From d573e239f03506920938bf0be56c868d9c3416da Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Wed, 21 Dec 2011 09:16:55 -0500 Subject: 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 eliminated. 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. --- src/backend/tcop/postgres.c | 32 +++++++++++++++++++++----------- 1 file changed, 21 insertions(+), 11 deletions(-) (limited to 'src/backend/tcop/postgres.c') diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c index 5bb16e010cc..f789a1e6276 100644 --- a/src/backend/tcop/postgres.c +++ b/src/backend/tcop/postgres.c @@ -943,10 +943,6 @@ exec_simple_query(const char *query_string) plantree_list = pg_plan_queries(querytree_list, 0, NULL); - /* Done with the snapshot used for parsing/planning */ - if (snapshot_set) - PopActiveSnapshot(); - /* If we got a cancel signal in analysis or planning, quit */ CHECK_FOR_INTERRUPTS(); @@ -971,9 +967,19 @@ exec_simple_query(const char *query_string) NULL); /* - * Start the portal. No parameters here. + * Start the portal. + * + * If we took a snapshot for parsing/planning, the portal may be + * able to reuse it for the execution phase. Currently, this will only + * happen in PORTAL_ONE_SELECT mode. But even if PortalStart doesn't + * end up being able to do this, keeping the parse/plan snapshot around + * until after we start the portal doesn't cost much. */ - PortalStart(portal, NULL, InvalidSnapshot); + PortalStart(portal, NULL, snapshot_set); + + /* Done with the snapshot used for parsing/planning */ + if (snapshot_set) + PopActiveSnapshot(); /* * Select the appropriate output format: text unless we are doing a @@ -1696,14 +1702,18 @@ exec_bind_message(StringInfo input_message) cplan->stmt_list, cplan); - /* Done with the snapshot used for parameter I/O and parsing/planning */ - if (snapshot_set) - PopActiveSnapshot(); - /* * And we're ready to start portal execution. + * + * If we took a snapshot for parsing/planning, we'll try to reuse it + * for query execution (currently, reuse will only occur if + * PORTAL_ONE_SELECT mode is chosen). */ - PortalStart(portal, params, InvalidSnapshot); + PortalStart(portal, params, snapshot_set); + + /* Done with the snapshot used for parameter I/O and parsing/planning */ + if (snapshot_set) + PopActiveSnapshot(); /* * Apply the result format requests to the portal. -- cgit v1.2.3