reftable/record: reuse refname when copying

Do the same optimization as in the preceding commit, but this time for
`reftable_record_copy()`. While not as noticeable, it still results in a
small speedup when iterating over 1 million refs:

  Benchmark 1: show-ref: single matching ref (revision = HEAD~)
    Time (mean ± σ):     114.0 ms ±   3.8 ms    [User: 111.1 ms, System: 2.7 ms]
    Range (min … max):   110.9 ms … 144.3 ms    1000 runs

  Benchmark 2: show-ref: single matching ref (revision = HEAD)
    Time (mean ± σ):     112.5 ms ±   3.7 ms    [User: 109.5 ms, System: 2.8 ms]
    Range (min … max):   109.2 ms … 140.7 ms    1000 runs

  Summary
    show-ref: single matching ref (revision = HEAD) ran
      1.01 ± 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>

diff --git a/reftable/record.c b/reftable/record.c
index 2b52e47c30ca82b96b1e881a2d54b42d67b37d8f..12a44f70e55c1458b73cec819ad9cb930a2d5bd0 100644 (file)
--- a/reftable/record.c
+++ b/reftable/record.c
@@ -205,14 +205,26 @@ static void reftable_ref_record_copy_from(void *rec, const void *src_rec,
 {
        struct reftable_ref_record *ref = rec;
        const struct reftable_ref_record *src = src_rec;
+       char *refname = NULL;
+       size_t refname_cap = 0;
+
        assert(hash_size > 0);
 
-       /* This is simple and correct, but we could probably reuse the hash
-        * fields. */
+       SWAP(refname, ref->refname);
+       SWAP(refname_cap, ref->refname_cap);
        reftable_ref_record_release(ref);
+       SWAP(ref->refname, refname);
+       SWAP(ref->refname_cap, refname_cap);
+
        if (src->refname) {
-               ref->refname = xstrdup(src->refname);
+               size_t refname_len = strlen(src->refname);
+
+               REFTABLE_ALLOC_GROW(ref->refname, refname_len + 1,
+                                   ref->refname_cap);
+               memcpy(ref->refname, src->refname, refname_len);
+               ref->refname[refname_len] = 0;
        }
+
        ref->update_index = src->update_index;
        ref->value_type = src->value_type;
        switch (src->value_type) {