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[6/7] reftable/record: don't try to reallocate ref record name

Message ID 41dff8731c308c6d72ebd0066be8963bda725ea2.1706782841.git.ps@pks.im (mailing list archive)
State Superseded
Headers show
Series reftable: improve ref iteration performance | expand

Commit Message

Patrick Steinhardt Feb. 1, 2024, 10:25 a.m. UTC 
When decoding reftable ref records we first release the pointer to the
record passed to us and then use realloc(3P) to allocate the refname
array. This is a bit misleading though as we know at that point that the
refname will always be `NULL`, so we would always end up allocating a
new char array anyway.

Refactor the code to use `REFTABLE_ALLOC_ARRAY()` instead. As the
following benchmark demonstrates this is a tiny bit more efficient. But
the bigger selling point really is the gained clarity.

  Benchmark 1: show-ref: single matching ref (revision = HEAD~)
    Time (mean ± σ):     150.1 ms ±   4.1 ms    [User: 146.6 ms, System: 3.3 ms]
    Range (min … max):   144.5 ms … 180.5 ms    1000 runs

  Benchmark 2: show-ref: single matching ref (revision = HEAD)
    Time (mean ± σ):     148.9 ms ±   4.5 ms    [User: 145.2 ms, System: 3.4 ms]
    Range (min … max):   143.0 ms … 185.4 ms    1000 runs

  Summary
    show-ref: single matching ref (revision = HEAD) ran
      1.01 ± 0.04 times faster than show-ref: single matching ref (revision = HEAD~)

Ideally, we should try and reuse the memory of the old record instead of
first freeing and then immediately reallocating it. This requires some
more surgery though and is thus left for a future iteration.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/record.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
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Patch

diff --git a/reftable/record.c b/reftable/record.c
index f1b6a5eac9..6465a7b8f4 100644
--- a/reftable/record.c
+++ b/reftable/record.c
@@ -377,10 +377,11 @@  static int reftable_ref_record_decode(void *rec, struct strbuf key,
 
 	assert(hash_size > 0);
 
-	r->refname = reftable_realloc(r->refname, key.len + 1);
+	r->refname = reftable_malloc(key.len + 1);
 	memcpy(r->refname, key.buf, key.len);
-	r->update_index = update_index;
 	r->refname[key.len] = 0;
+
+	r->update_index = update_index;
 	r->value_type = val_type;
 	switch (val_type) {
 	case REFTABLE_REF_VAL1: