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Add some comments to tinterval_cmp_internal pointing out its severe

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implementation deficiencies.  Per discussion of bug #5592, we're not
going to change it, but these things should be documented so that if
anyone ever reimplements type tinterval, they will be more careful.
This commit is contained in:
Tom Lane
2010-08-03 16:31:02 +00:00
parent 31b6fc06d8
commit 72405b066b
1 changed files with 17 additions and 4 deletions
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21
src/backend/utils/adt/nabstime.c
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@ -10,7 +10,7 @@
* *
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/adt/nabstime.c,v 1.164 2010/02/26 02:01:09 momjian Exp $ * $PostgreSQL: pgsql/src/backend/utils/adt/nabstime.c,v 1.165 2010/08/03 16:31:02 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -1155,9 +1155,22 @@ tintervalsame(PG_FUNCTION_ARGS)
/* /*
* tinterval comparison routines * tinterval comparison routines
* *
* Note: comparison is based on the lengths of the tintervals, not on * Note: comparison is based only on the lengths of the tintervals, not on
* endpoint value. This is pretty bogus, but since it's only a legacy * endpoint values (as long as they're not INVALID). This is pretty bogus,
* datatype I'm not going to propose changing it. * but since it's only a legacy datatype, we're not going to change it.
*
* Some other bogus things that won't be changed for compatibility reasons:
* 1. The interval length computations overflow at 2^31 seconds, causing
* intervals longer than that to sort oddly compared to those shorter.
* 2. infinity and minus infinity (NOEND_ABSTIME and NOSTART_ABSTIME) are
* just ordinary integers. Since this code doesn't handle them specially,
* it's possible for [a b] to be considered longer than [c infinity] for
* finite abstimes a, b, c. In combination with the previous point, the
* interval [-infinity infinity] is treated as being shorter than many finite
* intervals :-(
*
* If tinterval is ever reimplemented atop timestamp, it'd be good to give
* some consideration to avoiding these problems.
*/ */
static int static int
tinterval_cmp_internal(TimeInterval a, TimeInterval b) tinterval_cmp_internal(TimeInterval a, TimeInterval b)