From ea92368cd1da1e290f9ab8efb7f60cb7598fc310 Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Tue, 12 Feb 2019 10:07:56 +0900 Subject: Move max_wal_senders out of max_connections for connection slot handling MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Since its introduction, max_wal_senders is counted as part of max_connections when it comes to define how many connection slots can be used for replication connections with a WAL sender context. This can lead to confusion for some users, as it could be possible to block a base backup or replication from happening because other backend sessions are already taken for other purposes by an application, and superuser-only connection slots are not a correct solution to handle that case. This commit makes max_wal_senders independent of max_connections for its handling of PGPROC entries in ProcGlobal, meaning that connection slots for WAL senders are handled using their own free queue, like autovacuum workers and bgworkers. One compatibility issue that this change creates is that a standby now requires to have a value of max_wal_senders at least equal to its primary. So, if a standby created enforces the value of max_wal_senders to be lower than that, then this could break failovers. Normally this should not be an issue though, as any settings of a standby are inherited from its primary as postgresql.conf gets normally copied as part of a base backup, so parameters would be consistent. Author: Alexander Kukushkin Reviewed-by: Kyotaro Horiguchi, Petr Jelínek, Masahiko Sawada, Oleksii Kliukin Discussion: https://postgr.es/m/CAFh8B=nBzHQeYAu0b8fjK-AF1X4+_p6GRtwG+cCgs6Vci2uRuQ@mail.gmail.com --- src/backend/access/transam/xlog.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'src/backend/access/transam/xlog.c') diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index a9f32728495..ecd12fc53ae 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -5257,6 +5257,7 @@ BootStrapXLOG(void) /* Set important parameter values for use when replaying WAL */ ControlFile->MaxConnections = MaxConnections; ControlFile->max_worker_processes = max_worker_processes; + ControlFile->max_wal_senders = max_wal_senders; ControlFile->max_prepared_xacts = max_prepared_xacts; ControlFile->max_locks_per_xact = max_locks_per_xact; ControlFile->wal_level = wal_level; @@ -6170,6 +6171,9 @@ CheckRequiredParameterValues(void) RecoveryRequiresIntParameter("max_worker_processes", max_worker_processes, ControlFile->max_worker_processes); + RecoveryRequiresIntParameter("max_wal_senders", + max_wal_senders, + ControlFile->max_wal_senders); RecoveryRequiresIntParameter("max_prepared_transactions", max_prepared_xacts, ControlFile->max_prepared_xacts); @@ -9460,6 +9464,7 @@ XLogReportParameters(void) wal_log_hints != ControlFile->wal_log_hints || MaxConnections != ControlFile->MaxConnections || max_worker_processes != ControlFile->max_worker_processes || + max_wal_senders != ControlFile->max_wal_senders || max_prepared_xacts != ControlFile->max_prepared_xacts || max_locks_per_xact != ControlFile->max_locks_per_xact || track_commit_timestamp != ControlFile->track_commit_timestamp) @@ -9478,6 +9483,7 @@ XLogReportParameters(void) xlrec.MaxConnections = MaxConnections; xlrec.max_worker_processes = max_worker_processes; + xlrec.max_wal_senders = max_wal_senders; xlrec.max_prepared_xacts = max_prepared_xacts; xlrec.max_locks_per_xact = max_locks_per_xact; xlrec.wal_level = wal_level; @@ -9493,6 +9499,7 @@ XLogReportParameters(void) ControlFile->MaxConnections = MaxConnections; ControlFile->max_worker_processes = max_worker_processes; + ControlFile->max_wal_senders = max_wal_senders; ControlFile->max_prepared_xacts = max_prepared_xacts; ControlFile->max_locks_per_xact = max_locks_per_xact; ControlFile->wal_level = wal_level; @@ -9896,6 +9903,7 @@ xlog_redo(XLogReaderState *record) LWLockAcquire(ControlFileLock, LW_EXCLUSIVE); ControlFile->MaxConnections = xlrec.MaxConnections; ControlFile->max_worker_processes = xlrec.max_worker_processes; + ControlFile->max_wal_senders = xlrec.max_wal_senders; ControlFile->max_prepared_xacts = xlrec.max_prepared_xacts; ControlFile->max_locks_per_xact = xlrec.max_locks_per_xact; ControlFile->wal_level = xlrec.wal_level; @@ -9927,7 +9935,7 @@ xlog_redo(XLogReaderState *record) UpdateControlFile(); LWLockRelease(ControlFileLock); - /* Check to see if any changes to max_connections give problems */ + /* Check to see if any parameter change gives a problem on recovery */ CheckRequiredParameterValues(); } else if (info == XLOG_FPW_CHANGE) -- cgit v1.2.3