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Improve snapshot manager by keeping explicit track of snapshots.

Browse Source 
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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11
src/backend/executor/execMain.c
View File

@ -26,7 +26,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.308 2008/05/12 00:00:48 alvherre Exp $
* $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.309 2008/05/12 20:02:00 alvherre Exp $
*
*-------------------------------------------------------------------------
*/
@ -54,6 +54,7 @@
#include "utils/acl.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/snapmgr.h"
#include "utils/tqual.h"
@ -185,8 +186,8 @@ ExecutorStart(QueryDesc *queryDesc, int eflags)
/*
* Copy other important information into the EState
*/
estate->es_snapshot = queryDesc->snapshot;
estate->es_crosscheck_snapshot = queryDesc->crosscheck_snapshot;
estate->es_snapshot = RegisterSnapshot(queryDesc->snapshot);
estate->es_crosscheck_snapshot = RegisterSnapshot(queryDesc->crosscheck_snapshot);
estate->es_instrument = queryDesc->doInstrument;
/*
@ -313,6 +314,10 @@ ExecutorEnd(QueryDesc *queryDesc)
if (estate->es_select_into)
CloseIntoRel(queryDesc);
/* do away with our snapshots */
UnregisterSnapshot(estate->es_snapshot);
UnregisterSnapshot(estate->es_crosscheck_snapshot);
/*
* Must switch out of context before destroying it
*/

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;
}

373
src/backend/executor/spi.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/spi.c,v 1.194 2008/05/12 00:00:49 alvherre Exp $
* $PostgreSQL: pgsql/src/backend/executor/spi.c,v 1.195 2008/05/12 20:02:00 alvherre Exp $
*
*-------------------------------------------------------------------------
*/
@ -372,9 +372,10 @@ SPI_execp(SPIPlanPtr plan, Datum *Values, const char *Nulls, long tcount)
/*
* SPI_execute_snapshot -- identical to SPI_execute_plan, except that we allow
* the caller to specify exactly which snapshots to use. Also, the caller
* may specify that AFTER triggers should be queued as part of the outer
* query rather than being fired immediately at the end of the command.
* the caller to specify exactly which snapshots to use, which will be
* registered here. Also, the caller may specify that AFTER triggers should be
* queued as part of the outer query rather than being fired immediately at the
* end of the command.
*
* This is currently not documented in spi.sgml because it is only intended
* for use by RI triggers.
@ -1102,11 +1103,11 @@ SPI_cursor_open(const char *name, SPIPlanPtr plan,
}
/*
* Set up the snapshot to use. (PortalStart will do CopySnapshot, so we
* skip that here.)
* Set up the snapshot to use. (PortalStart will do PushActiveSnapshot, so
* we skip that here.)
*/
if (read_only)
snapshot = ActiveSnapshot;
snapshot = GetActiveSnapshot();
else
{
CommandCounterIncrement();
@ -1605,216 +1606,220 @@ _SPI_execute_plan(SPIPlanPtr plan, ParamListInfo paramLI,
Snapshot snapshot, Snapshot crosscheck_snapshot,
bool read_only, bool fire_triggers, long tcount)
{
volatile int my_res = 0;
volatile uint32 my_processed = 0;
volatile Oid my_lastoid = InvalidOid;
SPITupleTable *volatile my_tuptable = NULL;
volatile int res = 0;
Snapshot saveActiveSnapshot;
int my_res = 0;
uint32 my_processed = 0;
Oid my_lastoid = InvalidOid;
SPITupleTable *my_tuptable = NULL;
int res = 0;
bool have_active_snap = ActiveSnapshotSet();
ErrorContextCallback spierrcontext;
CachedPlan *cplan = NULL;
ListCell *lc1;
/* Be sure to restore ActiveSnapshot on error exit */
saveActiveSnapshot = ActiveSnapshot;
PG_TRY();
/*
* Setup error traceback support for ereport()
*/
spierrcontext.callback = _SPI_error_callback;
spierrcontext.arg = NULL;
spierrcontext.previous = error_context_stack;
error_context_stack = &spierrcontext;
foreach(lc1, plan->plancache_list)
{
ErrorContextCallback spierrcontext;
CachedPlan *cplan = NULL;
ListCell *lc1;
CachedPlanSource *plansource = (CachedPlanSource *) lfirst(lc1);
List *stmt_list;
ListCell *lc2;
/*
* Setup error traceback support for ereport()
*/
spierrcontext.callback = _SPI_error_callback;
spierrcontext.arg = NULL;
spierrcontext.previous = error_context_stack;
error_context_stack = &spierrcontext;
spierrcontext.arg = (void *) plansource->query_string;
foreach(lc1, plan->plancache_list)
if (plan->saved)
{
CachedPlanSource *plansource = (CachedPlanSource *) lfirst(lc1);
List *stmt_list;
ListCell *lc2;
/* Replan if needed, and increment plan refcount locally */
cplan = RevalidateCachedPlan(plansource, true);
stmt_list = cplan->stmt_list;
}
else
{
/* No replan here */
cplan = NULL;
stmt_list = plansource->plan->stmt_list;
}
spierrcontext.arg = (void *) plansource->query_string;
foreach(lc2, stmt_list)
{
Node *stmt = (Node *) lfirst(lc2);
bool canSetTag;
DestReceiver *dest;
bool pushed_active_snap = false;
if (plan->saved)
_SPI_current->processed = 0;
_SPI_current->lastoid = InvalidOid;
_SPI_current->tuptable = NULL;
if (IsA(stmt, PlannedStmt))
{
/* Replan if needed, and increment plan refcount locally */
cplan = RevalidateCachedPlan(plansource, true);
stmt_list = cplan->stmt_list;
canSetTag = ((PlannedStmt *) stmt)->canSetTag;
}
else
{
/* No replan here */
cplan = NULL;
stmt_list = plansource->plan->stmt_list;
}
/* utilities are canSetTag if only thing in list */
canSetTag = (list_length(stmt_list) == 1);
foreach(lc2, stmt_list)
{
Node *stmt = (Node *) lfirst(lc2);
bool canSetTag;
DestReceiver *dest;
_SPI_current->processed = 0;
_SPI_current->lastoid = InvalidOid;
_SPI_current->tuptable = NULL;
if (IsA(stmt, PlannedStmt))
if (IsA(stmt, CopyStmt))
{
canSetTag = ((PlannedStmt *) stmt)->canSetTag;
}
else
{
/* utilities are canSetTag if only thing in list */
canSetTag = (list_length(stmt_list) == 1);
CopyStmt *cstmt = (CopyStmt *) stmt;
if (IsA(stmt, CopyStmt))
if (cstmt->filename == NULL)
{
CopyStmt *cstmt = (CopyStmt *) stmt;
if (cstmt->filename == NULL)
{
my_res = SPI_ERROR_COPY;
goto fail;
}
}
else if (IsA(stmt, TransactionStmt))
{
my_res = SPI_ERROR_TRANSACTION;
my_res = SPI_ERROR_COPY;
goto fail;
}
}
if (read_only && !CommandIsReadOnly(stmt))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
/* translator: %s is a SQL statement name */
errmsg("%s is not allowed in a non-volatile function",
CreateCommandTag(stmt))));
/*
* If not read-only mode, advance the command counter before
* each command.
*/
if (!read_only)
CommandCounterIncrement();
dest = CreateDestReceiver(canSetTag ? DestSPI : DestNone,
NULL);
if (snapshot == InvalidSnapshot)
else if (IsA(stmt, TransactionStmt))
{
/*
* Default read_only behavior is to use the entry-time
* ActiveSnapshot; if read-write, grab a full new snap.
*/
if (read_only)
ActiveSnapshot = CopySnapshot(saveActiveSnapshot);
else
ActiveSnapshot = CopySnapshot(GetTransactionSnapshot());
}
else
{
/*
* We interpret read_only with a specified snapshot to be
* exactly that snapshot, but read-write means use the
* snap with advancing of command ID.
*/
ActiveSnapshot = CopySnapshot(snapshot);
if (!read_only)
ActiveSnapshot->curcid = GetCurrentCommandId(false);
}
if (IsA(stmt, PlannedStmt) &&
((PlannedStmt *) stmt)->utilityStmt == NULL)
{
QueryDesc *qdesc;
qdesc = CreateQueryDesc((PlannedStmt *) stmt,
ActiveSnapshot,
crosscheck_snapshot,
dest,
paramLI, false);
res = _SPI_pquery(qdesc, fire_triggers,
canSetTag ? tcount : 0);
FreeQueryDesc(qdesc);
}
else
{
ProcessUtility(stmt,
plansource->query_string,
paramLI,
false, /* not top level */
dest,
NULL);
/* Update "processed" if stmt returned tuples */
if (_SPI_current->tuptable)
_SPI_current->processed = _SPI_current->tuptable->alloced - _SPI_current->tuptable->free;
res = SPI_OK_UTILITY;
}
FreeSnapshot(ActiveSnapshot);
ActiveSnapshot = NULL;
/*
* The last canSetTag query sets the status values returned to
* the caller. Be careful to free any tuptables not returned,
* to avoid intratransaction memory leak.
*/
if (canSetTag)
{
my_processed = _SPI_current->processed;
my_lastoid = _SPI_current->lastoid;
SPI_freetuptable(my_tuptable);
my_tuptable = _SPI_current->tuptable;
my_res = res;
}
else
{
SPI_freetuptable(_SPI_current->tuptable);
_SPI_current->tuptable = NULL;
}
/* we know that the receiver doesn't need a destroy call */
if (res < 0)
{
my_res = res;
my_res = SPI_ERROR_TRANSACTION;
goto fail;
}
}
/* Done with this plan, so release refcount */
if (cplan)
ReleaseCachedPlan(cplan, true);
cplan = NULL;
if (read_only && !CommandIsReadOnly(stmt))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
/* translator: %s is a SQL statement name */
errmsg("%s is not allowed in a non-volatile function",
CreateCommandTag(stmt))));
/*
* If not read-only mode, advance the command counter after the
* last command. This ensures that its effects are visible, in
* case it was DDL that would affect the next CachedPlanSource.
* If not read-only mode, advance the command counter before
* each command.
*/
if (!read_only)
CommandCounterIncrement();
dest = CreateDestReceiver(canSetTag ? DestSPI : DestNone,
NULL);
if (snapshot == InvalidSnapshot)
{
/*
* Default read_only behavior is to use the entry-time
* ActiveSnapshot, if any; if read-write, grab a full new snap.
*/
if (read_only)
{
if (have_active_snap)
{
PushActiveSnapshot(GetActiveSnapshot());
pushed_active_snap = true;
}
}
else
{
PushActiveSnapshot(GetTransactionSnapshot());
pushed_active_snap = true;
}
}
else
{
/*
* We interpret read_only with a specified snapshot to be
* exactly that snapshot, but read-write means use the
* snap with advancing of command ID.
*/
if (read_only)
PushActiveSnapshot(snapshot);
else
PushUpdatedSnapshot(snapshot);
pushed_active_snap = true;
}
if (IsA(stmt, PlannedStmt) &&
((PlannedStmt *) stmt)->utilityStmt == NULL)
{
QueryDesc *qdesc;
Snapshot snap;
if (ActiveSnapshotSet())
snap = GetActiveSnapshot();
else
snap = InvalidSnapshot;
qdesc = CreateQueryDesc((PlannedStmt *) stmt,
snap, crosscheck_snapshot,
dest,
paramLI, false);
res = _SPI_pquery(qdesc, fire_triggers,
canSetTag ? tcount : 0);
FreeQueryDesc(qdesc);
}
else
{
ProcessUtility(stmt,
plansource->query_string,
paramLI,
false, /* not top level */
dest,
NULL);
/* Update "processed" if stmt returned tuples */
if (_SPI_current->tuptable)
_SPI_current->processed = _SPI_current->tuptable->alloced -
_SPI_current->tuptable->free;
res = SPI_OK_UTILITY;
}
if (pushed_active_snap)
PopActiveSnapshot();
/*
* The last canSetTag query sets the status values returned to
* the caller. Be careful to free any tuptables not returned,
* to avoid intratransaction memory leak.
*/
if (canSetTag)
{
my_processed = _SPI_current->processed;
my_lastoid = _SPI_current->lastoid;
SPI_freetuptable(my_tuptable);
my_tuptable = _SPI_current->tuptable;
my_res = res;
}
else
{
SPI_freetuptable(_SPI_current->tuptable);
_SPI_current->tuptable = NULL;
}
/* we know that the receiver doesn't need a destroy call */
if (res < 0)
{
my_res = res;
goto fail;
}
}
/* Done with this plan, so release refcount */
if (cplan)
ReleaseCachedPlan(cplan, true);
cplan = NULL;
/*
* If not read-only mode, advance the command counter after the
* last command. This ensures that its effects are visible, in
* case it was DDL that would affect the next CachedPlanSource.
*/
if (!read_only)
CommandCounterIncrement();
}
fail:
/* We no longer need the cached plan refcount, if any */
if (cplan)
ReleaseCachedPlan(cplan, true);
/* We no longer need the cached plan refcount, if any */
if (cplan)
ReleaseCachedPlan(cplan, true);
/*
* Pop the error context stack
*/
error_context_stack = spierrcontext.previous;
}
PG_CATCH();
{
/* Restore global vars and propagate error */
ActiveSnapshot = saveActiveSnapshot;
PG_RE_THROW();
}
PG_END_TRY();
ActiveSnapshot = saveActiveSnapshot;
/*
* Pop the error context stack
*/
error_context_stack = spierrcontext.previous;
/* Save results for caller */
SPI_processed = my_processed;