Re: Bitmap index scans use of filters on available columns

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.
        regards, tom lane