[PATCH v2 7/8] reftable/merged: really reuse buffers to compute record keys

From: Patrick Steinhardt <ps@pks.im>
Date: Dec 28, 2023, 06:28 UTC
Message-ID: <6313f8affdc136b183c1bd411d481efe5c676aee.1703743174.git.ps@pks.im>
In-Reply-To: <cover.1703743174.git.ps@pks.im>

In 829231dc20 (reftable/merged: reuse buffer to compute record keys, 2023-12-11), we have refactored the merged iterator to reuse a set of buffers that it would otherwise have to reallocate on every single iteration. Unfortunately, there was a brown-paper-bag-style bug here as we continue to release these buffers after the iteration, and thus we have essentially gained nothing.

Fix this performance issue by not releasing those buffers on iteration anymore, where we instead rely on `merged_iter_close()` to release the buffers for us.

Using `git show-ref --quiet` in a repository with ~350k refs this leads to a significant drop in allocations. Before:

    HEAP SUMMARY:
        in use at exit: 21,163 bytes in 193 blocks
      total heap usage: 1,410,148 allocs, 1,409,955 frees, 61,976,068 bytes allocated

After:

    HEAP SUMMARY:
        in use at exit: 21,163 bytes in 193 blocks
      total heap usage: 708,058 allocs, 707,865 frees, 36,783,255 bytes allocated

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 reftable/merged.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/reftable/merged.c b/reftable/merged.c
index 556bb5c556..a28bb99aaf 100644
--- a/reftable/merged.c
+++ b/reftable/merged.c
@@ -128,8 +128,6 @@ static int merged_iter_next_entry(struct merged_iter *mi,
 
 done:
 	reftable_record_release(&entry.rec);
-	strbuf_release(&mi->entry_key);
-	strbuf_release(&mi->key);
 	return err;
 }

-- 
2.43.GIT