Re: Sort time

I've applied the attached patch to current sources (7.4devel). It
eliminates palloc/pfree overhead in varstr_cmp() for short strings
(up to 1K as committed). I find that this reduces the sort time for
700,000 rows by about 10% on my HPUX box; might be better on machines
with better-optimized strcoll().

regards, tom lane

*** src/backend/utils/adt/varlena.c.orig Wed Sep 4 17:30:48 2002
--- src/backend/utils/adt/varlena.c Sun Nov 17 17:21:43 2002
***************
*** 736,771 ****
varstr_cmp(char *arg1, int len1, char *arg2, int len2)
{
int result;
- char *a1p,
- *a2p;

/*
* Unfortunately, there is no strncoll(), so in the non-C locale case
* we have to do some memory copying. This turns out to be
* significantly slower, so we optimize the case where LC_COLLATE is
! * C.
*/
if (!lc_collate_is_c())
{
! a1p = (char *) palloc(len1 + 1);
! a2p = (char *) palloc(len2 + 1);

memcpy(a1p, arg1, len1);
! *(a1p + len1) = '\0';
memcpy(a2p, arg2, len2);
! *(a2p + len2) = '\0';

result = strcoll(a1p, a2p);

! pfree(a1p);
! pfree(a2p);
}
else
{
! a1p = arg1;
! a2p = arg2;
!
! result = strncmp(a1p, a2p, Min(len1, len2));
if ((result == 0) && (len1 != len2))
result = (len1 < len2) ? -1 : 1;
}
--- 736,782 ----
varstr_cmp(char *arg1, int len1, char *arg2, int len2)
{
int result;

/*
* Unfortunately, there is no strncoll(), so in the non-C locale case
* we have to do some memory copying. This turns out to be
* significantly slower, so we optimize the case where LC_COLLATE is
! * C. We also try to optimize relatively-short strings by avoiding
! * palloc/pfree overhead.
*/
+ #define STACKBUFLEN 1024
+
if (!lc_collate_is_c())
{
! char a1buf[STACKBUFLEN];
! char a2buf[STACKBUFLEN];
! char *a1p,
! *a2p;
!
! if (len1 >= STACKBUFLEN)
! a1p = (char *) palloc(len1 + 1);
! else
! a1p = a1buf;
! if (len2 >= STACKBUFLEN)
! a2p = (char *) palloc(len2 + 1);
! else
! a2p = a2buf;

memcpy(a1p, arg1, len1);
! a1p[len1] = '\0';
memcpy(a2p, arg2, len2);
! a2p[len2] = '\0';

result = strcoll(a1p, a2p);

! if (len1 >= STACKBUFLEN)
! pfree(a1p);
! if (len2 >= STACKBUFLEN)
! pfree(a2p);
}
else
{
! result = strncmp(arg1, arg2, Min(len1, len2));
if ((result == 0) && (len1 != len2))
result = (len1 < len2) ? -1 : 1;
}