diff options
Diffstat (limited to 'src/backend/access/nbtree/README')
| -rw-r--r-- | src/backend/access/nbtree/README | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/src/backend/access/nbtree/README b/src/backend/access/nbtree/README index abce31a5a96..781a8f1932d 100644 --- a/src/backend/access/nbtree/README +++ b/src/backend/access/nbtree/README @@ -342,9 +342,9 @@ snapshots and registered snapshots as of the deletion are gone; which is overly strong, but is simple to implement within Postgres. When marked dead, a deleted page is labeled with the next-transaction counter value. VACUUM can reclaim the page for re-use when this transaction number is -older than RecentGlobalXmin. As collateral damage, this implementation -also waits for running XIDs with no snapshots and for snapshots taken -until the next transaction to allocate an XID commits. +guaranteed to be "visible to everyone". As collateral damage, this +implementation also waits for running XIDs with no snapshots and for +snapshots taken until the next transaction to allocate an XID commits. Reclaiming a page doesn't actually change its state on disk --- we simply record it in the shared-memory free space map, from which it will be @@ -411,8 +411,8 @@ page and also the correct place to hold the current value. We can avoid the cost of walking down the tree in such common cases. The optimization works on the assumption that there can only be one -non-ignorable leaf rightmost page, and so even a RecentGlobalXmin style -interlock isn't required. We cannot fail to detect that our hint was +non-ignorable leaf rightmost page, and so not even a visible-to-everyone +style interlock required. We cannot fail to detect that our hint was invalidated, because there can only be one such page in the B-Tree at any time. It's possible that the page will be deleted and recycled without a backend's cached page also being detected as invalidated, but |