Peter Eisentraut f8dc1985fd Fix ALTER SEQUENCE locking ... In 1753b1b027, the pg_sequence system catalog was introduced. This made sequence metadata changes transactional, while the actual sequence values are still behaving nontransactionally. This requires some refinement in how ALTER SEQUENCE, which operates on both, locks the sequence and the catalog. The main problems were: - Concurrent ALTER SEQUENCE causes "tuple concurrently updated" error, caused by updates to pg_sequence catalog. - Sequence WAL writes and catalog updates are not protected by same lock, which could lead to inconsistent recovery order. - nextval() disregarding uncommitted ALTER SEQUENCE changes. To fix, nextval() and friends now lock the sequence using RowExclusiveLock instead of AccessShareLock. ALTER SEQUENCE locks the sequence using ShareRowExclusiveLock. This means that nextval() and ALTER SEQUENCE block each other, and ALTER SEQUENCE on the same sequence blocks itself. (This was already the case previously for the OWNER TO, RENAME, and SET SCHEMA variants.) Also, rearrange some code so that the entire AlterSequence is protected by the lock on the sequence. As an exception, use reduced locking for ALTER SEQUENCE ... RESTART. Since that is basically a setval(), it does not require the full locking of other ALTER SEQUENCE actions. So check whether we are only running a RESTART and run with less locking if so. Reviewed-by: Michael Paquier <michael.paquier@gmail.com> Reported-by: Jason Petersen <jason@citusdata.com> Reported-by: Andres Freund <andres@anarazel.de>		2017-05-15 10:19:57 -04:00
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src	Fix ALTER SEQUENCE locking	2017-05-15 10:19:57 -04:00
bug.template	Stamp HEAD as 10devel.	2016-08-15 13:49:49 -04:00
KNOWN_BUGS	Remove extra newlines at end and beginning of files, add missing newlines	2010-08-19 05:57:36 +00:00
Makefile	Remove maintainer-check target, fold into normal build	2013-10-10 20:11:56 -04:00
MISSING_FEATURES	Remove extra newlines at end and beginning of files, add missing newlines	2010-08-19 05:57:36 +00:00
TODO	Update URL.	2008-08-21 20:15:31 +00:00