From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Peter Geoghegan <pg(at)heroku(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Stephen Frost <sfrost(at)snowman(dot)net> |
Subject: | Re: Performance optimization of btree binary search |
Date: | 2013-12-04 23:56:30 |
Message-ID: | 28844.1386201390@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Hmm. And yet, there's this:
> * When a type narrower than Datum is stored in a Datum, we place it in the
> * low-order bits and are careful that the DatumGetXXX macro for it discards
> * the unused high-order bits (as opposed to, say, assuming they are zero).
> * This is needed to support old-style user-defined functions, since depending
> * on architecture and compiler, the return value of a function returning char
> * or short may contain garbage when called as if it returned Datum.
> And record_image_eq does a rather elaborate dance around here, calling
> the appropriate GET_x_BYTES macro depending on the type-width. If we
> can really count on the high-order bits to be zero, that's all
> completely unnecessary tomfoolery.
Yeah, that's another thing we could simplify if we fixed this problem
at the source. I think these decisions date from a time when we still
cared about the speed of fmgr_oldstyle.
regards, tom lane
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