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Diffstat (limited to 'src/backend/access/gin/README')
| -rw-r--r-- | src/backend/access/gin/README | 15 |
1 files changed, 4 insertions, 11 deletions
diff --git a/src/backend/access/gin/README b/src/backend/access/gin/README index cc434b1feb7..421b5b26d5b 100644 --- a/src/backend/access/gin/README +++ b/src/backend/access/gin/README @@ -314,17 +314,10 @@ deleted. The previous paragraph's reasoning only applies to searches, and only to posting trees. To protect from inserters following a downlink to a deleted page, vacuum simply locks out all concurrent insertions to the posting tree, -by holding a super-exclusive lock on the parent page of subtree with deletable -pages. Inserters hold a pin on the root page, but searches do not, so while -new searches cannot begin while root page is locked, any already-in-progress -scans can continue concurrently with vacuum in corresponding subtree of -posting tree. To exclude interference with readers vacuum takes exclusive -locks in a depth-first scan in left-to-right order of page tuples. Leftmost -page is never deleted. Thus before deleting any page we obtain exclusive -lock on any left page, effectively excluding deadlock with any reader, despite -taking parent lock before current and left lock after current. We take left -lock not for a concurrency reasons, but rather in need to mark page dirty. -In the entry tree, we never delete pages. +by holding a super-exclusive lock on the posting tree root. Inserters hold a +pin on the root page, but searches do not, so while new searches cannot begin +while root page is locked, any already-in-progress scans can continue +concurrently with vacuum. In the entry tree, we never delete pages. (This is quite different from the mechanism the btree indexam uses to make page-deletions safe; it stamps the deleted pages with an XID and keeps the |