abf5c5c9a4
If you create a base backup using an atomic filesystem snapshot, and try to perform PITR starting from that base backup, or if you just kill a master server and create recovery.conf to put it into standby mode, we don't know how far we need to recover before reaching consistency. Normally in crash recovery, we replay all the WAL present in pg_xlog, and assume that we're consistent after that. And normally in archive recovery, minRecoveryPoint, backupEndRequired, or backupEndPoint is set in the control file, indicating how far we need to replay to reach consistency. But if the server was previously up and running normally, and you kill -9 it or take an atomic filesystem snapshot, none of those fields are set in the control file. The solution is to perform crash recovery first, replaying all the WAL in pg_xlog. After that's done, we assume that the system is consistent like in normal crash recovery, and switch to archive recovery mode after that. Per report from Kyotaro HORIGUCHI. In his scenario, recovery.conf was created after "pg_ctl stop -m i". I'm not sure we need to support that exact scenario, but we should support backing up using a filesystem snapshot, which looks identical. This issue goes back to at least 9.0, where hot standby was introduced and we started to track when consistency is reached. In 9.1 and 9.2, we would open up for hot standby too early, and queries could briefly see an inconsistent state. But 9.2 made it more visible, as we started to PANIC if we see a reference to a non-existing page during recovery, if we've already reached consistency. This is a fairly big patch, so back-patch to 9.2 only, where the issue is more visible. We can consider back-patching further after this has received some more testing in 9.2 and master. |
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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: http://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. Changes between all PostgreSQL releases are recorded in the file HISTORY. 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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.