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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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106
src/backend/executor/functions.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/functions.c,v 1.124 2008/03/26 18:48:59 alvherre Exp $
* $PostgreSQL: pgsql/src/backend/executor/functions.c,v 1.125 2008/05/12 20:02:00 alvherre Exp $
*
*-------------------------------------------------------------------------
*/
@ -295,15 +295,14 @@ postquel_start(execution_state *es, SQLFunctionCachePtr fcache)
* In a read-only function, use the surrounding query's snapshot;
* otherwise take a new snapshot for each query. The snapshot should
* include a fresh command ID so that all work to date in this transaction
* is visible. We copy in both cases so that postquel_end can
* unconditionally do FreeSnapshot.
* is visible.
*/
if (fcache->readonly_func)
snapshot = CopySnapshot(ActiveSnapshot);
snapshot = GetActiveSnapshot();
else
{
CommandCounterIncrement();
snapshot = CopySnapshot(GetTransactionSnapshot());
snapshot = GetTransactionSnapshot();
}
if (IsA(es->stmt, PlannedStmt))
@ -340,56 +339,44 @@ static TupleTableSlot *
postquel_getnext(execution_state *es, SQLFunctionCachePtr fcache)
{
TupleTableSlot *result;
Snapshot saveActiveSnapshot;
long count;
/* Make our snapshot the active one for any called functions */
saveActiveSnapshot = ActiveSnapshot;
PG_TRY();
{
ActiveSnapshot = es->qd->snapshot;
PushActiveSnapshot(es->qd->snapshot);
if (es->qd->utilitystmt)
{
/* ProcessUtility needs the PlannedStmt for DECLARE CURSOR */
ProcessUtility((es->qd->plannedstmt ?
(Node *) es->qd->plannedstmt :
es->qd->utilitystmt),
fcache->src,
es->qd->params,
false, /* not top level */
es->qd->dest,
NULL);
result = NULL;
}
if (es->qd->utilitystmt)
{
/* ProcessUtility needs the PlannedStmt for DECLARE CURSOR */
ProcessUtility((es->qd->plannedstmt ?
(Node *) es->qd->plannedstmt :
es->qd->utilitystmt),
fcache->src,
es->qd->params,
false, /* not top level */
es->qd->dest,
NULL);
result = NULL;
}
else
{
/*
* If it's the function's last command, and it's a SELECT, fetch
* one row at a time so we can return the results. Otherwise just
* run it to completion. (If we run to completion then
* ExecutorRun is guaranteed to return NULL.)
*/
if (LAST_POSTQUEL_COMMAND(es) &&
es->qd->operation == CMD_SELECT &&
es->qd->plannedstmt->utilityStmt == NULL &&
es->qd->plannedstmt->intoClause == NULL)
count = 1L;
else
{
/*
* If it's the function's last command, and it's a SELECT, fetch
* one row at a time so we can return the results. Otherwise just
* run it to completion. (If we run to completion then
* ExecutorRun is guaranteed to return NULL.)
*/
if (LAST_POSTQUEL_COMMAND(es) &&
es->qd->operation == CMD_SELECT &&
es->qd->plannedstmt->utilityStmt == NULL &&
es->qd->plannedstmt->intoClause == NULL)
count = 1L;
else
count = 0L;
count = 0L;
result = ExecutorRun(es->qd, ForwardScanDirection, count);
}
result = ExecutorRun(es->qd, ForwardScanDirection, count);
}
PG_CATCH();
{
/* Restore global vars and propagate error */
ActiveSnapshot = saveActiveSnapshot;
PG_RE_THROW();
}
PG_END_TRY();
ActiveSnapshot = saveActiveSnapshot;
PopActiveSnapshot();
return result;
}
@ -397,8 +384,6 @@ postquel_getnext(execution_state *es, SQLFunctionCachePtr fcache)
static void
postquel_end(execution_state *es)
{
Snapshot saveActiveSnapshot;
/* mark status done to ensure we don't do ExecutorEnd twice */
es->status = F_EXEC_DONE;
@ -406,26 +391,15 @@ postquel_end(execution_state *es)
if (es->qd->utilitystmt == NULL)
{
/* Make our snapshot the active one for any called functions */
saveActiveSnapshot = ActiveSnapshot;
PG_TRY();
{
ActiveSnapshot = es->qd->snapshot;
PushActiveSnapshot(es->qd->snapshot);
if (es->qd->operation != CMD_SELECT)
AfterTriggerEndQuery(es->qd->estate);
ExecutorEnd(es->qd);
}
PG_CATCH();
{
/* Restore global vars and propagate error */
ActiveSnapshot = saveActiveSnapshot;
PG_RE_THROW();
}
PG_END_TRY();
ActiveSnapshot = saveActiveSnapshot;
if (es->qd->operation != CMD_SELECT)
AfterTriggerEndQuery(es->qd->estate);
ExecutorEnd(es->qd);
PopActiveSnapshot();
}
FreeSnapshot(es->qd->snapshot);
FreeQueryDesc(es->qd);
es->qd = NULL;
}