diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/access/nbtree/nbtsearch.c | 27 |
1 files changed, 8 insertions, 19 deletions
diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c index 8946649db6e..be61b3868f4 100644 --- a/src/backend/access/nbtree/nbtsearch.c +++ b/src/backend/access/nbtree/nbtsearch.c @@ -2036,8 +2036,8 @@ _bt_steppage(IndexScanDesc scan, ScanDirection dir) * _bt_readnextpage() -- Read next page containing valid data for scan * * On success exit, so->currPos is updated to contain data from the next - * interesting page. Caller is responsible to release lock and pin on - * buffer on success. We return true to indicate success. + * interesting page, and we return true. Caller must release the lock (and + * maybe the pin) on the buffer on success exit. * * If there are no more matching records in the given direction, we drop all * locks and pins, set so->currPos.buf to InvalidBuffer, and return false. @@ -2127,18 +2127,9 @@ _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno, ScanDirection dir) * * It might be possible to rearrange this code to have less overhead * in pinning and locking, but that would require capturing the left - * pointer when the page is initially read, and using it here, along - * with big changes to _bt_walk_left() and the code below. It is not - * clear whether this would be a win, since if the page immediately to - * the left splits after we read this page and before we step left, we - * would need to visit more pages than with the current code. - * - * Note that if we change the code so that we drop the pin for a scan - * which uses a non-MVCC snapshot, we will need to modify the code for - * walking left, to allow for the possibility that a referenced page - * has been deleted. As long as the buffer is pinned or the snapshot - * is MVCC the page cannot move past the half-dead state to fully - * deleted. + * sibling block number when the page is initially read, and then + * optimistically starting there (rather than pinning the page twice). + * It is not clear that this would be worth the complexity. */ if (BTScanPosIsPinned(so->currPos)) _bt_lockbuf(rel, so->currPos.buf, BT_READ); @@ -2243,9 +2234,8 @@ _bt_parallel_readpage(IndexScanDesc scan, BlockNumber blkno, ScanDirection dir) * Returns InvalidBuffer if there is no page to the left (no lock is held * in that case). * - * When working on a non-leaf level, it is possible for the returned page - * to be half-dead; the caller should check that condition and step left - * again if it's important. + * It is possible for the returned leaf page to be half-dead; caller must + * check that condition and step left again when required. */ static Buffer _bt_walk_left(Relation rel, Buffer buf) @@ -2288,8 +2278,7 @@ _bt_walk_left(Relation rel, Buffer buf) * anymore, not that its left sibling got split more than four times. * * Note that it is correct to test P_ISDELETED not P_IGNORE here, - * because half-dead pages are still in the sibling chain. Caller - * must reject half-dead pages if wanted. + * because half-dead pages are still in the sibling chain. */ tries = 0; for (;;) |