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Improve snapshot manager by keeping explicit track of snapshots.

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There are two ways to track a snapshot: there's the "registered" list, which
is used for arbitrary long-lived snapshots; and there's the "active stack",
which is used for the snapshot that is considered "active" at any time.
This also allows users of snapshots to stop worrying about snapshot memory
allocation and freeing, and about using PG_TRY blocks around ActiveSnapshot
assignment.  This is all done automatically now.

As a consequence, this allows us to reset MyProc->xmin when there are no
more snapshots registered in the current backend, reducing the impact that
long-running transactions have on VACUUM.
This commit is contained in:
Alvaro Herrera
2008-05-12 20:02:02 +00:00
parent aa82790fca
commit 5da9da71c4
27 changed files with 995 additions and 551 deletions
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18
src/backend/commands/copy.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/copy.c,v 1.298 2008/03/26 18:48:59 alvherre Exp $
* $PostgreSQL: pgsql/src/backend/commands/copy.c,v 1.299 2008/05/12 20:01:59 alvherre Exp $
*
*-------------------------------------------------------------------------
*/
@ -1044,21 +1044,18 @@ DoCopy(const CopyStmt *stmt, const char *queryString)
plan = planner(query, 0, NULL);
/*
* Update snapshot command ID to ensure this query sees results of any
* previously executed queries. (It's a bit cheesy to modify
* ActiveSnapshot without making a copy, but for the limited ways in
* which COPY can be invoked, I think it's OK, because the active
* snapshot shouldn't be shared with anything else anyway.)
* Use a snapshot with an updated command ID to ensure this query sees
* results of any previously executed queries.
*/
ActiveSnapshot->curcid = GetCurrentCommandId(false);
PushUpdatedSnapshot(GetActiveSnapshot());
/* Create dest receiver for COPY OUT */
dest = CreateDestReceiver(DestCopyOut, NULL);
((DR_copy *) dest)->cstate = cstate;
/* Create a QueryDesc requesting no output */
cstate->queryDesc = CreateQueryDesc(plan,
ActiveSnapshot, InvalidSnapshot,
cstate->queryDesc = CreateQueryDesc(plan, GetActiveSnapshot(),
InvalidSnapshot,
dest, NULL, false);
/*
@ -1161,6 +1158,7 @@ DoCopy(const CopyStmt *stmt, const char *queryString)
/* Close down the query and free resources. */
ExecutorEnd(cstate->queryDesc);
FreeQueryDesc(cstate->queryDesc);
PopActiveSnapshot();
}
/* Clean up storage (probably not really necessary) */
@ -1390,7 +1388,7 @@ CopyTo(CopyState cstate)
values = (Datum *) palloc(num_phys_attrs * sizeof(Datum));
nulls = (bool *) palloc(num_phys_attrs * sizeof(bool));
scandesc = heap_beginscan(cstate->rel, ActiveSnapshot, 0, NULL);
scandesc = heap_beginscan(cstate->rel, GetActiveSnapshot(), 0, NULL);
while ((tuple = heap_getnext(scandesc, ForwardScanDirection)) != NULL)
{