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refs/reftable: precompute prefix length

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We're recomputing the prefix length on every iteration of the ref
iterator. Precompute it for another speedup when iterating over 1
million refs:

    Benchmark 1: show-ref: single matching ref (revision = HEAD~)
      Time (mean ± σ):     100.3 ms ±   3.7 ms    [User: 97.3 ms, System: 2.8 ms]
      Range (min … max):    97.5 ms … 139.7 ms    1000 runs

    Benchmark 2: show-ref: single matching ref (revision = HEAD)
      Time (mean ± σ):      95.8 ms ±   3.4 ms    [User: 92.9 ms, System: 2.8 ms]
      Range (min … max):    93.0 ms … 121.9 ms    1000 runs

    Summary
      show-ref: single matching ref (revision = HEAD) ran
        1.05 ± 0.05 times faster than show-ref: single matching ref (revision = HEAD~)

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Patrick Steinhardt 2024-03-04 11:49:40 +01:00 committed by Junio C Hamano
parent f1bf54aee3
commit 43f70eaea0
1 changed files with 4 additions and 2 deletions
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6
refs/reftable-backend.c
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@ -346,6 +346,7 @@ struct reftable_ref_iterator {
struct object_id oid;
const char *prefix;
size_t prefix_len;
unsigned int flags;
int err;
};
@ -371,8 +372,8 @@ static int reftable_ref_iterator_advance(struct ref_iterator *ref_iterator)
if (!starts_with(iter->ref.refname, "refs/"))
continue;
if (iter->prefix &&
strncmp(iter->prefix, iter->ref.refname, strlen(iter->prefix))) {
if (iter->prefix_len &&
strncmp(iter->prefix, iter->ref.refname, iter->prefix_len)) {
iter->err = 1;
break;
}
@ -481,6 +482,7 @@ static struct reftable_ref_iterator *ref_iterator_for_stack(struct reftable_ref_
iter = xcalloc(1, sizeof(*iter));
base_ref_iterator_init(&iter->base, &reftable_ref_iterator_vtable, 1);
iter->prefix = prefix;
iter->prefix_len = prefix ? strlen(prefix) : 0;
iter->base.oid = &iter->oid;
iter->flags = flags;
iter->refs = refs;