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Commitd5be107

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Revert "WAL-log inplace update before revealing it to other sessions."
This reverts commitbfd5c6e (v17) andcounterparts in each other non-master branch. This unblocks reverting acommit on which it depends.Discussion:https://postgr.es/m/10ec0bc3-5933-1189-6bb8-5dec4114558e@gmail.com
1 parent098f234 commitd5be107

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2 files changed

+16
-46
lines changed

2 files changed

+16
-46
lines changed

‎src/backend/access/heap/README.tuplock

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -203,4 +203,6 @@ Inplace updates create an exception to the rule that tuple data won't change
203203
under a reader holding a pin. A reader of a heap_fetch() result tuple may
204204
witness a torn read. Current inplace-updated fields are aligned and are no
205205
wider than four bytes, and current readers don't need consistency across
206-
fields. Hence, they get by with just fetching each field once.
206+
fields. Hence, they get by with just fetching each field once. XXX such a
207+
caller may also read a value that has not reached WAL; see
208+
systable_inplace_update_finish().

‎src/backend/access/heap/heapam.c

Lines changed: 13 additions & 45 deletions
Original file line numberDiff line numberDiff line change
@@ -6188,18 +6188,13 @@ heap_inplace_update_and_unlock(Relation relation,
61886188
HeapTupleHeaderhtup=oldtup->t_data;
61896189
uint32oldlen;
61906190
uint32newlen;
6191-
char*dst;
6192-
char*src;
61936191

61946192
Assert(ItemPointerEquals(&oldtup->t_self,&tuple->t_self));
61956193
oldlen=oldtup->t_len-htup->t_hoff;
61966194
newlen=tuple->t_len-tuple->t_data->t_hoff;
61976195
if (oldlen!=newlen||htup->t_hoff!=tuple->t_data->t_hoff)
61986196
elog(ERROR,"wrong tuple length");
61996197

6200-
dst= (char*)htup+htup->t_hoff;
6201-
src= (char*)tuple->t_data+tuple->t_data->t_hoff;
6202-
62036198
/*
62046199
* Construct shared cache inval if necessary. Note that because we only
62056200
* pass the new version of the tuple, this mustn't be used for any
@@ -6218,15 +6213,15 @@ heap_inplace_update_and_unlock(Relation relation,
62186213
*/
62196214
PreInplace_Inval();
62206215

6216+
/* NO EREPORT(ERROR) from here till changes are logged */
6217+
START_CRIT_SECTION();
6218+
6219+
memcpy((char*)htup+htup->t_hoff,
6220+
(char*)tuple->t_data+tuple->t_data->t_hoff,
6221+
newlen);
6222+
62216223
/*----------
6222-
* NO EREPORT(ERROR) from here till changes are complete
6223-
*
6224-
* Our buffer lock won't stop a reader having already pinned and checked
6225-
* visibility for this tuple. Hence, we write WAL first, then mutate the
6226-
* buffer. Like in MarkBufferDirtyHint() or RecordTransactionCommit(),
6227-
* checkpoint delay makes that acceptable. With the usual order of
6228-
* changes, a crash after memcpy() and before XLogInsert() could allow
6229-
* datfrozenxid to overtake relfrozenxid:
6224+
* XXX A crash here can allow datfrozenxid() to get ahead of relfrozenxid:
62306225
*
62316226
* ["D" is a VACUUM (ONLY_DATABASE_STATS)]
62326227
* ["R" is a VACUUM tbl]
@@ -6236,57 +6231,31 @@ heap_inplace_update_and_unlock(Relation relation,
62366231
* D: raise pg_database.datfrozenxid, XLogInsert(), finish
62376232
* [crash]
62386233
* [recovery restores datfrozenxid w/o relfrozenxid]
6239-
*
6240-
* Like in MarkBufferDirtyHint() subroutine XLogSaveBufferForHint(), copy
6241-
* the buffer to the stack before logging. Here, that facilitates a FPI
6242-
* of the post-mutation block before we accept other sessions seeing it.
62436234
*/
6244-
Assert((MyProc->delayChkptFlags&DELAY_CHKPT_START)==0);
6245-
START_CRIT_SECTION();
6246-
MyProc->delayChkptFlags |=DELAY_CHKPT_START;
6235+
6236+
MarkBufferDirty(buffer);
62476237

62486238
/* XLOG stuff */
62496239
if (RelationNeedsWAL(relation))
62506240
{
62516241
xl_heap_inplacexlrec;
6252-
PGAlignedBlockcopied_buffer;
6253-
char*origdata= (char*)BufferGetBlock(buffer);
6254-
Pagepage=BufferGetPage(buffer);
6255-
uint16lower= ((PageHeader)page)->pd_lower;
6256-
uint16upper= ((PageHeader)page)->pd_upper;
6257-
uintptr_tdst_offset_in_block;
6258-
RelFileLocatorrlocator;
6259-
ForkNumberforkno;
6260-
BlockNumberblkno;
62616242
XLogRecPtrrecptr;
62626243

62636244
xlrec.offnum=ItemPointerGetOffsetNumber(&tuple->t_self);
62646245

62656246
XLogBeginInsert();
62666247
XLogRegisterData((char*)&xlrec,SizeOfHeapInplace);
62676248

6268-
/* register block matching what buffer will look like after changes */
6269-
memcpy(copied_buffer.data,origdata,lower);
6270-
memcpy(copied_buffer.data+upper,origdata+upper,BLCKSZ-upper);
6271-
dst_offset_in_block=dst-origdata;
6272-
memcpy(copied_buffer.data+dst_offset_in_block,src,newlen);
6273-
BufferGetTag(buffer,&rlocator,&forkno,&blkno);
6274-
Assert(forkno==MAIN_FORKNUM);
6275-
XLogRegisterBlock(0,&rlocator,forkno,blkno,copied_buffer.data,
6276-
REGBUF_STANDARD);
6277-
XLogRegisterBufData(0,src,newlen);
6249+
XLogRegisterBuffer(0,buffer,REGBUF_STANDARD);
6250+
XLogRegisterBufData(0, (char*)htup+htup->t_hoff,newlen);
62786251

62796252
/* inplace updates aren't decoded atm, don't log the origin */
62806253

62816254
recptr=XLogInsert(RM_HEAP_ID,XLOG_HEAP_INPLACE);
62826255

6283-
PageSetLSN(page,recptr);
6256+
PageSetLSN(BufferGetPage(buffer),recptr);
62846257
}
62856258

6286-
memcpy(dst,src,newlen);
6287-
6288-
MarkBufferDirty(buffer);
6289-
62906259
LockBuffer(buffer,BUFFER_LOCK_UNLOCK);
62916260

62926261
/*
@@ -6299,7 +6268,6 @@ heap_inplace_update_and_unlock(Relation relation,
62996268
*/
63006269
AtInplace_Inval();
63016270

6302-
MyProc->delayChkptFlags &= ~DELAY_CHKPT_START;
63036271
END_CRIT_SECTION();
63046272
UnlockTuple(relation,&tuple->t_self,InplaceUpdateTupleLock);
63056273

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