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Since ce0fdbfe9722, a replication slot and an origin are created by each tablesync worker, whose information is stored in both a catalog and shared memory (once the origin is set up in the latter case). The transaction where the origin is created is the same as the one that runs the initial COPY, with the catalog state of the origin becoming visible for other sessions only once the COPY transaction has committed. The catalog state is coupled with a state in shared memory, initialized at the same time as the origin created in the catalogs. Note that the transaction doing the initial data sync can take a long time, time that depends on the amount of data to transfer from a publication node to its subscriber node. Now, when a DROP SUBSCRIPTION is executed, all its workers are stopped with the origins removed. The removal of each origin relies on a catalog lookup. A worker still running the initial COPY would fail its transaction, with the catalog state of the origin rolled back while the shared memory state remains around. The session running the DROP SUBSCRIPTION should be in charge of cleaning up the catalog and the shared memory state, but as there is no data in the catalogs the shared memory state is not removed. This issue would leave orphaned origin data in shared memory, leading to a confusing state as it would still show up in pg_replication_origin_status. Note that this shared memory data is sticky, being flushed on disk in replorigin_checkpoint at checkpoint. This prevents other origins from reusing a slot position in the shared memory data. To address this problem, the commit moves the creation of the origin at the end of the transaction that precedes the one executing the initial COPY, making the origin immediately visible in the catalogs for other sessions, giving DROP SUBSCRIPTION a way to know about it. A different solution would have been to clean up the shared memory state using an abort callback within the tablesync worker. The solution of this commit is more consistent with the apply worker that creates an origin in a short transaction. A test is added in the subscription test 004_sync.pl, which was able to display the problem. The test fails when this commit is reverted. Reported-by: Tenglong Gu <brucegu@amazon.com> Reported-by: Daisuke Higuchi <higudai@amazon.com> Analyzed-by: Michael Paquier <michael@paquier.xyz> Author: Hou Zhijie <houzj.fnst@fujitsu.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com> Discussion: https://postgr.es/m/aUTekQTg4OYnw-Co@paquier.xyz Backpatch-through: 14
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. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download/ See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.