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Set cutoff xmin more aggressively when vacuuming a temporary table. 

Since other sessions aren't allowed to look into a temporary table
of our own session, we do not need to worry about the global xmin
horizon when setting the vacuum XID cutoff.  Indeed, if we're not
inside a transaction block, we may set oldestXmin to be the next
XID, because there cannot be any in-doubt tuples in a temp table,
nor any tuples that are dead but still visible to some snapshot of
our transaction.  (VACUUM, of course, is never inside a transaction
block; but we need to test that because CLUSTER shares the same code.)

This approach allows us to always clean out a temp table completely
during VACUUM, independently of concurrent activity.  Aside from
being useful in its own right, that simplifies building reproducible
test cases.

Discussion: https://postgr.es/m/3490536.1598629609@sss.pgh.pa.us
This commit is contained in:
Tom Lane 2020-09-01 18:37:12 -04:00
parent db864c3c36
commit a7212be8b9
5 changed files with 70 additions and 36 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
src/backend/access/heap/vacuumlazy.c
View File

@ -471,6 +471,7 @@ heap_vacuum_rel(Relation onerel, VacuumParams *params,
params->freeze_table_age,
params->multixact_freeze_min_age,
params->multixact_freeze_table_age,
true, /* we must be a top-level command */
&OldestXmin, &FreezeLimit, &xidFullScanLimit,
&MultiXactCutoff, &mxactFullScanLimit);

28
src/backend/commands/cluster.c
View File

@ -67,10 +67,13 @@ typedef struct
} RelToCluster;
static void rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose);
static void rebuild_relation(Relation OldHeap, Oid indexOid,
bool isTopLevel, bool verbose);
static void copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex,
bool verbose, bool *pSwapToastByContent,
TransactionId *pFreezeXid, MultiXactId *pCutoffMulti);
bool isTopLevel, bool verbose,
bool *pSwapToastByContent,
TransactionId *pFreezeXid,
MultiXactId *pCutoffMulti);
static List *get_tables_to_cluster(MemoryContext cluster_context);
@ -170,7 +173,7 @@ cluster(ClusterStmt *stmt, bool isTopLevel)
table_close(rel, NoLock);
/* Do the job. */
cluster_rel(tableOid, indexOid, stmt->options);
cluster_rel(tableOid, indexOid, stmt->options, isTopLevel);
}
else
{
@ -219,7 +222,8 @@ cluster(ClusterStmt *stmt, bool isTopLevel)
PushActiveSnapshot(GetTransactionSnapshot());
/* Do the job. */
cluster_rel(rvtc->tableOid, rvtc->indexOid,
stmt->options | CLUOPT_RECHECK);
stmt->options | CLUOPT_RECHECK,
isTopLevel);
PopActiveSnapshot();
CommitTransactionCommand();
}
@ -250,7 +254,7 @@ cluster(ClusterStmt *stmt, bool isTopLevel)
* and error messages should refer to the operation as VACUUM not CLUSTER.
*/
void
cluster_rel(Oid tableOid, Oid indexOid, int options)
cluster_rel(Oid tableOid, Oid indexOid, int options, bool isTopLevel)
{
Relation OldHeap;
bool verbose = ((options & CLUOPT_VERBOSE) != 0);
@ -400,7 +404,7 @@ cluster_rel(Oid tableOid, Oid indexOid, int options)
TransferPredicateLocksToHeapRelation(OldHeap);
/* rebuild_relation does all the dirty work */
rebuild_relation(OldHeap, indexOid, verbose);
rebuild_relation(OldHeap, indexOid, isTopLevel, verbose);
/* NB: rebuild_relation does table_close() on OldHeap */
@ -545,11 +549,12 @@ mark_index_clustered(Relation rel, Oid indexOid, bool is_internal)
*
* OldHeap: table to rebuild --- must be opened and exclusive-locked!
* indexOid: index to cluster by, or InvalidOid to rewrite in physical order.
* isTopLevel: should be passed down from ProcessUtility.
*
* NB: this routine closes OldHeap at the right time; caller should not.
*/
static void
rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose)
rebuild_relation(Relation OldHeap, Oid indexOid, bool isTopLevel, bool verbose)
{
Oid tableOid = RelationGetRelid(OldHeap);
Oid tableSpace = OldHeap->rd_rel->reltablespace;
@ -577,7 +582,7 @@ rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose)
AccessExclusiveLock);
/* Copy the heap data into the new table in the desired order */
copy_table_data(OIDNewHeap, tableOid, indexOid, verbose,
copy_table_data(OIDNewHeap, tableOid, indexOid, isTopLevel, verbose,
&swap_toast_by_content, &frozenXid, &cutoffMulti);
/*
@ -728,7 +733,8 @@ make_new_heap(Oid OIDOldHeap, Oid NewTableSpace, char relpersistence,
* *pCutoffMulti receives the MultiXactId used as a cutoff point.
*/
static void
copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex, bool verbose,
copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex,
bool isTopLevel, bool verbose,
bool *pSwapToastByContent, TransactionId *pFreezeXid,
MultiXactId *pCutoffMulti)
{
@ -826,7 +832,7 @@ copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex, bool verbose,
* Since we're going to rewrite the whole table anyway, there's no reason
* not to be aggressive about this.
*/
vacuum_set_xid_limits(OldHeap, 0, 0, 0, 0,
vacuum_set_xid_limits(OldHeap, 0, 0, 0, 0, isTopLevel,
&OldestXmin, &FreezeXid, NULL, &MultiXactCutoff,
NULL);

73
src/backend/commands/vacuum.c
View File

@ -907,6 +907,9 @@ get_all_vacuum_rels(int options)
/*
* vacuum_set_xid_limits() -- compute oldestXmin and freeze cutoff points
*
* Input parameters are the target relation, applicable freeze age settings,
* and isTopLevel which should be passed down from ProcessUtility.
*
* The output parameters are:
* - oldestXmin is the cutoff value used to distinguish whether tuples are
* DEAD or RECENTLY_DEAD (see HeapTupleSatisfiesVacuum).
@ -931,6 +934,7 @@ vacuum_set_xid_limits(Relation rel,
int freeze_table_age,
int multixact_freeze_min_age,
int multixact_freeze_table_age,
bool isTopLevel,
TransactionId *oldestXmin,
TransactionId *freezeLimit,
TransactionId *xidFullScanLimit,
@ -946,32 +950,53 @@ vacuum_set_xid_limits(Relation rel,
MultiXactId mxactLimit;
MultiXactId safeMxactLimit;
/*
* We can always ignore processes running lazy vacuum. This is because we
* use these values only for deciding which tuples we must keep in the
* tables. Since lazy vacuum doesn't write its XID anywhere (usually no
* XID assigned), it's safe to ignore it. In theory it could be
* problematic to ignore lazy vacuums in a full vacuum, but keep in mind
* that only one vacuum process can be working on a particular table at
* any time, and that each vacuum is always an independent transaction.
*/
*oldestXmin = GetOldestNonRemovableTransactionId(rel);
if (OldSnapshotThresholdActive())
if (RELATION_IS_LOCAL(rel) && !IsInTransactionBlock(isTopLevel))
{
TransactionId limit_xmin;
TimestampTz limit_ts;
/*
* If we are processing a temp relation (which by prior checks must be
* one belonging to our session), and we are not inside any
* transaction block, then there can be no tuples in the rel that are
* still in-doubt, nor can there be any that are dead but possibly
* still interesting to some snapshot our session holds. We don't
* need to care whether other sessions could see such tuples, either.
* So we can aggressively set the cutoff xmin to be the nextXid.
*/
*oldestXmin = ReadNewTransactionId();
}
else
{
/*
* Otherwise, calculate the cutoff xmin normally.
*
* We can always ignore processes running lazy vacuum. This is
* because we use these values only for deciding which tuples we must
* keep in the tables. Since lazy vacuum doesn't write its XID
* anywhere (usually no XID assigned), it's safe to ignore it. In
* theory it could be problematic to ignore lazy vacuums in a full
* vacuum, but keep in mind that only one vacuum process can be
* working on a particular table at any time, and that each vacuum is
* always an independent transaction.
*/
*oldestXmin = GetOldestNonRemovableTransactionId(rel);
if (TransactionIdLimitedForOldSnapshots(*oldestXmin, rel, &limit_xmin, &limit_ts))
if (OldSnapshotThresholdActive())
{
/*
* TODO: We should only set the threshold if we are pruning on the
* basis of the increased limits. Not as crucial here as it is for
* opportunistic pruning (which often happens at a much higher
* frequency), but would still be a significant improvement.
*/
SetOldSnapshotThresholdTimestamp(limit_ts, limit_xmin);
*oldestXmin = limit_xmin;
TransactionId limit_xmin;
TimestampTz limit_ts;
if (TransactionIdLimitedForOldSnapshots(*oldestXmin, rel,
&limit_xmin, &limit_ts))
{
/*
* TODO: We should only set the threshold if we are pruning on
* the basis of the increased limits. Not as crucial here as
* it is for opportunistic pruning (which often happens at a
* much higher frequency), but would still be a significant
* improvement.
*/
SetOldSnapshotThresholdTimestamp(limit_ts, limit_xmin);
*oldestXmin = limit_xmin;
}
}
}
@ -1905,7 +1930,7 @@ vacuum_rel(Oid relid, RangeVar *relation, VacuumParams *params)
cluster_options |= CLUOPT_VERBOSE;
/* VACUUM FULL is now a variant of CLUSTER; see cluster.c */
cluster_rel(relid, InvalidOid, cluster_options);
cluster_rel(relid, InvalidOid, cluster_options, true);
}
else
table_relation_vacuum(onerel, params, vac_strategy);

3
src/include/commands/cluster.h
View File

@ -19,7 +19,8 @@
extern void cluster(ClusterStmt *stmt, bool isTopLevel);
extern void cluster_rel(Oid tableOid, Oid indexOid, int options);
extern void cluster_rel(Oid tableOid, Oid indexOid, int options,
bool isTopLevel);
extern void check_index_is_clusterable(Relation OldHeap, Oid indexOid,
bool recheck, LOCKMODE lockmode);
extern void mark_index_clustered(Relation rel, Oid indexOid, bool is_internal);

1
src/include/commands/vacuum.h
View File

@ -267,6 +267,7 @@ extern void vacuum_set_xid_limits(Relation rel,
int freeze_min_age, int freeze_table_age,
int multixact_freeze_min_age,
int multixact_freeze_table_age,
bool isTopLevel,
TransactionId *oldestXmin,
TransactionId *freezeLimit,
TransactionId *xidFullScanLimit,