From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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: | 2013-12-05 00:45:56 |
Message-ID: | CA+TgmoaY_cGKnxj5fyZj7kvfc+NA+9zPoab7NUCoSmkjGCee4A@mail.gmail.com |
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Lists: | pgsql-hackers |
On Wed, Dec 4, 2013 at 6:56 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> 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.
Sure, let's whack that thing with a crowbar.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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