On 13.01.2011 16:51, Kevin Grittner wrote:
Right.  As each tuple is read we need to ensure that there is a
predicate lock to cover it.  Since finer-grained locks can be
combined into coarser-grained locks we need to start with the fine
grained and move toward checking the coarser grains, to avoid
missing a lock during promotion.  So for each tuple we calculate a
hash, find a partition, lock it, and lookup the tuple as a lock
target.  When that's not found we do the same thing for the page.
When that's not found we do the same thing for the relation.

But we acquired a relation lock up front, when we determined that
this would be a heap scan, so we could short-circuit this whole
thing if within the heapgettup_pagemode function we could determine
that this was a scan of the whole relation.

That sounds simple enough. Add a boolean field to HeapScanDesc, "rs_relpredicatelocked", and set it when you acquire the relation lock.

  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com

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