reftable/record: convert old and new object IDs to arrays

In 7af607c58d (reftable/record: store "val1" hashes as static arrays,
2024-01-03) and b31e3cc620 (reftable/record: store "val2" hashes as
static arrays, 2024-01-03) we have converted ref records to store their
object IDs in a static array. Convert log records to do the same so that
their old and new object IDs are arrays, too.

This change results in two allocations less per log record that we're
iterating over. Before:

    HEAP SUMMARY:
        in use at exit: 13,473 bytes in 122 blocks
      total heap usage: 8,068,495 allocs, 8,068,373 frees, 401,011,862 bytes allocated

After:

    HEAP SUMMARY:
        in use at exit: 13,473 bytes in 122 blocks
      total heap usage: 6,068,489 allocs, 6,068,367 frees, 361,011,822 bytes allocated

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 9 insertions, 30 deletions

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index f04be942ac..2de57c047a 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -171,23 +171,6 @@ static int should_write_log(struct ref_store *refs, const char *refname)
 	}
 }
 
-static void clear_reftable_log_record(struct reftable_log_record *log)
-{
-	switch (log->value_type) {
-	case REFTABLE_LOG_UPDATE:
-		/*
-		 * When we write log records, the hashes are owned by the
-		 * caller and thus shouldn't be free'd.
-		 */
-		log->value.update.old_hash = NULL;
-		log->value.update.new_hash = NULL;
-		break;
-	case REFTABLE_LOG_DELETION:
-		break;
-	}
-	reftable_log_record_release(log);
-}
-
 static void fill_reftable_log_record(struct reftable_log_record *log)
 {
 	const char *info = git_committer_info(0);
@@ -1102,8 +1085,8 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 			fill_reftable_log_record(log);
 			log->update_index = ts;
 			log->refname = xstrdup(u->refname);
-			log->value.update.new_hash = u->new_oid.hash;
-			log->value.update.old_hash = tx_update->current_oid.hash;
+			memcpy(log->value.update.new_hash, u->new_oid.hash, GIT_MAX_RAWSZ);
+			memcpy(log->value.update.old_hash, tx_update->current_oid.hash, GIT_MAX_RAWSZ);
 			log->value.update.message =
 				xstrndup(u->msg, arg->refs->write_options.block_size / 2);
 		}
@@ -1158,7 +1141,7 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 done:
 	assert(ret != REFTABLE_API_ERROR);
 	for (i = 0; i < logs_nr; i++)
-		clear_reftable_log_record(&logs[i]);
+		reftable_log_record_release(&logs[i]);
 	free(logs);
 	return ret;
 }
@@ -1275,13 +1258,13 @@ static int write_create_symref_table(struct reftable_writer *writer, void *cb_da
 	log.update_index = ts;
 	log.value.update.message = xstrndup(create->logmsg,
 					    create->refs->write_options.block_size / 2);
-	log.value.update.new_hash = new_oid.hash;
+	memcpy(log.value.update.new_hash, new_oid.hash, GIT_MAX_RAWSZ);
 	if (refs_resolve_ref_unsafe(&create->refs->base, create->refname,
 				    RESOLVE_REF_READING, &old_oid, NULL))
-		log.value.update.old_hash = old_oid.hash;
+		memcpy(log.value.update.old_hash, old_oid.hash, GIT_MAX_RAWSZ);
 
 	ret = reftable_writer_add_log(writer, &log);
-	clear_reftable_log_record(&log);
+	reftable_log_record_release(&log);
 	return ret;
 }
 
@@ -1420,7 +1403,7 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 		logs[logs_nr].update_index = deletion_ts;
 		logs[logs_nr].value.update.message =
 			xstrndup(arg->logmsg, arg->refs->write_options.block_size / 2);
-		logs[logs_nr].value.update.old_hash = old_ref.value.val1;
+		memcpy(logs[logs_nr].value.update.old_hash, old_ref.value.val1, GIT_MAX_RAWSZ);
 		logs_nr++;
 
 		ret = read_ref_without_reload(arg->stack, "HEAD", &head_oid, &head_referent, &head_type);
@@ -1452,7 +1435,7 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 	logs[logs_nr].update_index = creation_ts;
 	logs[logs_nr].value.update.message =
 		xstrndup(arg->logmsg, arg->refs->write_options.block_size / 2);
-	logs[logs_nr].value.update.new_hash = old_ref.value.val1;
+	memcpy(logs[logs_nr].value.update.new_hash, old_ref.value.val1, GIT_MAX_RAWSZ);
 	logs_nr++;
 
 	/*
@@ -1515,10 +1498,6 @@ done:
 	for (i = 0; i < logs_nr; i++) {
 		if (!strcmp(logs[i].refname, "HEAD"))
 			continue;
-		if (logs[i].value.update.old_hash == old_ref.value.val1)
-			logs[i].value.update.old_hash = NULL;
-		if (logs[i].value.update.new_hash == old_ref.value.val1)
-			logs[i].value.update.new_hash = NULL;
 		logs[i].refname = NULL;
 		reftable_log_record_release(&logs[i]);
 	}
@@ -2180,7 +2159,7 @@ static int reftable_be_reflog_expire(struct ref_store *ref_store,
 			dest->value_type = REFTABLE_LOG_DELETION;
 		} else {
 			if ((flags & EXPIRE_REFLOGS_REWRITE) && last_hash)
-				dest->value.update.old_hash = last_hash;
+				memcpy(dest->value.update.old_hash, last_hash, GIT_MAX_RAWSZ);
 			last_hash = logs[i].value.update.new_hash;
 		}
 	}