Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commit5c837f8

Browse files
committed
For inplace update durability, make heap_update() callers wait.
The previous commit fixed some ways of losing an inplace update. Itremained possible to lose one when a backend working toward aheap_update() copied a tuple into memory just before inplace update ofthat tuple. In catalogs eligible for inplace update, use LOCKTAG_TUPLEto govern admission to the steps of copying an old tuple, modifying it,and issuing heap_update(). This includes MERGE commands. To avoidchanging most of the pg_class DDL, don't require LOCKTAG_TUPLE whenholding a relation lock sufficient to exclude inplace updaters.Back-patch to v12 (all supported versions). In v13 and v12, "UPDATEpg_class" or "UPDATE pg_database" can still lose an inplace update. Thev14+ UPDATE fix needs commit86dc900,and it wasn't worth reimplementing that fix without such infrastructure.Reviewed by Nitin Motiani and (in earlier versions) Heikki Linnakangas.Discussion:https://postgr.es/m/20231027214946.79.nmisch@google.com
1 parent8590c94 commit5c837f8

File tree

19 files changed

+490
-49
lines changed

19 files changed

+490
-49
lines changed

‎src/backend/access/heap/README.tuplock

Lines changed: 42 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -154,6 +154,48 @@ The following infomask bits are applicable:
154154
We currently never set the HEAP_XMAX_COMMITTED when the HEAP_XMAX_IS_MULTI bit
155155
is set.
156156

157+
Locking to write inplace-updated tables
158+
---------------------------------------
159+
160+
If IsInplaceUpdateRelation() returns true for a table, the table is a system
161+
catalog that receives systable_inplace_update_begin() calls. Preparing a
162+
heap_update() of these tables follows additional locking rules, to ensure we
163+
don't lose the effects of an inplace update. In particular, consider a moment
164+
when a backend has fetched the old tuple to modify, not yet having called
165+
heap_update(). Another backend's inplace update starting then can't conclude
166+
until the heap_update() places its new tuple in a buffer. We enforce that
167+
using locktags as follows. While DDL code is the main audience, the executor
168+
follows these rules to make e.g. "MERGE INTO pg_class" safer. Locking rules
169+
are per-catalog:
170+
171+
pg_class systable_inplace_update_begin() callers: before the call, acquire a
172+
lock on the relation in mode ShareUpdateExclusiveLock or stricter. If the
173+
update targets a row of RELKIND_INDEX (but not RELKIND_PARTITIONED_INDEX),
174+
that lock must be on the table. Locking the index rel is not necessary.
175+
(This allows VACUUM to overwrite per-index pg_class while holding a lock on
176+
the table alone.) systable_inplace_update_begin() acquires and releases
177+
LOCKTAG_TUPLE in InplaceUpdateTupleLock, an alias for ExclusiveLock, on each
178+
tuple it overwrites.
179+
180+
pg_class heap_update() callers: before copying the tuple to modify, take a
181+
lock on the tuple, a ShareUpdateExclusiveLock on the relation, or a
182+
ShareRowExclusiveLock or stricter on the relation.
183+
184+
SearchSysCacheLocked1() is one convenient way to acquire the tuple lock.
185+
Most heap_update() callers already hold a suitable lock on the relation for
186+
other reasons and can skip the tuple lock. If you do acquire the tuple
187+
lock, release it immediately after the update.
188+
189+
190+
pg_database: before copying the tuple to modify, all updaters of pg_database
191+
rows acquire LOCKTAG_TUPLE. (Few updaters acquire LOCKTAG_OBJECT on the
192+
database OID, so it wasn't worth extending that as a second option.)
193+
194+
Ideally, DDL might want to perform permissions checks before LockTuple(), as
195+
we do with RangeVarGetRelidExtended() callbacks. We typically don't bother.
196+
LOCKTAG_TUPLE acquirers release it after each row, so the potential
197+
inconvenience is lower.
198+
157199
Reading inplace-updated columns
158200
-------------------------------
159201

‎src/backend/access/heap/heapam.c

Lines changed: 149 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -52,6 +52,8 @@
5252
#include"access/xloginsert.h"
5353
#include"access/xlogutils.h"
5454
#include"catalog/catalog.h"
55+
#include"catalog/pg_database.h"
56+
#include"catalog/pg_database_d.h"
5557
#include"miscadmin.h"
5658
#include"pgstat.h"
5759
#include"port/atomics.h"
@@ -78,6 +80,12 @@ static XLogRecPtr log_heap_update(Relation reln, Buffer oldbuf,
7880
Buffernewbuf,HeapTupleoldtup,
7981
HeapTuplenewtup,HeapTupleold_key_tuple,
8082
boolall_visible_cleared,boolnew_all_visible_cleared);
83+
#ifdefUSE_ASSERT_CHECKING
84+
staticvoidcheck_lock_if_inplace_updateable_rel(Relationrelation,
85+
ItemPointerotid,
86+
HeapTuplenewtup);
87+
staticvoidcheck_inplace_rel_lock(HeapTupleoldtup);
88+
#endif
8189
staticBitmapset*HeapDetermineColumnsInfo(Relationrelation,
8290
Bitmapset*interesting_cols,
8391
Bitmapset*external_cols,
@@ -119,6 +127,8 @@ static HeapTuple ExtractReplicaIdentity(Relation rel, HeapTuple tup, bool key_re
119127
* heavyweight lock mode and MultiXactStatus values to use for any particular
120128
* tuple lock strength.
121129
*
130+
* These interact with InplaceUpdateTupleLock, an alias for ExclusiveLock.
131+
*
122132
* Don't look at lockstatus/updstatus directly! Use get_mxact_status_for_lock
123133
* instead.
124134
*/
@@ -3187,6 +3197,10 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
31873197
(errcode(ERRCODE_INVALID_TRANSACTION_STATE),
31883198
errmsg("cannot update tuples during a parallel operation")));
31893199

3200+
#ifdefUSE_ASSERT_CHECKING
3201+
check_lock_if_inplace_updateable_rel(relation,otid,newtup);
3202+
#endif
3203+
31903204
/*
31913205
* Fetch the list of attributes to be checked for various operations.
31923206
*
@@ -4014,6 +4028,128 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
40144028
returnTM_Ok;
40154029
}
40164030

4031+
#ifdefUSE_ASSERT_CHECKING
4032+
/*
4033+
* Confirm adequate lock held during heap_update(), per rules from
4034+
* README.tuplock section "Locking to write inplace-updated tables".
4035+
*/
4036+
staticvoid
4037+
check_lock_if_inplace_updateable_rel(Relationrelation,
4038+
ItemPointerotid,
4039+
HeapTuplenewtup)
4040+
{
4041+
/* LOCKTAG_TUPLE acceptable for any catalog */
4042+
switch (RelationGetRelid(relation))
4043+
{
4044+
caseRelationRelationId:
4045+
caseDatabaseRelationId:
4046+
{
4047+
LOCKTAGtuptag;
4048+
4049+
SET_LOCKTAG_TUPLE(tuptag,
4050+
relation->rd_lockInfo.lockRelId.dbId,
4051+
relation->rd_lockInfo.lockRelId.relId,
4052+
ItemPointerGetBlockNumber(otid),
4053+
ItemPointerGetOffsetNumber(otid));
4054+
if (LockHeldByMe(&tuptag,InplaceUpdateTupleLock))
4055+
return;
4056+
}
4057+
break;
4058+
default:
4059+
Assert(!IsInplaceUpdateRelation(relation));
4060+
return;
4061+
}
4062+
4063+
switch (RelationGetRelid(relation))
4064+
{
4065+
caseRelationRelationId:
4066+
{
4067+
/* LOCKTAG_TUPLE or LOCKTAG_RELATION ok */
4068+
Form_pg_classclassForm= (Form_pg_class)GETSTRUCT(newtup);
4069+
Oidrelid=classForm->oid;
4070+
Oiddbid;
4071+
LOCKTAGtag;
4072+
4073+
if (IsSharedRelation(relid))
4074+
dbid=InvalidOid;
4075+
else
4076+
dbid=MyDatabaseId;
4077+
4078+
if (classForm->relkind==RELKIND_INDEX)
4079+
{
4080+
Relationirel=index_open(relid,AccessShareLock);
4081+
4082+
SET_LOCKTAG_RELATION(tag,dbid,irel->rd_index->indrelid);
4083+
index_close(irel,AccessShareLock);
4084+
}
4085+
else
4086+
SET_LOCKTAG_RELATION(tag,dbid,relid);
4087+
4088+
if (!LockHeldByMe(&tag,ShareUpdateExclusiveLock)&&
4089+
!LockOrStrongerHeldByMe(&tag,ShareRowExclusiveLock))
4090+
elog(WARNING,
4091+
"missing lock for relation \"%s\" (OID %u, relkind %c) @ TID (%u,%u)",
4092+
NameStr(classForm->relname),
4093+
relid,
4094+
classForm->relkind,
4095+
ItemPointerGetBlockNumber(otid),
4096+
ItemPointerGetOffsetNumber(otid));
4097+
}
4098+
break;
4099+
caseDatabaseRelationId:
4100+
{
4101+
/* LOCKTAG_TUPLE required */
4102+
Form_pg_databasedbForm= (Form_pg_database)GETSTRUCT(newtup);
4103+
4104+
elog(WARNING,
4105+
"missing lock on database \"%s\" (OID %u) @ TID (%u,%u)",
4106+
NameStr(dbForm->datname),
4107+
dbForm->oid,
4108+
ItemPointerGetBlockNumber(otid),
4109+
ItemPointerGetOffsetNumber(otid));
4110+
}
4111+
break;
4112+
}
4113+
}
4114+
4115+
/*
4116+
* Confirm adequate relation lock held, per rules from README.tuplock section
4117+
* "Locking to write inplace-updated tables".
4118+
*/
4119+
staticvoid
4120+
check_inplace_rel_lock(HeapTupleoldtup)
4121+
{
4122+
Form_pg_classclassForm= (Form_pg_class)GETSTRUCT(oldtup);
4123+
Oidrelid=classForm->oid;
4124+
Oiddbid;
4125+
LOCKTAGtag;
4126+
4127+
if (IsSharedRelation(relid))
4128+
dbid=InvalidOid;
4129+
else
4130+
dbid=MyDatabaseId;
4131+
4132+
if (classForm->relkind==RELKIND_INDEX)
4133+
{
4134+
Relationirel=index_open(relid,AccessShareLock);
4135+
4136+
SET_LOCKTAG_RELATION(tag,dbid,irel->rd_index->indrelid);
4137+
index_close(irel,AccessShareLock);
4138+
}
4139+
else
4140+
SET_LOCKTAG_RELATION(tag,dbid,relid);
4141+
4142+
if (!LockOrStrongerHeldByMe(&tag,ShareUpdateExclusiveLock))
4143+
elog(WARNING,
4144+
"missing lock for relation \"%s\" (OID %u, relkind %c) @ TID (%u,%u)",
4145+
NameStr(classForm->relname),
4146+
relid,
4147+
classForm->relkind,
4148+
ItemPointerGetBlockNumber(&oldtup->t_self),
4149+
ItemPointerGetOffsetNumber(&oldtup->t_self));
4150+
}
4151+
#endif
4152+
40174153
/*
40184154
* Check if the specified attribute's values are the same. Subroutine for
40194155
* HeapDetermineColumnsInfo.
@@ -6039,15 +6175,21 @@ heap_inplace_lock(Relation relation,
60396175
TM_Resultresult;
60406176
boolret;
60416177

6178+
#ifdefUSE_ASSERT_CHECKING
6179+
if (RelationGetRelid(relation)==RelationRelationId)
6180+
check_inplace_rel_lock(oldtup_ptr);
6181+
#endif
6182+
60426183
Assert(BufferIsValid(buffer));
60436184

6185+
LockTuple(relation,&oldtup.t_self,InplaceUpdateTupleLock);
60446186
LockBuffer(buffer,BUFFER_LOCK_EXCLUSIVE);
60456187

60466188
/*----------
60476189
* Interpret HeapTupleSatisfiesUpdate() like heap_update() does, except:
60486190
*
60496191
* - wait unconditionally
6050-
* -notuplelocks
6192+
* -already lockedtupleabove, since inplace needs that unconditionally
60516193
* - don't recheck header after wait: simpler to defer to next iteration
60526194
* - don't try to continue even if the updater aborts: likewise
60536195
* - no crosscheck
@@ -6131,7 +6273,10 @@ heap_inplace_lock(Relation relation,
61316273
* don't bother optimizing that.
61326274
*/
61336275
if (!ret)
6276+
{
6277+
UnlockTuple(relation,&oldtup.t_self,InplaceUpdateTupleLock);
61346278
InvalidateCatalogSnapshot();
6279+
}
61356280
returnret;
61366281
}
61376282

@@ -6140,6 +6285,8 @@ heap_inplace_lock(Relation relation,
61406285
*
61416286
* The tuple cannot change size, and therefore its header fields and null
61426287
* bitmap (if any) don't change either.
6288+
*
6289+
* Since we hold LOCKTAG_TUPLE, no updater has a local copy of this tuple.
61436290
*/
61446291
void
61456292
heap_inplace_update_and_unlock(Relationrelation,
@@ -6223,6 +6370,7 @@ heap_inplace_unlock(Relation relation,
62236370
HeapTupleoldtup,Bufferbuffer)
62246371
{
62256372
LockBuffer(buffer,BUFFER_LOCK_UNLOCK);
6373+
UnlockTuple(relation,&oldtup->t_self,InplaceUpdateTupleLock);
62266374
}
62276375

62286376
/*

‎src/backend/access/index/genam.c

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -755,7 +755,9 @@ systable_endscan_ordered(SysScanDesc sysscan)
755755
*
756756
* Overwriting violates both MVCC and transactional safety, so the uses of
757757
* this function in Postgres are extremely limited. Nonetheless we find some
758-
* places to use it. Standard flow:
758+
* places to use it. See README.tuplock section "Locking to write
759+
* inplace-updated tables" and later sections for expectations of readers and
760+
* writers of a table that gets inplace updates. Standard flow:
759761
*
760762
* ... [any slow preparation not requiring oldtup] ...
761763
* systable_inplace_update_begin([...], &tup, &inplace_state);

‎src/backend/catalog/aclchk.c

Lines changed: 7 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -70,6 +70,7 @@
7070
#include"nodes/makefuncs.h"
7171
#include"parser/parse_func.h"
7272
#include"parser/parse_type.h"
73+
#include"storage/lmgr.h"
7374
#include"utils/acl.h"
7475
#include"utils/aclchk_internal.h"
7576
#include"utils/builtins.h"
@@ -1822,7 +1823,7 @@ ExecGrant_Relation(InternalGrant *istmt)
18221823
HeapTupletuple;
18231824
ListCell*cell_colprivs;
18241825

1825-
tuple=SearchSysCache1(RELOID,ObjectIdGetDatum(relOid));
1826+
tuple=SearchSysCacheLocked1(RELOID,ObjectIdGetDatum(relOid));
18261827
if (!HeapTupleIsValid(tuple))
18271828
elog(ERROR,"cache lookup failed for relation %u",relOid);
18281829
pg_class_tuple= (Form_pg_class)GETSTRUCT(tuple);
@@ -2038,6 +2039,7 @@ ExecGrant_Relation(InternalGrant *istmt)
20382039
values,nulls,replaces);
20392040

20402041
CatalogTupleUpdate(relation,&newtuple->t_self,newtuple);
2042+
UnlockTuple(relation,&tuple->t_self,InplaceUpdateTupleLock);
20412043

20422044
/* Update initial privileges for extensions */
20432045
recordExtensionInitPriv(relOid,RelationRelationId,0,new_acl);
@@ -2050,6 +2052,8 @@ ExecGrant_Relation(InternalGrant *istmt)
20502052

20512053
pfree(new_acl);
20522054
}
2055+
else
2056+
UnlockTuple(relation,&tuple->t_self,InplaceUpdateTupleLock);
20532057

20542058
/*
20552059
* Handle column-level privileges, if any were specified or implied.
@@ -2159,7 +2163,7 @@ ExecGrant_Database(InternalGrant *istmt)
21592163
Oid*newmembers;
21602164
HeapTupletuple;
21612165

2162-
tuple=SearchSysCache1(DATABASEOID,ObjectIdGetDatum(datId));
2166+
tuple=SearchSysCacheLocked1(DATABASEOID,ObjectIdGetDatum(datId));
21632167
if (!HeapTupleIsValid(tuple))
21642168
elog(ERROR,"cache lookup failed for database %u",datId);
21652169

@@ -2228,6 +2232,7 @@ ExecGrant_Database(InternalGrant *istmt)
22282232
nulls,replaces);
22292233

22302234
CatalogTupleUpdate(relation,&newtuple->t_self,newtuple);
2235+
UnlockTuple(relation,&tuple->t_self,InplaceUpdateTupleLock);
22312236

22322237
/* Update the shared dependency ACL info */
22332238
updateAclDependencies(DatabaseRelationId,pg_database_tuple->oid,0,

‎src/backend/catalog/catalog.c

Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -140,6 +140,15 @@ IsCatalogRelationOid(Oid relid)
140140
/*
141141
* IsInplaceUpdateRelation
142142
*True iff core code performs inplace updates on the relation.
143+
*
144+
*This is used for assertions and for making the executor follow the
145+
*locking protocol described at README.tuplock section "Locking to write
146+
*inplace-updated tables". Extensions may inplace-update other heap
147+
*tables, but concurrent SQL UPDATE on the same table may overwrite
148+
*those modifications.
149+
*
150+
*The executor can assume these are not partitions or partitioned and
151+
*have no triggers.
143152
*/
144153
bool
145154
IsInplaceUpdateRelation(Relationrelation)

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp