diff options
| -rw-r--r-- | src/backend/access/nbtree/README | 10 | ||||
| -rw-r--r-- | src/backend/access/nbtree/nbtpage.c | 2 |
2 files changed, 7 insertions, 5 deletions
diff --git a/src/backend/access/nbtree/README b/src/backend/access/nbtree/README index 9fe84e320e2..101ed38a232 100644 --- a/src/backend/access/nbtree/README +++ b/src/backend/access/nbtree/README @@ -261,13 +261,15 @@ we need to be sure we don't miss or re-scan any items. A deleted page can only be reclaimed once there is no scan or search that has a reference to it; until then, it must stay in place with its -right-link undisturbed. We implement this by waiting until all -transactions that were running at the time of deletion are dead; which is +right-link undisturbed. We implement this by waiting until all active +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 the oldest open transaction. (NOTE: VACUUM FULL can reclaim -such pages immediately.) +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. +(NOTE: VACUUM FULL can reclaim such pages immediately.) 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 diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c index ad458a9fe45..9fa29776dfb 100644 --- a/src/backend/access/nbtree/nbtpage.c +++ b/src/backend/access/nbtree/nbtpage.c @@ -639,7 +639,7 @@ _bt_page_recyclable(Page page) */ opaque = (BTPageOpaque) PageGetSpecialPointer(page); if (P_ISDELETED(opaque) && - TransactionIdPrecedesOrEquals(opaque->btpo.xact, RecentXmin)) + TransactionIdPrecedes(opaque->btpo.xact, RecentGlobalXmin)) return true; return false; } |