Skip site navigation (1) Skip section navigation (2)

pgsql: Take fewer snapshots.

From: Robert Haas <rhaas(at)postgresql(dot)org>
To: pgsql-committers(at)postgresql(dot)org
Subject: pgsql: Take fewer snapshots.
Date: 2011-12-21 14:22:28
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-committers
Take fewer snapshots.

When a PORTAL_ONE_SELECT query is executed, we can opportunistically
reuse the parse/plan shot for the execution phase.  This cuts down the
number of snapshots per simple query from 2 to 1 for the simple
protocol, and 3 to 2 for the extended protocol.  Since we are only
reusing a snapshot taken early in the processing of the same protocol
message, the change shouldn't be user-visible, except that the remote
possibility of the planning and execution snapshots being different is

Note that this change does not make it safe to assume that the parse/plan
snapshot will certainly be reused; that will currently only happen if
PortalStart() decides to use the PORTAL_ONE_SELECT strategy.  It might
be worth trying to provide some stronger guarantees here in the future,
but for now we don't.

Patch by me; review by Dimitri Fontaine.



Modified Files
src/backend/commands/portalcmds.c |    2 +-
src/backend/commands/prepare.c    |    2 +-
src/backend/executor/spi.c        |   18 +++++++-----------
src/backend/tcop/postgres.c       |   32 +++++++++++++++++++++-----------
src/backend/tcop/pquery.c         |   15 ++++++++-------
src/include/tcop/pquery.h         |    2 +-
6 files changed, 39 insertions(+), 32 deletions(-)

pgsql-committers by date

Next:From: Robert HaasDate: 2011-12-21 20:22:15
Subject: pgsql: Improve behavior of concurrent CLUSTER.
Previous:From: Robert HaasDate: 2011-12-21 14:14:25
Subject: pgsql: sepgsql: Check CREATE permissions for some object types.

Privacy Policy | About PostgreSQL
Copyright © 1996-2018 The PostgreSQL Global Development Group