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Second try at fixing no-room-to-move-down PANIC in compact_fsm_storage.

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Ward's report that it can still happen in RC2 forces me to realize that
this is not a can't-happen condition after all, and that the compaction
code had better cope rather than panicking.
This commit is contained in:
Tom Lane 2003-11-26 20:50:11 +00:00
parent 5392e73b6c
commit 9ea738827c
1 changed files with 47 additions and 17 deletions
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64
src/backend/storage/freespace/freespace.c
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@ -8,7 +8,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/freespace/freespace.c,v 1.24 2003/10/29 17:36:57 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/storage/freespace/freespace.c,v 1.25 2003/11/26 20:50:11 tgl Exp $
*
*
* NOTES:
@ -1394,6 +1394,7 @@ static void
compact_fsm_storage(void)
{
int nextChunkIndex = 0;
bool did_push = false;
FSMRelation *fsmrel;
for (fsmrel = FreeSpaceMap->firstRel;
@ -1419,16 +1420,15 @@ compact_fsm_storage(void)
newAllocPages = newAlloc * INDEXCHUNKPAGES;
else
newAllocPages = newAlloc * CHUNKPAGES;
newChunkIndex = nextChunkIndex;
nextChunkIndex += newAlloc;
/*
* Determine current size, current and new locations
*/
curChunks = fsm_current_chunks(fsmrel);
oldChunkIndex = fsmrel->firstChunk;
newLocation = FreeSpaceMap->arena + newChunkIndex * CHUNKBYTES;
oldLocation = FreeSpaceMap->arena + oldChunkIndex * CHUNKBYTES;
newChunkIndex = nextChunkIndex;
newLocation = FreeSpaceMap->arena + newChunkIndex * CHUNKBYTES;
/*
* It's possible that we have to move data down, not up, if the
@ -1440,10 +1440,16 @@ compact_fsm_storage(void)
* more than once, so pack everything against the end of the arena
* if so.
*
* In corner cases where roundoff has affected our allocation, it's
* possible that we have to move down and compress our data too.
* Since this case is extremely infrequent, we do not try to be smart
* about it --- we just drop pages from the end of the rel's data.
* In corner cases where we are on the short end of a roundoff choice
* that we were formerly on the long end of, it's possible that we
* have to move down and compress our data too. In fact, even after
* pushing down the following rels, there might not be as much space
* as we computed for this rel above --- that would imply that some
* following rel(s) are also on the losing end of roundoff choices.
* We could handle this fairly by doing the per-rel compactions
* out-of-order, but that seems like way too much complexity to deal
* with a very infrequent corner case. Instead, we simply drop pages
* from the end of the current rel's data until it fits.
*/
if (newChunkIndex > oldChunkIndex)
{
@ -1455,21 +1461,44 @@ compact_fsm_storage(void)
fsmrel->storedPages = newAllocPages;
curChunks = fsm_current_chunks(fsmrel);
}
/* is there enough space? */
if (fsmrel->nextPhysical != NULL)
limitChunkIndex = fsmrel->nextPhysical->firstChunk;
else
limitChunkIndex = FreeSpaceMap->totalChunks;
if (newChunkIndex + curChunks > limitChunkIndex)
{
/* need to push down additional rels */
push_fsm_rels_after(fsmrel);
/* recheck for safety */
/* not enough space, push down following rels */
if (!did_push)
{
push_fsm_rels_after(fsmrel);
did_push = true;
}
/* now is there enough space? */
if (fsmrel->nextPhysical != NULL)
limitChunkIndex = fsmrel->nextPhysical->firstChunk;
else
limitChunkIndex = FreeSpaceMap->totalChunks;
if (newChunkIndex + curChunks > limitChunkIndex)
elog(PANIC, "insufficient room in FSM");
{
/* uh-oh, forcibly cut the allocation to fit */
newAlloc = limitChunkIndex - newChunkIndex;
/*
* If newAlloc < 0 at this point, we are moving the rel's
* firstChunk into territory currently assigned to a later
* rel. This is okay so long as we do not copy any data.
* The rels will be back in nondecreasing firstChunk order
* at completion of the compaction pass.
*/
if (newAlloc < 0)
newAlloc = 0;
if (fsmrel->isIndex)
newAllocPages = newAlloc * INDEXCHUNKPAGES;
else
newAllocPages = newAlloc * CHUNKPAGES;
fsmrel->storedPages = newAllocPages;
curChunks = fsm_current_chunks(fsmrel);
}
}
memmove(newLocation, oldLocation, curChunks * CHUNKBYTES);
}
@ -1504,6 +1533,7 @@ compact_fsm_storage(void)
memmove(newLocation, oldLocation, curChunks * CHUNKBYTES);
}
fsmrel->firstChunk = newChunkIndex;
nextChunkIndex += newAlloc;
}
Assert(nextChunkIndex <= FreeSpaceMap->totalChunks);
FreeSpaceMap->usedChunks = nextChunkIndex;
@ -1544,8 +1574,8 @@ push_fsm_rels_after(FSMRelation *afterRel)
oldChunkIndex = fsmrel->firstChunk;
if (newChunkIndex < oldChunkIndex)
{
/* trouble... */
elog(PANIC, "insufficient room in FSM");
/* we're pushing down, how can it move up? */
elog(PANIC, "inconsistent entry sizes in FSM");
}
else if (newChunkIndex > oldChunkIndex)
{
@ -1758,14 +1788,14 @@ fsm_current_chunks(FSMRelation *fsmrel)
{
int chunkCount;
/* Make sure storedPages==0 produces right answer */
if (fsmrel->storedPages <= 0)
return 0;
/* Convert page count to chunk count */
if (fsmrel->isIndex)
chunkCount = (fsmrel->storedPages - 1) / INDEXCHUNKPAGES + 1;
else
chunkCount = (fsmrel->storedPages - 1) / CHUNKPAGES + 1;
/* Make sure storedPages==0 produces right answer */
if (chunkCount < 0)
chunkCount = 0;
return chunkCount;
}