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This commit introduces a new SQL function pg_sync_replication_slots() which is used to synchronize the logical replication slots from the primary server to the physical standby so that logical replication can be resumed after a failover or planned switchover. A new 'synced' flag is introduced in pg_replication_slots view, indicating whether the slot has been synchronized from the primary server. On a standby, synced slots cannot be dropped or consumed, and any attempt to perform logical decoding on them will result in an error. The logical replication slots on the primary can be synchronized to the hot standby by using the 'failover' parameter of pg-create-logical-replication-slot(), or by using the 'failover' option of CREATE SUBSCRIPTION during slot creation, and then calling pg_sync_replication_slots() on standby. For the synchronization to work, it is mandatory to have a physical replication slot between the primary and the standby aka 'primary_slot_name' should be configured on the standby, and 'hot_standby_feedback' must be enabled on the standby. It is also necessary to specify a valid 'dbname' in the 'primary_conninfo'. If a logical slot is invalidated on the primary, then that slot on the standby is also invalidated. If a logical slot on the primary is valid but is invalidated on the standby, then that slot is dropped but will be recreated on the standby in the next pg_sync_replication_slots() call provided the slot still exists on the primary server. It is okay to recreate such slots as long as these are not consumable on standby (which is the case currently). This situation may occur due to the following reasons: - The 'max_slot_wal_keep_size' on the standby is insufficient to retain WAL records from the restart_lsn of the slot. - 'primary_slot_name' is temporarily reset to null and the physical slot is removed. The slot synchronization status on the standby can be monitored using the 'synced' column of pg_replication_slots view. A functionality to automatically synchronize slots by a background worker and allow logical walsenders to wait for the physical will be done in subsequent commits. Author: Hou Zhijie, Shveta Malik, Ajin Cherian based on an earlier version by Peter Eisentraut Reviewed-by: Masahiko Sawada, Bertrand Drouvot, Peter Smith, Dilip Kumar, Nisha Moond, Kuroda Hayato, Amit Kapila Discussion: https://postgr.es/m/514f6f2f-6833-4539-39f1-96cd1e011f23@enterprisedb.com |
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PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. Copyright and license information can be found in the file COPYRIGHT. General documentation about this version of PostgreSQL can be found at: https://www.postgresql.org/docs/devel/ In particular, information about building PostgreSQL from the source code can be found at: https://www.postgresql.org/docs/devel/installation.html The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.