Re: btree_gist macaddr valgrind woes

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>
Cc: Andres Freund <andres(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: btree_gist macaddr valgrind woes
Date: 2014-05-16 19:36:29
Message-ID: 21448.1400268989@sss.pgh.pa.us
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Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> writes:
> ISTM the "correct" fix would be to define a gbtreekey12 data type and
> use that. That's not back-patchable though, and introducing a whole new
> type to save a few bytes is hardly worth it. What you did makes sense.

BTW, the *real* problem with all this stuff is that the gbtreekeyNN types
are declared as having int alignment, even though some of the opclasses
store double-aligned types in them. I imagine it's possible to provoke
bus errors on machines that are picky about alignment. The first column
of an index is safe enough because index tuples will be double-aligned
anyway, but it seems like there's a hazard for lower-order columns.
This is something we cannot fix compatibly :-(

regards, tom lane

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