From 47df4f668826c0646ae30d37971e4ff15e77b3e3 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Wed, 30 Jan 2008 18:35:55 +0000 Subject: Add a GUC variable "synchronize_seqscans" to allow clients to disable the new synchronized-scanning behavior, and make pg_dump disable sync scans so that it will reliably preserve row ordering. Per recent discussions. --- doc/src/sgml/config.sgml | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) (limited to 'doc/src') diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 30ca1c219c9..05996b49108 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -1,4 +1,4 @@ - + Server Configuration @@ -4611,6 +4611,28 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir' + + synchronize_seqscans (boolean) + + synchronize_seqscans configuration parameter + + + + This allows sequential scans of large tables to synchronize with each + other, so that concurrent scans read the same block at about the + same time and hence share the I/O workload. When this is enabled, + a scan might start in the middle of the table and then wrap + around the end to cover all rows, so as to synchronize with the + activity of scans already in progress. This can result in + unpredictable changes in the row ordering returned by queries that + have no ORDER BY clause. Setting this parameter to + off ensures the pre-8.3 behavior in which a sequential + scan always starts from the beginning of the table. The default + is on. + + + + -- cgit v1.2.3