This problem happened recently to couple of people on various Pg support channels, so I figured I can write a bit more about it, so that in future I have a place where I can refer people to 🙂
On 6th of April 2020, Amit Kapila committed patch:
Allow autovacuum to log WAL usage statistics. This commit allows autovacuum to log WAL usage statistics added by commit df3b181499. Author: Julien Rouhaud Reviewed-by: Dilip Kumar and Amit Kapila Discussion: https://postgr.es/m/CAB-hujrP8ZfUkvL5OYETipQwA=e3n7oqHFU=4ZLxWS_Cza3kQQ@mail.gmail.com
On 6th of April 2020, Amit Kapila committed patch:
Add the option to report WAL usage in EXPLAIN and auto_explain. This commit adds a new option WAL similar to existing option BUFFERS in the EXPLAIN command. This option allows to include information on WAL record generation added by commit df3b181499 in EXPLAIN output. This also allows the WAL usage information to be displayed via the auto_explain module. A new parameter auto_explain.log_wal controls whether WAL usage statistics are printed when an execution plan is logged. This parameter has no effect unless auto_explain.log_analyze is enabled. Author: Julien Rouhaud Reviewed-by: Dilip Kumar and Amit Kapila Discussion: https://postgr.es/m/CAB-hujrP8ZfUkvL5OYETipQwA=e3n7oqHFU=4ZLxWS_Cza3kQQ@mail.gmail.com
For a long time hash indexed were not crash safe, and couldn't be used on replication slave, because they skipped WAL. Now, thanks to these two commits, it has changed:
On 14th of March 2017, Robert Haas committed patch:
hash: Add write-ahead logging support. The warning about hash indexes not being write-ahead logged and their use being discouraged has been removed. "snapshot too old" is now supported for tables with hash indexes. Most importantly, barring bugs, hash indexes will now be crash-safe and usable on standbys. This commit doesn't yet add WAL consistency checking for hash indexes, as we now have for other index types; a separate patch has been submitted to cure that lack. Amit Kapila, reviewed and slightly modified by me. The larger patch series of which this is a part has been reviewed and tested by Álvaro Herrera, Ashutosh Sharma, Mark Kirkwood, Jeff Janes, and Jesper Pedersen. Discussion: http://postgr.es/m/CAA4eK1JOBX=YU33631Qh-XivYXtPSALh514+jR8XeD7v+K3r_Q@mail.gmail.com
and then, ~ 13 hours later, Robert committed also:
hash: Support WAL consistency checking. Kuntal Ghosh, reviewed by Amit Kapila and Ashutosh Sharma, with a few tweaks by me. Discussion: http://postgr.es/m/CAGz5QCJLERUn_zoO0eDv6_Y_d0o4tNTMPeR7ivTLBg4rUrJdwg@mail.gmail.com
On 20th of October, Robert Haas committed patch:
Rename "pg_xlog" directory to "pg_wal". "xlog" is not a particularly clear abbreviation for "write-ahead log", and it sometimes confuses users into believe that the contents of the "pg_xlog" directory are not critical data, leading to unpleasant consequences. So, rename the directory to "pg_wal". This patch modifies pg_upgrade and pg_basebackup to understand both the old and new directory layouts; the former is necessary given the purpose of the tool, while the latter merely avoids an unnecessary backward-compatibility break. We may wish to consider renaming other programs, switches, and functions which still use the old "xlog" naming to also refer to "wal". However, that's still under discussion, so let's do just this much for now. Discussion: CAB7nPqTeC-8+zux8_-4ZD46V7YPwooeFxgndfsq5Rg8ibLVm1A@mail.gmail.com Michael Paquier
On 22nd of August, Alvaro Herrera committed patch:
Implement ALTER TABLE .. SET LOGGED / UNLOGGED This enables changing permanent (logged) tables to unlogged and vice-versa. (Docs for ALTER TABLE / SET TABLESPACE got shuffled in an order that hopefully makes more sense than the original.) Author: Fabrízio de Royes Mello Reviewed by: Christoph Berg, Andres Freund, Thom Brown Some tweaking by Álvaro Herrera
On 11th of December, Robert Haas committed patch:
Add new wal_level, logical, sufficient for logical decoding. When wal_level=logical, we'll log columns from the old tuple as configured by the REPLICA IDENTITY facility added in commit <a class="text" href="/gitweb/?p=postgresql.git;a=object;h=07cacba983ef79be4a84fcd0e0ca3b5fcb85dd65">07cacba983ef79be4a84fcd0e0ca3b5fcb85dd65</a>. This makes it possible a properly-configured logical replication solution to correctly follow table updates even if they change the chosen key columns, or, with REPLICA IDENTITY FULL, even if the table has no key at all. Note that updates which do not modify the replica identity column won't log anything extra, making the choice of a good key (i.e. one that will rarely be changed) important to performance when wal_level=logical is configured. Each insert, update, or delete to a catalog table will also log the CMIN and/or CMAX values of stamped by the current transaction. This is necessary because logical decoding will require access to historical snapshots of the catalog in order to decode some data types, and the CMIN/CMAX values that we may need in order to judge row visibility may have been overwritten by the time we need them. Andres Freund, reviewed in various versions by myself, Heikki Linnakangas, KONDO Mitsumasa, and many others.
Just released new version of OmniPITR.
This version has one important new feature: when you're calling omnipitr-backup-slave, it will make backups only of required xlog files, and not, as previously, of all in walarchive directory.
This is important, especially in case you have multiple slaves, or you keep shared long-term walarchive. Previously – backups would get all files from walarchive (-s option to omnipitr-backup-slave), but now, it picks just the ones that are needed.
On somehow related note – I will be working now, finally, to get omnipitr-monitor functionality working.
On 25th of January, Simon Riggs committed patch:
Allow pg_basebackup from standby node with safety checking. Base backup follows recommended procedure, plus goes to great lengths to ensure that partial page writes are avoided. Jun Ishizuka and Fujii Masao, with minor modifications