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Commit9ea7388

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Second try at fixing no-room-to-move-down PANIC in compact_fsm_storage.
Ward's report that it can still happen in RC2 forces me to realize thatthis is not a can't-happen condition after all, and that the compactioncode had better cope rather than panicking.
1 parent5392e73 commit9ea7388

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-17
lines changed

1 file changed

+47
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‎src/backend/storage/freespace/freespace.c

Lines changed: 47 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/storage/freespace/freespace.c,v 1.24 2003/10/29 17:36:57 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/storage/freespace/freespace.c,v 1.25 2003/11/26 20:50:11 tgl Exp $
1212
*
1313
*
1414
* NOTES:
@@ -1394,6 +1394,7 @@ static void
13941394
compact_fsm_storage(void)
13951395
{
13961396
intnextChunkIndex=0;
1397+
booldid_push= false;
13971398
FSMRelation*fsmrel;
13981399

13991400
for (fsmrel=FreeSpaceMap->firstRel;
@@ -1419,16 +1420,15 @@ compact_fsm_storage(void)
14191420
newAllocPages=newAlloc*INDEXCHUNKPAGES;
14201421
else
14211422
newAllocPages=newAlloc*CHUNKPAGES;
1422-
newChunkIndex=nextChunkIndex;
1423-
nextChunkIndex+=newAlloc;
14241423

14251424
/*
14261425
* Determine current size, current and new locations
14271426
*/
14281427
curChunks=fsm_current_chunks(fsmrel);
14291428
oldChunkIndex=fsmrel->firstChunk;
1430-
newLocation=FreeSpaceMap->arena+newChunkIndex*CHUNKBYTES;
14311429
oldLocation=FreeSpaceMap->arena+oldChunkIndex*CHUNKBYTES;
1430+
newChunkIndex=nextChunkIndex;
1431+
newLocation=FreeSpaceMap->arena+newChunkIndex*CHUNKBYTES;
14321432

14331433
/*
14341434
* It's possible that we have to move data down, not up, if the
@@ -1440,10 +1440,16 @@ compact_fsm_storage(void)
14401440
* more than once, so pack everything against the end of the arena
14411441
* if so.
14421442
*
1443-
* In corner cases where roundoff has affected our allocation, it's
1444-
* possible that we have to move down and compress our data too.
1445-
* Since this case is extremely infrequent, we do not try to be smart
1446-
* about it --- we just drop pages from the end of the rel's data.
1443+
* In corner cases where we are on the short end of a roundoff choice
1444+
* that we were formerly on the long end of, it's possible that we
1445+
* have to move down and compress our data too. In fact, even after
1446+
* pushing down the following rels, there might not be as much space
1447+
* as we computed for this rel above --- that would imply that some
1448+
* following rel(s) are also on the losing end of roundoff choices.
1449+
* We could handle this fairly by doing the per-rel compactions
1450+
* out-of-order, but that seems like way too much complexity to deal
1451+
* with a very infrequent corner case. Instead, we simply drop pages
1452+
* from the end of the current rel's data until it fits.
14471453
*/
14481454
if (newChunkIndex>oldChunkIndex)
14491455
{
@@ -1455,21 +1461,44 @@ compact_fsm_storage(void)
14551461
fsmrel->storedPages=newAllocPages;
14561462
curChunks=fsm_current_chunks(fsmrel);
14571463
}
1464+
/* is there enough space? */
14581465
if (fsmrel->nextPhysical!=NULL)
14591466
limitChunkIndex=fsmrel->nextPhysical->firstChunk;
14601467
else
14611468
limitChunkIndex=FreeSpaceMap->totalChunks;
14621469
if (newChunkIndex+curChunks>limitChunkIndex)
14631470
{
1464-
/* need to push down additional rels */
1465-
push_fsm_rels_after(fsmrel);
1466-
/* recheck for safety */
1471+
/* not enough space, push down following rels */
1472+
if (!did_push)
1473+
{
1474+
push_fsm_rels_after(fsmrel);
1475+
did_push= true;
1476+
}
1477+
/* now is there enough space? */
14671478
if (fsmrel->nextPhysical!=NULL)
14681479
limitChunkIndex=fsmrel->nextPhysical->firstChunk;
14691480
else
14701481
limitChunkIndex=FreeSpaceMap->totalChunks;
14711482
if (newChunkIndex+curChunks>limitChunkIndex)
1472-
elog(PANIC,"insufficient room in FSM");
1483+
{
1484+
/* uh-oh, forcibly cut the allocation to fit */
1485+
newAlloc=limitChunkIndex-newChunkIndex;
1486+
/*
1487+
* If newAlloc < 0 at this point, we are moving the rel's
1488+
* firstChunk into territory currently assigned to a later
1489+
* rel. This is okay so long as we do not copy any data.
1490+
* The rels will be back in nondecreasing firstChunk order
1491+
* at completion of the compaction pass.
1492+
*/
1493+
if (newAlloc<0)
1494+
newAlloc=0;
1495+
if (fsmrel->isIndex)
1496+
newAllocPages=newAlloc*INDEXCHUNKPAGES;
1497+
else
1498+
newAllocPages=newAlloc*CHUNKPAGES;
1499+
fsmrel->storedPages=newAllocPages;
1500+
curChunks=fsm_current_chunks(fsmrel);
1501+
}
14731502
}
14741503
memmove(newLocation,oldLocation,curChunks*CHUNKBYTES);
14751504
}
@@ -1504,6 +1533,7 @@ compact_fsm_storage(void)
15041533
memmove(newLocation,oldLocation,curChunks*CHUNKBYTES);
15051534
}
15061535
fsmrel->firstChunk=newChunkIndex;
1536+
nextChunkIndex+=newAlloc;
15071537
}
15081538
Assert(nextChunkIndex <=FreeSpaceMap->totalChunks);
15091539
FreeSpaceMap->usedChunks=nextChunkIndex;
@@ -1544,8 +1574,8 @@ push_fsm_rels_after(FSMRelation *afterRel)
15441574
oldChunkIndex=fsmrel->firstChunk;
15451575
if (newChunkIndex<oldChunkIndex)
15461576
{
1547-
/*trouble... */
1548-
elog(PANIC,"insufficient room in FSM");
1577+
/*we're pushing down, how can it move up? */
1578+
elog(PANIC,"inconsistent entry sizes in FSM");
15491579
}
15501580
elseif (newChunkIndex>oldChunkIndex)
15511581
{
@@ -1758,14 +1788,14 @@ fsm_current_chunks(FSMRelation *fsmrel)
17581788
{
17591789
intchunkCount;
17601790

1791+
/* Make sure storedPages==0 produces right answer */
1792+
if (fsmrel->storedPages <=0)
1793+
return0;
17611794
/* Convert page count to chunk count */
17621795
if (fsmrel->isIndex)
17631796
chunkCount= (fsmrel->storedPages-1) /INDEXCHUNKPAGES+1;
17641797
else
17651798
chunkCount= (fsmrel->storedPages-1) /CHUNKPAGES+1;
1766-
/* Make sure storedPages==0 produces right answer */
1767-
if (chunkCount<0)
1768-
chunkCount=0;
17691799
returnchunkCount;
17701800
}
17711801

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