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Commitbe74b94

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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 parentf9b4464 commitbe74b94

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3 files changed

+18
-46
lines changed

3 files changed

+18
-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
@@ -6108,18 +6108,13 @@ heap_inplace_update_and_unlock(Relation relation,
61086108
HeapTupleHeaderhtup=oldtup->t_data;
61096109
uint32oldlen;
61106110
uint32newlen;
6111-
char*dst;
6112-
char*src;
61136111

61146112
Assert(ItemPointerEquals(&oldtup->t_self,&tuple->t_self));
61156113
oldlen=oldtup->t_len-htup->t_hoff;
61166114
newlen=tuple->t_len-tuple->t_data->t_hoff;
61176115
if (oldlen!=newlen||htup->t_hoff!=tuple->t_data->t_hoff)
61186116
elog(ERROR,"wrong tuple length");
61196117

6120-
dst= (char*)htup+htup->t_hoff;
6121-
src= (char*)tuple->t_data+tuple->t_data->t_hoff;
6122-
61236118
/*
61246119
* Construct shared cache inval if necessary. Note that because we only
61256120
* pass the new version of the tuple, this mustn't be used for any
@@ -6138,15 +6133,15 @@ heap_inplace_update_and_unlock(Relation relation,
61386133
*/
61396134
PreInplace_Inval();
61406135

6136+
/* NO EREPORT(ERROR) from here till changes are logged */
6137+
START_CRIT_SECTION();
6138+
6139+
memcpy((char*)htup+htup->t_hoff,
6140+
(char*)tuple->t_data+tuple->t_data->t_hoff,
6141+
newlen);
6142+
61416143
/*----------
6142-
* NO EREPORT(ERROR) from here till changes are complete
6143-
*
6144-
* Our buffer lock won't stop a reader having already pinned and checked
6145-
* visibility for this tuple. Hence, we write WAL first, then mutate the
6146-
* buffer. Like in MarkBufferDirtyHint() or RecordTransactionCommit(),
6147-
* checkpoint delay makes that acceptable. With the usual order of
6148-
* changes, a crash after memcpy() and before XLogInsert() could allow
6149-
* datfrozenxid to overtake relfrozenxid:
6144+
* XXX A crash here can allow datfrozenxid() to get ahead of relfrozenxid:
61506145
*
61516146
* ["D" is a VACUUM (ONLY_DATABASE_STATS)]
61526147
* ["R" is a VACUUM tbl]
@@ -6156,57 +6151,31 @@ heap_inplace_update_and_unlock(Relation relation,
61566151
* D: raise pg_database.datfrozenxid, XLogInsert(), finish
61576152
* [crash]
61586153
* [recovery restores datfrozenxid w/o relfrozenxid]
6159-
*
6160-
* Like in MarkBufferDirtyHint() subroutine XLogSaveBufferForHint(), copy
6161-
* the buffer to the stack before logging. Here, that facilitates a FPI
6162-
* of the post-mutation block before we accept other sessions seeing it.
61636154
*/
6164-
Assert(!MyProc->delayChkpt);
6165-
START_CRIT_SECTION();
6166-
MyProc->delayChkpt= true;
6155+
6156+
MarkBufferDirty(buffer);
61676157

61686158
/* XLOG stuff */
61696159
if (RelationNeedsWAL(relation))
61706160
{
61716161
xl_heap_inplacexlrec;
6172-
PGAlignedBlockcopied_buffer;
6173-
char*origdata= (char*)BufferGetBlock(buffer);
6174-
Pagepage=BufferGetPage(buffer);
6175-
uint16lower= ((PageHeader)page)->pd_lower;
6176-
uint16upper= ((PageHeader)page)->pd_upper;
6177-
uintptr_tdst_offset_in_block;
6178-
RelFileNodernode;
6179-
ForkNumberforkno;
6180-
BlockNumberblkno;
61816162
XLogRecPtrrecptr;
61826163

61836164
xlrec.offnum=ItemPointerGetOffsetNumber(&tuple->t_self);
61846165

61856166
XLogBeginInsert();
61866167
XLogRegisterData((char*)&xlrec,SizeOfHeapInplace);
61876168

6188-
/* register block matching what buffer will look like after changes */
6189-
memcpy(copied_buffer.data,origdata,lower);
6190-
memcpy(copied_buffer.data+upper,origdata+upper,BLCKSZ-upper);
6191-
dst_offset_in_block=dst-origdata;
6192-
memcpy(copied_buffer.data+dst_offset_in_block,src,newlen);
6193-
BufferGetTag(buffer,&rnode,&forkno,&blkno);
6194-
Assert(forkno==MAIN_FORKNUM);
6195-
XLogRegisterBlock(0,&rnode,forkno,blkno,copied_buffer.data,
6196-
REGBUF_STANDARD);
6197-
XLogRegisterBufData(0,src,newlen);
6169+
XLogRegisterBuffer(0,buffer,REGBUF_STANDARD);
6170+
XLogRegisterBufData(0, (char*)htup+htup->t_hoff,newlen);
61986171

61996172
/* inplace updates aren't decoded atm, don't log the origin */
62006173

62016174
recptr=XLogInsert(RM_HEAP_ID,XLOG_HEAP_INPLACE);
62026175

6203-
PageSetLSN(page,recptr);
6176+
PageSetLSN(BufferGetPage(buffer),recptr);
62046177
}
62056178

6206-
memcpy(dst,src,newlen);
6207-
6208-
MarkBufferDirty(buffer);
6209-
62106179
LockBuffer(buffer,BUFFER_LOCK_UNLOCK);
62116180

62126181
/*
@@ -6219,7 +6188,6 @@ heap_inplace_update_and_unlock(Relation relation,
62196188
*/
62206189
AtInplace_Inval();
62216190

6222-
MyProc->delayChkpt= false;
62236191
END_CRIT_SECTION();
62246192
UnlockTuple(relation,&tuple->t_self,InplaceUpdateTupleLock);
62256193

‎src/backend/access/transam/xloginsert.c

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -269,6 +269,8 @@ XLogRegisterBlock(uint8 block_id, RelFileNode *rnode, ForkNumber forknum,
269269
{
270270
registered_buffer*regbuf;
271271

272+
/* This is currently only used to WAL-log a full-page image of a page */
273+
Assert(flags&REGBUF_FORCE_IMAGE);
272274
Assert(begininsert_called);
273275

274276
if (block_id >=max_registered_block_id)

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