Simon Riggs <simon@2ndquadrant.com> writes: > On 4 November 2015 at 16:14, Tom Lane <tgl@sss.pgh.pa.us> wrote: >> You're missing my point: that is possible in an indexscan, but *not* in a >> bitmap indexscan, because the index AM APIs are totally different in the >> two cases. In a bitmap scan, nothing more than a TID bitmap is ever >> returned out to anyplace that could execute arbitrary expressions.
> Still misunderstanding each other... sorry about that
> If a btree can Filter y like that on an IndexScan, then it can also apply > that Filter on y when it is looking through rows before it adds them to the > bitmap.
btree applies no such filter in either case. "Filter" conditions are applied outside the index AM --- and yes, I will resist any proposal to relocate that responsibility.
I don't think anyone has argued that point, yet, we just don't have enough info to agree yet.
As Jeff said in his OP, "Is there a fundamental reason the filter on y is not being applied to
the index scan, rather than the heap scan?", which still stands.
Why would you resist? And/Or Why is that important?
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Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
