diff options
Diffstat (limited to 'src/backend/access/nbtree/nbtscan.c')
| -rw-r--r-- | src/backend/access/nbtree/nbtscan.c | 29 |
1 files changed, 15 insertions, 14 deletions
diff --git a/src/backend/access/nbtree/nbtscan.c b/src/backend/access/nbtree/nbtscan.c index 37469365bcd..5d48895c1ad 100644 --- a/src/backend/access/nbtree/nbtscan.c +++ b/src/backend/access/nbtree/nbtscan.c @@ -8,22 +8,25 @@ * * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/access/nbtree/Attic/nbtscan.c,v 1.31 2000/04/12 17:14:49 momjian Exp $ + * $Header: /cvsroot/pgsql/src/backend/access/nbtree/Attic/nbtscan.c,v 1.32 2000/07/21 06:42:32 tgl Exp $ * * * NOTES * Because we can be doing an index scan on a relation while we update * it, we need to avoid missing data that moves around in the index. - * The routines and global variables in this file guarantee that all - * scans in the local address space stay correctly positioned. This - * is all we need to worry about, since write locking guarantees that - * no one else will be on the same page at the same time as we are. + * Insertions and page splits are no problem because _bt_restscan() + * can figure out where the current item moved to, but if a deletion + * happens at or before the current scan position, we'd better do + * something to stay in sync. + * + * The routines in this file handle the problem for deletions issued + * by the current backend. Currently, that's all we need, since + * deletions are only done by VACUUM and it gets an exclusive lock. * * The scheme is to manage a list of active scans in the current backend. - * Whenever we add or remove records from an index, or whenever we - * split a leaf page, we check the list of active scans to see if any - * has been affected. A scan is affected only if it is on the same - * relation, and the same page, as the update. + * Whenever we remove a record from an index, we check the list of active + * scans to see if any has been affected. A scan is affected only if it + * is on the same relation, and the same page, as the update. * *------------------------------------------------------------------------- */ @@ -111,7 +114,7 @@ _bt_dropscan(IndexScanDesc scan) /* * _bt_adjscans() -- adjust all scans in the scan list to compensate - * for a given deletion or insertion + * for a given deletion */ void _bt_adjscans(Relation rel, ItemPointer tid) @@ -153,7 +156,7 @@ _bt_scandel(IndexScanDesc scan, BlockNumber blkno, OffsetNumber offno) { page = BufferGetPage(buf); opaque = (BTPageOpaque) PageGetSpecialPointer(page); - start = P_RIGHTMOST(opaque) ? P_HIKEY : P_FIRSTKEY; + start = P_FIRSTDATAKEY(opaque); if (ItemPointerGetOffsetNumber(current) == start) ItemPointerSetInvalid(&(so->curHeapIptr)); else @@ -165,7 +168,6 @@ _bt_scandel(IndexScanDesc scan, BlockNumber blkno, OffsetNumber offno) */ LockBuffer(buf, BT_READ); _bt_step(scan, &buf, BackwardScanDirection); - so->btso_curbuf = buf; if (ItemPointerIsValid(current)) { Page pg = BufferGetPage(buf); @@ -183,10 +185,9 @@ _bt_scandel(IndexScanDesc scan, BlockNumber blkno, OffsetNumber offno) && ItemPointerGetBlockNumber(current) == blkno && ItemPointerGetOffsetNumber(current) >= offno) { - page = BufferGetPage(so->btso_mrkbuf); opaque = (BTPageOpaque) PageGetSpecialPointer(page); - start = P_RIGHTMOST(opaque) ? P_HIKEY : P_FIRSTKEY; + start = P_FIRSTDATAKEY(opaque); if (ItemPointerGetOffsetNumber(current) == start) ItemPointerSetInvalid(&(so->mrkHeapIptr)); |