diff options
Diffstat (limited to 'src/backend/access/heap/vacuumlazy.c')
| -rw-r--r-- | src/backend/access/heap/vacuumlazy.c | 36 |
1 files changed, 31 insertions, 5 deletions
diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c index 7f60d688686..53c72c14c3d 100644 --- a/src/backend/access/heap/vacuumlazy.c +++ b/src/backend/access/heap/vacuumlazy.c @@ -860,6 +860,8 @@ lazy_scan_heap(Relation onerel, int options, LVRelStats *vacrelstats, if (PageIsNew(page)) { + bool still_new; + /* * All-zeroes pages can be left over if either a backend extends * the relation by a single page, but crashes before the newly @@ -877,21 +879,45 @@ lazy_scan_heap(Relation onerel, int options, LVRelStats *vacrelstats, * promoted standby. The harm of repeated checking ought to * normally not be too bad - the space usually should be used at * some point, otherwise there wouldn't be any regular vacuums. + * + * We have to be careful here because we could be looking at a + * page that someone has just added to the relation and the + * extending backend might not yet have been able to lock the page + * (see RelationGetBufferForTuple), which is problematic because + * of cross-checks that new pages are actually new. If we add this + * page to the FSM, this page could be reused, and such + * crosschecks could fail. To protect against that, release the + * buffer lock, grab the relation extension lock momentarily, and + * re-lock the buffer. If the page is still empty and not in the + * FSM by then, it must be left over from a from a crashed + * backend, and we can record the free space. + * + * Note: the comparable code in vacuum.c need not worry because + * it's got an exclusive lock on the whole relation. */ - empty_pages++; + LockBuffer(buf, BUFFER_LOCK_UNLOCK); + LockRelationForExtension(onerel, ExclusiveLock); + UnlockRelationForExtension(onerel, ExclusiveLock); + LockBufferForCleanup(buf); /* * Perform checking of FSM after releasing lock, the fsm is * approximate, after all. */ + still_new = PageIsNew(page); UnlockReleaseBuffer(buf); - if (GetRecordedFreeSpace(onerel, blkno) == 0) + if (still_new) { - Size freespace; + empty_pages++; + + if (GetRecordedFreeSpace(onerel, blkno) == 0) + { + Size freespace; - freespace = BufferGetPageSize(buf) - SizeOfPageHeaderData; - RecordPageWithFreeSpace(onerel, blkno, freespace); + freespace = BufferGetPageSize(buf) - SizeOfPageHeaderData; + RecordPageWithFreeSpace(onerel, blkno, freespace); + } } continue; } |