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Commitbfc79ee

Browse files
simonat2ndQuadrantkelvich
authored andcommitted
Don’t push nextid too far forwards in recovery
Doing so allows various crash possibilities. Fix by avoidinghaving PrescanPreparedTransactions() incrementShmemVariableCache->nextXid when it has no 2PC filesBug found by Jeff Janes, diagnosis and patch by Pavan Deolasee,then patch re-designed for clarity and full accuracy byMichael Paquier.Reported-by: Jeff JanesAuthor: Pavan Deolasee, Michael PaquierDiscussion:https://postgr.es/m/CAMkU=1zMLnH_i1-PVQ-biZzvNx7VcuatriquEnh7HNk6K8Ss3Q@mail.gmail.com
1 parent84d688c commitbfc79ee

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1 file changed

+36
-41
lines changed

1 file changed

+36
-41
lines changed

‎src/backend/access/transam/twophase.c

Lines changed: 36 additions & 41 deletions
Original file line numberDiff line numberDiff line change
@@ -304,7 +304,7 @@ static void XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len);
304304
staticchar*ProcessTwoPhaseBuffer(TransactionIdxid,
305305
XLogRecPtrprepare_start_lsn,
306306
boolfromdisk,booloverwriteOK,boolsetParent,
307-
TransactionId*result,TransactionId*maxsubxid);
307+
boolsetNextXid);
308308
staticvoidMarkAsPreparingGuts(GlobalTransactiongxact,TransactionIdxid,
309309
constchar*gid,TimestampTzprepared_at,Oidowner,
310310
Oiddatabaseid);
@@ -1931,7 +1931,7 @@ restoreTwoPhaseData(void)
19311931

19321932
buf=ProcessTwoPhaseBuffer(xid,InvalidXLogRecPtr,
19331933
true, false, false,
1934-
NULL,NULL);
1934+
false);
19351935
if (buf==NULL)
19361936
continue;
19371937

@@ -1974,7 +1974,6 @@ PrescanPreparedTransactions(TransactionId **xids_p, int *nxids_p)
19741974
{
19751975
TransactionIdorigNextXid=ShmemVariableCache->nextXid;
19761976
TransactionIdresult=origNextXid;
1977-
TransactionIdmaxsubxid=origNextXid;
19781977
TransactionId*xids=NULL;
19791978
intnxids=0;
19801979
intallocsize=0;
@@ -1994,11 +1993,18 @@ PrescanPreparedTransactions(TransactionId **xids_p, int *nxids_p)
19941993
buf=ProcessTwoPhaseBuffer(xid,
19951994
gxact->prepare_start_lsn,
19961995
gxact->ondisk, false, false,
1997-
&result,&maxsubxid);
1996+
true);
19981997

19991998
if (buf==NULL)
20001999
continue;
20012000

2001+
/*
2002+
* OK, we think this file is valid. Incorporate xid into the
2003+
* running-minimum result.
2004+
*/
2005+
if (TransactionIdPrecedes(xid,result))
2006+
result=xid;
2007+
20022008
if (xids_p)
20032009
{
20042010
if (nxids==allocsize)
@@ -2027,15 +2033,6 @@ PrescanPreparedTransactions(TransactionId **xids_p, int *nxids_p)
20272033
*nxids_p=nxids;
20282034
}
20292035

2030-
/* update nextXid if needed */
2031-
if (TransactionIdFollowsOrEquals(maxsubxid,ShmemVariableCache->nextXid))
2032-
{
2033-
LWLockAcquire(XidGenLock,LW_EXCLUSIVE);
2034-
ShmemVariableCache->nextXid=maxsubxid;
2035-
TransactionIdAdvance(ShmemVariableCache->nextXid);
2036-
LWLockRelease(XidGenLock);
2037-
}
2038-
20392036
returnresult;
20402037
}
20412038

@@ -2072,7 +2069,7 @@ StandbyRecoverPreparedTransactions(bool overwriteOK)
20722069
buf=ProcessTwoPhaseBuffer(xid,
20732070
gxact->prepare_start_lsn,
20742071
gxact->ondisk,overwriteOK, true,
2075-
NULL,NULL);
2072+
false);
20762073
if (buf!=NULL)
20772074
pfree(buf);
20782075
}
@@ -2118,7 +2115,7 @@ RecoverPreparedTransactions(void)
21182115
buf=ProcessTwoPhaseBuffer(xid,
21192116
gxact->prepare_start_lsn,
21202117
gxact->ondisk, false, false,
2121-
NULL,NULL);
2118+
false);
21222119
if (buf==NULL)
21232120
continue;
21242121

@@ -2209,20 +2206,16 @@ RecoverPreparedTransactions(void)
22092206
* If setParent is true, then use the overwriteOK parameter to set up
22102207
* subtransaction parent linkages.
22112208
*
2212-
* If result and maxsubxid are not NULL, fill them up with smallest
2213-
* running transaction id (lesser than ShmemVariableCache->nextXid)
2214-
* and largest subtransaction id for this transaction respectively.
2209+
* If setNextXid is true, set ShmemVariableCache->nextXid to the newest
2210+
* value scanned.
22152211
*/
22162212
staticchar*
22172213
ProcessTwoPhaseBuffer(TransactionIdxid,
22182214
XLogRecPtrprepare_start_lsn,
22192215
boolfromdisk,booloverwriteOK,
2220-
boolsetParent,TransactionId*result,
2221-
TransactionId*maxsubxid)
2216+
boolsetParent,boolsetNextXid)
22222217
{
22232218
TransactionIdorigNextXid=ShmemVariableCache->nextXid;
2224-
TransactionIdres=InvalidTransactionId;
2225-
TransactionIdmaxsub=InvalidTransactionId;
22262219
TransactionId*subxids;
22272220
char*buf;
22282221
TwoPhaseFileHeader*hdr;
@@ -2233,11 +2226,6 @@ ProcessTwoPhaseBuffer(TransactionId xid,
22332226
if (!fromdisk)
22342227
Assert(prepare_start_lsn!=InvalidXLogRecPtr);
22352228

2236-
if (result)
2237-
res=*result;
2238-
if (maxsubxid)
2239-
maxsub=*maxsubxid;
2240-
22412229
/* Already processed? */
22422230
if (TransactionIdDidCommit(xid)||TransactionIdDidAbort(xid))
22432231
{
@@ -2319,13 +2307,6 @@ ProcessTwoPhaseBuffer(TransactionId xid,
23192307
returnNULL;
23202308
}
23212309

2322-
/*
2323-
* OK, we think this buffer is valid. Incorporate xid into the
2324-
* running-minimum result.
2325-
*/
2326-
if (TransactionIdPrecedes(xid,res))
2327-
res=xid;
2328-
23292310
/*
23302311
* Examine subtransaction XIDs ... they should all follow main
23312312
* XID, and they may force us to advance nextXid.
@@ -2338,17 +2319,31 @@ ProcessTwoPhaseBuffer(TransactionId xid,
23382319
TransactionIdsubxid=subxids[i];
23392320

23402321
Assert(TransactionIdFollows(subxid,xid));
2341-
if (TransactionIdFollowsOrEquals(subxid,maxsub))
2342-
maxsub=subxid;
2322+
2323+
/* update nextXid if needed */
2324+
if (setNextXid&&
2325+
TransactionIdFollowsOrEquals(subxid,
2326+
ShmemVariableCache->nextXid))
2327+
{
2328+
/*
2329+
* We don't expect anyone else to modify nextXid, hence we don't
2330+
* need to hold a lock while examining it. We still acquire the
2331+
* lock to modify it, though, so we recheck.
2332+
*/
2333+
LWLockAcquire(XidGenLock,LW_EXCLUSIVE);
2334+
if (TransactionIdFollowsOrEquals(subxid,
2335+
ShmemVariableCache->nextXid))
2336+
{
2337+
ShmemVariableCache->nextXid=subxid;
2338+
TransactionIdAdvance(ShmemVariableCache->nextXid);
2339+
}
2340+
LWLockRelease(XidGenLock);
2341+
}
2342+
23432343
if (setParent)
23442344
SubTransSetParent(xid,subxid,overwriteOK);
23452345
}
23462346

2347-
if (result)
2348-
*result=res;
2349-
if (maxsubxid)
2350-
*maxsubxid=maxsub;
2351-
23522347
returnbuf;
23532348
}
23542349

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