Merge branch 'ps/reftable-iteration-perf'

The code to iterate over refs with the reftable backend has seen
some optimization.

* ps/reftable-iteration-perf:
  reftable/reader: add comments to `table_iter_next()`
  reftable/record: don't try to reallocate ref record name
  reftable/block: swap buffers instead of copying
  reftable/pq: allocation-less comparison of entry keys
  reftable/merged: skip comparison for records of the same subiter
  reftable/merged: allocation-less dropping of shadowed records
  reftable/record: introduce function to compare records by key

1 files changed, 17 insertions, 9 deletions

diff --git a/reftable/reader.c b/reftable/reader.c
index 2663b03938..b113daab77 100644
--- a/reftable/reader.c
+++ b/reftable/reader.c
@@ -357,24 +357,32 @@ static int table_iter_next(struct table_iter *ti, struct reftable_record *rec)
 
 	while (1) {
 		struct table_iter next = TABLE_ITER_INIT;
-		int err = 0;
-		if (ti->is_finished) {
+		int err;
+
+		if (ti->is_finished)
 			return 1;
-		}
 
+		/*
+		 * Check whether the current block still has more records. If
+		 * so, return it. If the iterator returns positive then the
+		 * current block has been exhausted.
+		 */
 		err = table_iter_next_in_block(ti, rec);
-		if (err <= 0) {
+		if (err <= 0)
 			return err;
-		}
 
+		/*
+		 * Otherwise, we need to continue to the next block in the
+		 * table and retry. If there are no more blocks then the
+		 * iterator is drained.
+		 */
 		err = table_iter_next_block(&next, ti);
-		if (err != 0) {
-			ti->is_finished = 1;
-		}
 		table_iter_block_done(ti);
-		if (err != 0) {
+		if (err) {
+			ti->is_finished = 1;
 			return err;
 		}
+
 		table_iter_copy_from(ti, &next);
 		block_iter_close(&next.bi);
 	}