On Mon, Nov 20, 2023 at 5:54 AM Jeff Davis <pg...@j-davis.com> wrote:
>
> Attached are a bunch of tiny patches and some perf numbers based on
> simple test described here:
>
> https://www.postgresql.org/message-id/04c8592dbd694e4114a3ed87139a7a04e4363030.camel%40j-davis.com
I tried taking I/O out, like this, thinking the times would be less variable:
cat bench.sql
select 1 from generate_series(1,500000) x(x), lateral (SELECT
inc_ab(x)) a offset 10000000;
(with turbo off)
pgbench -n -T 30 -f bench.sql -M prepared
master:
latency average = 643.625 ms
0001-0005:
latency average = 607.354 ms
...about 5.5% less time, similar to what Jeff found.
I get a noticeable regression in 0002, though, and I think I see why:
guc_name_hash(const char *name)
{
- uint32 result = 0;
+ const unsigned char *bytes = (const unsigned char *)name;
+ int blen = strlen(name);
The strlen call required for hashbytes() is not free. The lack of
mixing in the (probably inlined after 0001) previous hash function can
remedied directly, as in the attached:
0001-0002 only:
latency average = 670.059 ms
0001-0002, plus revert hashbytes, add finalizer:
latency average = 656.810 ms
-#define SH_EQUAL(tb, a, b) (guc_name_compare(a, b) == 0)
+#define SH_EQUAL(tb, a, b) (strcmp(a, b) == 0)
Likewise, I suspect calling out to the C library is going to throw
away some of the gains that were won by not needing to downcase all
the time, but I haven't dug deeper.
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index b51d10dbc0..124b8fbe85 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1363,10 +1363,17 @@ guc_name_compare(const char *namea, const char *nameb)
static uint32
guc_name_hash(const char *name)
{
- const unsigned char *bytes = (const unsigned char *)name;
- int blen = strlen(name);
+ uint32 result = 0;
- return hash_bytes(bytes, blen);
+ while (*name)
+ {
+ char ch = *name++;
+
+ /* Merge into hash ... not very bright, but it needn't be */
+ result = pg_rotate_left32(result, 5);
+ result ^= (uint32) ch;
+ }
+ return murmurhash32(result);
}
/*
