database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-28 23:42:10 +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

15
src/backend/tcop/pquery.c
View File

@ -446,16 +446,17 @@ FetchStatementTargetList(Node *stmt)
* the query, they must be passed in here (caller is responsible for
* giving them appropriate lifetime).
*
* The caller can optionally pass a snapshot to be used; pass InvalidSnapshot
* for the normal behavior of setting a new snapshot. This parameter is
* presently ignored for non-PORTAL_ONE_SELECT portals (it's only intended
* to be used for cursors).
* The use_active_snapshot parameter is currently used only for
* PORTAL_ONE_SELECT portals. If it is true, the active snapshot will
* be used when starting up the executor; if false, a new snapshot will
* be taken. This is used both for cursors and to avoid taking an entirely
* new snapshot when it isn't necessary.
*
* On return, portal is ready to accept PortalRun() calls, and the result
* tupdesc (if any) is known.
*/
void
PortalStart(Portal portal, ParamListInfo params, Snapshot snapshot)
PortalStart(Portal portal, ParamListInfo params, bool use_active_snapshot)
{
Portal saveActivePortal;
ResourceOwner saveResourceOwner;
@ -497,8 +498,8 @@ PortalStart(Portal portal, ParamListInfo params, Snapshot snapshot)
case PORTAL_ONE_SELECT:
/* Must set snapshot before starting executor. */
if (snapshot)
PushActiveSnapshot(snapshot);
if (use_active_snapshot)
PushActiveSnapshot(GetActiveSnapshot());
else
PushActiveSnapshot(GetTransactionSnapshot());