From 691d99de386aa1f5a858e04634dbaaba48488ef8 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sat, 7 May 2016 13:16:50 -0400 Subject: Docs: improve warnings about nextval() not producing gapless sequences. In the documentation for nextval(), point out explicitly that INSERT ... ON CONFLICT will call nextval() if needed for the insertion case, whether or not it ends up following the ON CONFLICT path. This seems to be a matter of some confusion, cf bug #14126, so let's be clear about it. Also mention the issue in the CREATE SEQUENCE reference page, since that is another place where people might expect such things to be covered. Minor wording improvements nearby, as well. Back-patch to 9.5 where ON CONFLICT was introduced. --- doc/src/sgml/ref/create_sequence.sgml | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'doc/src/sgml/ref/create_sequence.sgml') diff --git a/doc/src/sgml/ref/create_sequence.sgml b/doc/src/sgml/ref/create_sequence.sgml index 9e364ff2409..c9591462eed 100644 --- a/doc/src/sgml/ref/create_sequence.sgml +++ b/doc/src/sgml/ref/create_sequence.sgml @@ -239,6 +239,16 @@ SELECT * FROM name; (-9223372036854775808 to 9223372036854775807). + + Because nextval and setval calls are never + rolled back, sequence objects cannot be used if gapless + assignment of sequence numbers is needed. It is possible to build + gapless assignment by using exclusive locking of a table containing a + counter; but this solution is much more expensive than sequence + objects, especially if many transactions need sequence numbers + concurrently. + + Unexpected results might be obtained if a cache setting greater than one is -- cgit v1.2.3