Hello,
Since commit cdf91edb (2012), nodeIndexonlyscan.c says:
/*
* Predicate locks for index-only scans must be
acquired at the page
* level when the heap is not accessed, since
tuple-level predicate
* locks need the tuple's xmin value. If we had to
visit the tuple
* anyway, then we already have the tuple-level lock
and can skip the
* page lock.
*/
if (tuple == NULL)
PredicateLockPage(scandesc->heapRelation,
ItemPointerGetBlockNumber(tid),
estate->es_snapshot);
The first sentence of that comment is no longer true as of commit
c01262a8 (2013). As for whether it's necessary to predicate-lock the
whole eheap page (rather than the heap tuple) anyway because of HOT
update chains, I don't know, so I'm not sure what wording to propose
instead.
--
Thomas Munro
http://www.enterprisedb.com
