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Take fewer snapshots.

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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
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2
src/include/tcop/pquery.h
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@@ -28,7 +28,7 @@ extern List *FetchPortalTargetList(Portal portal);
extern List *FetchStatementTargetList(Node *stmt);
extern void PortalStart(Portal portal, ParamListInfo params,
Snapshot snapshot);
bool use_active_snapshot);
extern void PortalSetResultFormat(Portal portal, int nFormats,
int16 *formats);