pgsql: Invalidate inactive replication slots. - Mailing list pgsql-committers

Invalidate inactive replication slots.

This commit introduces idle_replication_slot_timeout GUC that allows
inactive slots to be invalidated at the time of checkpoint. Because
checkpoints happen checkpoint_timeout intervals, there can be some lag
between when the idle_replication_slot_timeout was exceeded and when the
slot invalidation is triggered at the next checkpoint. To avoid such lags,
users can force a checkpoint to promptly invalidate inactive slots.

Note that the idle timeout invalidation mechanism is not applicable for
slots that do not reserve WAL or for slots on the standby server that are
synced from the primary server (i.e., standby slots having 'synced' field
'true'). Synced slots are always considered to be inactive because they
don't perform logical decoding to produce changes.

The slots can become inactive for a long period if a subscriber is down
due to a system error or inaccessible because of network issues. If such a
situation persists, it might be more practical to recreate the subscriber
rather than attempt to recover the node and wait for it to catch up which
could be time-consuming.

Then, external tools could create replication slots (e.g., for migrations
or upgrades) that may fail to remove them if an error occurs, leaving
behind unused slots that take up space and resources. Manually cleaning
them up can be tedious and error-prone, and without intervention, these
lingering slots can cause unnecessary WAL retention and system bloat.

As the duration of idle_replication_slot_timeout is in minutes, any test
using that would be time-consuming. We are planning to commit a follow up
patch for tests by using the injection point framework.

Author: Nisha Moond <nisha.moond412@gmail.com>
Author: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Reviewed-by: Peter Smith <smithpb2250@gmail.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Reviewed-by: Vignesh C <vignesh21@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Hou Zhijie <houzj.fnst@fujitsu.com>
Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Discussion: https://postgr.es/m/CALj2ACW4aUe-_uFQOjdWCEN-xXoLGhmvRFnL8SNw_TZ5nJe+aw@mail.gmail.com
Discussion: https://postgr.es/m/OS0PR01MB5716C131A7D80DAE8CB9E88794FC2@OS0PR01MB5716.jpnprd01.prod.outlook.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ac0e33136abc4668c9b08e1ba7db69afe1e0e2c3

Modified Files
--------------
doc/src/sgml/config.sgml                      |  40 ++++
doc/src/sgml/logical-replication.sgml         |   5 +
doc/src/sgml/system-views.sgml                |   7 +
src/backend/access/transam/xlog.c             |   4 +-
src/backend/replication/slot.c                | 325 ++++++++++++++++++++------
src/backend/replication/slotfuncs.c           |   2 +-
src/backend/utils/adt/timestamp.c             |  18 ++
src/backend/utils/misc/guc_tables.c           |  12 +
src/backend/utils/misc/postgresql.conf.sample |   1 +
src/bin/pg_basebackup/pg_createsubscriber.c   |   4 +
src/bin/pg_upgrade/server.c                   |   7 +
src/include/replication/slot.h                |  22 +-
src/include/utils/guc_hooks.h                 |   2 +
src/include/utils/timestamp.h                 |   3 +
src/tools/pgindent/typedefs.list              |   1 +
15 files changed, 367 insertions(+), 86 deletions(-)