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Speed up uuid_out() by not relying on a StringInfo

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Since the size of the string representation of an uuid is fixed, there
is no benefit in using a StringInfo.  This commit simplifies uuid_oud()
to not rely on a StringInfo, where avoiding the overhead of the string
manipulation makes the function substantially faster.

A COPY TO on a relation with one UUID attribute can show up to a 40%
speedup when the bottleneck is the COPY computation with uuid_out()
showing up at the top of the profiles (numbered measure here, Laurenz
has mentioned something closer to 20% faster runtimes), for example when
the data is fully in shared buffers or the OS cache.

Author: Laurenz Albe
Reviewed-by: Andres Freund, Michael Paquier
Description: https://postgr.es/m/679d5455cbbb0af667ccb753da51a475bae1eaed.camel@cybertec.at
This commit is contained in:
Michael Paquier 2024-02-22 10:02:55 +09:00
parent 943f7ae1c8
commit 011d60c435
1 changed files with 10 additions and 6 deletions
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16
src/backend/utils/adt/uuid.c
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@ -53,10 +53,13 @@ uuid_out(PG_FUNCTION_ARGS)
{
pg_uuid_t *uuid = PG_GETARG_UUID_P(0);
static const char hex_chars[] = "0123456789abcdef";
StringInfoData buf;
char *buf,
*p;
int i;
initStringInfo(&buf);
/* counts for the four hyphens and the zero-terminator */
buf = palloc(2 * UUID_LEN + 5);
p = buf;
for (i = 0; i < UUID_LEN; i++)
{
int hi;
@ -68,16 +71,17 @@ uuid_out(PG_FUNCTION_ARGS)
* ("-"). Therefore, add the hyphens at the appropriate places here.
*/
if (i == 4 || i == 6 || i == 8 || i == 10)
appendStringInfoChar(&buf, '-');
*p++ = '-';
hi = uuid->data[i] >> 4;
lo = uuid->data[i] & 0x0F;
appendStringInfoChar(&buf, hex_chars[hi]);
appendStringInfoChar(&buf, hex_chars[lo]);
*p++ = hex_chars[hi];
*p++ = hex_chars[lo];
}
*p = '\0';
PG_RETURN_CSTRING(buf.data);
PG_RETURN_CSTRING(buf);
}
/*