From e6c5f1b452655a20b687b3e39d8eb816d8f8cbf7 Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Sat, 23 Oct 2021 14:43:51 +0900 Subject: [PATCH] doc: Describe calculation method of streaming start for pg_receivewal The documentation was imprecise about the starting LSN used for WAL streaming if nothing can be found in the local archive directory defined with the pg_receivewal command, so be more talkative on this matter. Extracted from a larger patch by the same author. Author: Ronan Dunklau, Michael Paquier Discussion: https://postgr.es/m/18708360.4lzOvYHigE@aivenronan Backpatch-through: 10 --- doc/src/sgml/ref/pg_receivewal.sgml | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/doc/src/sgml/ref/pg_receivewal.sgml b/doc/src/sgml/ref/pg_receivewal.sgml index 3f254f6e16..9a4a03d147 100644 --- a/doc/src/sgml/ref/pg_receivewal.sgml +++ b/doc/src/sgml/ref/pg_receivewal.sgml @@ -76,6 +76,29 @@ PostgreSQL documentation leave at least one session available for the stream. + + The starting point of the write-ahead log streaming is calculated when + pg_receivewal starts: + + + + First, scan the directory where the WAL segment files are written and + find the newest completed segment file, using as starting point the + beginning of the next WAL segment file. This is calculated independently + on the compression method used to compress each segment. + + + + + + If a starting point cannot be calculated with the previous method, + the latest WAL flush location is used as reported by the server from + a IDENTIFY_SYSTEM command. + + + + + If the connection is lost, or if it cannot be initially established, with a non-fatal error, pg_receivewal will