly ever arises in the field (especially pre-v10, when the default
for max_wal_senders was zero), no back-patch.

Discussion: https://postgr.es/m/28271.1520195491@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2018-03-08 11:25:26 -05:00
parent f9f8784c8b
commit 4e0c743c18
4 changed files with 24 additions and 21 deletions
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15
src/backend/postmaster/postmaster.c
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@@ -202,9 +202,9 @@ char *ListenAddresses;
/*
* ReservedBackends is the number of backends reserved for superuser use.
* This number is taken out of the pool size given by MaxBackends so
* This number is taken out of the pool size given by MaxConnections so
* number of backend slots available to non-superusers is
* (MaxBackends - ReservedBackends). Note what this really means is
* (MaxConnections - ReservedBackends). Note what this really means is
* "if there are <= ReservedBackends connections available, only superusers
* can make new connections" --- pre-existing superuser connections don't
* count against the limit.
@@ -882,14 +882,11 @@ PostmasterMain(int argc, char *argv[])
/*
* Check for invalid combinations of GUC settings.
*/
if (ReservedBackends >= MaxConnections)
if (ReservedBackends + max_wal_senders >= MaxConnections)
{
write_stderr("%s: superuser_reserved_connections must be less than max_connections\n", progname);
ExitPostmaster(1);
}
if (max_wal_senders >= MaxConnections)
{
write_stderr("%s: max_wal_senders must be less than max_connections\n", progname);
write_stderr("%s: superuser_reserved_connections (%d) plus max_wal_senders (%d) must be less than max_connections (%d)\n",
progname,
ReservedBackends, max_wal_senders, MaxConnections);
ExitPostmaster(1);
}
if (XLogArchiveMode > ARCHIVE_MODE_OFF && wal_level == WAL_LEVEL_MINIMAL)