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Fix obsolete nbtree README left link remarks.

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Oversight in commit 1bd4bc85, which made nbtree backwards scans operate
off of a copy of each page's left link as of the time of its call to
_bt_readpage.
This commit is contained in:
Peter Geoghegan
2025-01-10 15:42:17 -05:00
parent 3d0b4b1068
commit 5b14ec0a48
1 changed files with 3 additions and 3 deletions
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src/backend/access/nbtree/README
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@ -99,9 +99,9 @@ cannot miss any items it should have seen, nor accidentally return the same
item twice. The scan must remember the page's right-link at the time it item twice. The scan must remember the page's right-link at the time it
was scanned, since that is the page to move right to; if we move right to was scanned, since that is the page to move right to; if we move right to
the current right-link then we'd re-scan any items moved by a page split. the current right-link then we'd re-scan any items moved by a page split.
We don't similarly remember the left-link, since it's best to use the most We also remember the left-link, and follow it when the scan moves backwards
up-to-date left-link when trying to move left (see detailed move-left (though this requires extra handling to account for concurrent splits of
algorithm below). the left sibling; see detailed move-left algorithm below).
In most cases we release our lock and pin on a page before attempting In most cases we release our lock and pin on a page before attempting
to acquire pin and lock on the page we are moving to. In a few places to acquire pin and lock on the page we are moving to. In a few places