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When promoting a standby just after a XLOG_SWITCH record was replayed, and next segment(s) are already are locally available (via walsender, restore_command + trigger/recovery target), that segment could accidentally be recycled onto the past of the new timeline. Later checkpointer would create a .ready file for it, assuming there was an error during creation, and it would get archived. That causes trouble if another standby is later brought up from a basebackup from before the timeline creation, because it would try to read the segment, because XLogFileReadAnyTLI just tries all possible timelines, which doesn't have valid contents. Thus replay would fail. The problem, if already occurred, can be fixed by removing the segment and/or having restore_command filter it out. The reason for the creation of such "phantom" segments was, that after an XLOG_SWITCH record the EndOfLog variable points to the beginning of the next segment, and RemoveXlogFile() used XLByteToPrevSeg(). Normally RemoveXlogFile() doing so is harmless, because the last segment will still exist preventing InstallXLogFileSegment() from causing harm, but just after promotion there's no previous segment on the new timeline. Fix that by using XLByteToSeg() instead of XLByteToPrevSeg(). Author: Andres Freund Reported-By: Greg Burek Discussion: https://postgr.es/m/20170619073026.zcwpe6mydsaz5ygd@alap3.anarazel.de Backpatch: 9.2-, bug older than all supported versions
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/.