database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-06-27 23:21:58 +03:00
Code Activity

Take fewer snapshots.

Browse Source 
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.
This commit is contained in:
Robert Haas
2011-12-21 09:16:55 -05:00
parent e1042a3484
commit d573e239f0
6 changed files with 39 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files

32
src/backend/tcop/postgres.c
View File

@ -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
@ -1696,15 +1702,19 @@ exec_bind_message(StringInfo input_message)
cplan->stmt_list,
cplan);
/*
* 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, snapshot_set);
/* Done with the snapshot used for parameter I/O and parsing/planning */
if (snapshot_set)
PopActiveSnapshot();
/*
* And we're ready to start portal execution.
*/
PortalStart(portal, params, InvalidSnapshot);
/*
* Apply the result format requests to the portal.
*/