Re: Hash Indexes

<p dir="ltr">On 30-Sep-2016 6:24 AM, "Robert Haas" <<a
href="mailto:robertmhaas@gmail.com">robertmhaas@gmail.com</a>>wrote:<br /> ><br /> > On Thu, Sep 29, 2016 at
8:29PM, Andres Freund <<a href="mailto:andres@anarazel.de">andres@anarazel.de</a>> wrote:<br /> > > On
September29, 2016 5:28:00 PM PDT, Robert Haas <<a href="mailto:robertmhaas@gmail.com">robertmhaas@gmail.com</a>>
wrote:<br/> > >>On Thu, Sep 29, 2016 at 8:16 PM, Andres Freund <<a
href="mailto:andres@anarazel.de">andres@anarazel.de</a>><br/> > >>wrote:<br /> > >>>> Well,
I,for one, find it frustrating.  It seems pretty unhelpful to<br /> > >>>> bring this up only after the
codehas already been written.<br /> > >>><br /> > >>> I brought this up in person at pgcon
too.<br/> > >><br /> > >>To whom?  In what context?<br /> > ><br /> > > Amit, over
dinner.<br/> ><br /> > OK, well, I can't really comment on that, then, except to say that if<br /> > you
waitedthree months to follow up on the mailing list, you probably<br /> > can't blame Amit if he thought that it was
moreof a casual suggestion<br /> > than a serious objection.  Maybe it was?  I don't know.<br /> ><p
dir="ltr">Bothof them have talked about hash indexes with me offline. Peter mentioned that it would be better to
improvebtree rather than hash indexes. IIRC, Andres asked me mainly about what use cases I have in mind for hash
indexesand then we do have some further discussion on the same thing where he was not convinced that there is any big
usecase for hash indexes even though there may be some cases. In that discussion, as he is saying and I don't doubt
him,he would have told me the alternative, but it was not apparent to me that he is expecting some sort of
comparison.<pdir="ltr">What I got from both the discussions was a friendly gesture that it might be a better use of my
time,if I work on some other problem.  I really respect suggestions from both of them, but it was no where clear to me
thatany one of  them is expecting any comparison of other approach.<p dir="ltr">Considering,  I have missed the real
intentionof their suggestions, I think such a serious objection on any work should be discussed on list.  To answer the
actualobjection, I have already mentioned upthread that we can deduce from the current tests done by Jesper and Mithun
thatthere are some cases where hash index will be better than hash-over-btree (tests done over integer columns).  I
thinkany discussion on whether we should consider not to improve current hash indexes is only meaningful if some one
hasa  code which can prove both theoretically and practically that it is better than hash indexes for all usages.<p
dir="ltr">Note- excuse me for formatting of this email as I am on travel and using my phone.<p dir="ltr">With Regards,
<br/> Amit Kapila.<br />