f731cfa94c
A review of the code has showed up a couple of issues fixed by this commit: - Physical slots have been using the confirmed LSN position as a start comparison point which is always 0/0, instead use the restart LSN position (logical slots need to use the confirmed LSN position, which was correct). - The actual slot update was incorrect for both physical and logical slots. Physical slots need to use their restart_lsn as base comparison point (confirmed_flush was used because of previous point), and logical slots need to begin reading WAL from restart_lsn (confirmed_flush was used as well), while confirmed_flush is compiled depending on the decoding context and record read, and is the LSN position returned back to the caller. - Never return 0/0 if a slot cannot be advanced. This way, if a slot is advanced while the activity is idle, then the same position is returned to the caller over and over without raising an error. Instead return the LSN the slot has been advanced to. With repetitive calls, the same position is returned hence caller can directly monitor the difference in progress in bytes by doing simply LSN difference calculations, which should be monotonic. Note that as the slot is owned by the backend advancing it, then the read of those fields is fine lock-less, while updates need to happen while the slot mutex is held, so fix that on the way as well. Other locks for in-memory data of replication slots have been already fixed previously. Some of those issues have been pointed out by Petr and Simon during the patch, while I noticed some of them after looking at the code. This also visibly takes of a recently-discovered bug causing assertion failures which can be triggered by a two-step slot forwarding which first advanced the slot to a WAL page boundary and secondly advanced it to the latest position, say 'FF/FFFFFFF' to make sure that the newest LSN is used as forward point. It would have been nice to drop a test for that, but the set of operators working on pg_lsn limits it, so this is left for a future exercise. Author: Michael Paquier Reviewed-by: Petr Jelinek, Simon Riggs Discussion: https://postgr.es/m/CANP8+jLyS=X-CAk59BJnsxKQfjwrmKicHQykyn52Qj-Q=9GLCw@mail.gmail.com Discussion: https://www.postgresql.org/message-id/2840048a-1184-417a-9da8-3299d207a1d7%40postgrespro.ru |
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README
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/.