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Commit5e503e1

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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 parentcd64941 commit5e503e1

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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
@@ -6139,18 +6139,13 @@ heap_inplace_update_and_unlock(Relation relation,
61396139
HeapTupleHeaderhtup=oldtup->t_data;
61406140
uint32oldlen;
61416141
uint32newlen;
6142-
char*dst;
6143-
char*src;
61446142

61456143
Assert(ItemPointerEquals(&oldtup->t_self,&tuple->t_self));
61466144
oldlen=oldtup->t_len-htup->t_hoff;
61476145
newlen=tuple->t_len-tuple->t_data->t_hoff;
61486146
if (oldlen!=newlen||htup->t_hoff!=tuple->t_data->t_hoff)
61496147
elog(ERROR,"wrong tuple length");
61506148

6151-
dst= (char*)htup+htup->t_hoff;
6152-
src= (char*)tuple->t_data+tuple->t_data->t_hoff;
6153-
61546149
/*
61556150
* Construct shared cache inval if necessary. Note that because we only
61566151
* pass the new version of the tuple, this mustn't be used for any
@@ -6169,15 +6164,15 @@ heap_inplace_update_and_unlock(Relation relation,
61696164
*/
61706165
PreInplace_Inval();
61716166

6167+
/* NO EREPORT(ERROR) from here till changes are logged */
6168+
START_CRIT_SECTION();
6169+
6170+
memcpy((char*)htup+htup->t_hoff,
6171+
(char*)tuple->t_data+tuple->t_data->t_hoff,
6172+
newlen);
6173+
61726174
/*----------
6173-
* NO EREPORT(ERROR) from here till changes are complete
6174-
*
6175-
* Our buffer lock won't stop a reader having already pinned and checked
6176-
* visibility for this tuple. Hence, we write WAL first, then mutate the
6177-
* buffer. Like in MarkBufferDirtyHint() or RecordTransactionCommit(),
6178-
* checkpoint delay makes that acceptable. With the usual order of
6179-
* changes, a crash after memcpy() and before XLogInsert() could allow
6180-
* datfrozenxid to overtake relfrozenxid:
6175+
* XXX A crash here can allow datfrozenxid() to get ahead of relfrozenxid:
61816176
*
61826177
* ["D" is a VACUUM (ONLY_DATABASE_STATS)]
61836178
* ["R" is a VACUUM tbl]
@@ -6187,57 +6182,31 @@ heap_inplace_update_and_unlock(Relation relation,
61876182
* D: raise pg_database.datfrozenxid, XLogInsert(), finish
61886183
* [crash]
61896184
* [recovery restores datfrozenxid w/o relfrozenxid]
6190-
*
6191-
* Like in MarkBufferDirtyHint() subroutine XLogSaveBufferForHint(), copy
6192-
* the buffer to the stack before logging. Here, that facilitates a FPI
6193-
* of the post-mutation block before we accept other sessions seeing it.
61946185
*/
6195-
Assert(!MyPgXact->delayChkpt);
6196-
START_CRIT_SECTION();
6197-
MyPgXact->delayChkpt= true;
6186+
6187+
MarkBufferDirty(buffer);
61986188

61996189
/* XLOG stuff */
62006190
if (RelationNeedsWAL(relation))
62016191
{
62026192
xl_heap_inplacexlrec;
6203-
PGAlignedBlockcopied_buffer;
6204-
char*origdata= (char*)BufferGetBlock(buffer);
6205-
Pagepage=BufferGetPage(buffer);
6206-
uint16lower= ((PageHeader)page)->pd_lower;
6207-
uint16upper= ((PageHeader)page)->pd_upper;
6208-
uintptr_tdst_offset_in_block;
6209-
RelFileNodernode;
6210-
ForkNumberforkno;
6211-
BlockNumberblkno;
62126193
XLogRecPtrrecptr;
62136194

62146195
xlrec.offnum=ItemPointerGetOffsetNumber(&tuple->t_self);
62156196

62166197
XLogBeginInsert();
62176198
XLogRegisterData((char*)&xlrec,SizeOfHeapInplace);
62186199

6219-
/* register block matching what buffer will look like after changes */
6220-
memcpy(copied_buffer.data,origdata,lower);
6221-
memcpy(copied_buffer.data+upper,origdata+upper,BLCKSZ-upper);
6222-
dst_offset_in_block=dst-origdata;
6223-
memcpy(copied_buffer.data+dst_offset_in_block,src,newlen);
6224-
BufferGetTag(buffer,&rnode,&forkno,&blkno);
6225-
Assert(forkno==MAIN_FORKNUM);
6226-
XLogRegisterBlock(0,&rnode,forkno,blkno,copied_buffer.data,
6227-
REGBUF_STANDARD);
6228-
XLogRegisterBufData(0,src,newlen);
6200+
XLogRegisterBuffer(0,buffer,REGBUF_STANDARD);
6201+
XLogRegisterBufData(0, (char*)htup+htup->t_hoff,newlen);
62296202

62306203
/* inplace updates aren't decoded atm, don't log the origin */
62316204

62326205
recptr=XLogInsert(RM_HEAP_ID,XLOG_HEAP_INPLACE);
62336206

6234-
PageSetLSN(page,recptr);
6207+
PageSetLSN(BufferGetPage(buffer),recptr);
62356208
}
62366209

6237-
memcpy(dst,src,newlen);
6238-
6239-
MarkBufferDirty(buffer);
6240-
62416210
LockBuffer(buffer,BUFFER_LOCK_UNLOCK);
62426211

62436212
/*
@@ -6250,7 +6219,6 @@ heap_inplace_update_and_unlock(Relation relation,
62506219
*/
62516220
AtInplace_Inval();
62526221

6253-
MyPgXact->delayChkpt= false;
62546222
END_CRIT_SECTION();
62556223
UnlockTuple(relation,&tuple->t_self,InplaceUpdateTupleLock);
62566224

‎src/backend/access/transam/xloginsert.c

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -268,6 +268,8 @@ XLogRegisterBlock(uint8 block_id, RelFileNode *rnode, ForkNumber forknum,
268268
{
269269
registered_buffer*regbuf;
270270

271+
/* This is currently only used to WAL-log a full-page image of a page */
272+
Assert(flags&REGBUF_FORCE_IMAGE);
271273
Assert(begininsert_called);
272274

273275
if (block_id >=max_registered_block_id)

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