Merge branch 'ps/reftable-iterator-reuse'

Optimize reading random references out of the reftable backend by
allowing reuse of iterator objects.

* ps/reftable-iterator-reuse:
  refs/reftable: reuse iterators when reading refs
  reftable/merged: drain priority queue on reseek
  reftable/stack: add mechanism to notify callers on reload
  refs/reftable: refactor reflog expiry to use reftable backend
  refs/reftable: refactor reading symbolic refs to use reftable backend
  refs/reftable: read references via `struct reftable_backend`
  refs/reftable: figure out hash via `reftable_stack`
  reftable/stack: add accessor for the hash ID
  refs/reftable: handle reloading stacks in the reftable backend
  refs/reftable: encapsulate reftable stack

4 files changed, 23 insertions, 0 deletions

diff --git a/reftable/merged.c b/reftable/merged.c
index 5b93e20f42..bb0836e344 100644
--- a/reftable/merged.c
+++ b/reftable/merged.c
@@ -66,6 +66,8 @@ static int merged_iter_seek(struct merged_iter *mi, struct reftable_record *want
 	int err;
 
 	mi->advance_index = -1;
+	while (!merged_iter_pqueue_is_empty(mi->pq))
+		merged_iter_pqueue_remove(&mi->pq);
 
 	for (size_t i = 0; i < mi->subiters_len; i++) {
 		err = iterator_seek(&mi->subiters[i].iter, want);
diff --git a/reftable/reftable-stack.h b/reftable/reftable-stack.h
index 54787f2ef5..ae14270ea7 100644
--- a/reftable/reftable-stack.h
+++ b/reftable/reftable-stack.h
@@ -149,4 +149,7 @@ struct reftable_compaction_stats {
 struct reftable_compaction_stats *
 reftable_stack_compaction_stats(struct reftable_stack *st);
 
+/* Return the hash of the stack. */
+enum reftable_hash reftable_stack_hash_id(struct reftable_stack *st);
+
 #endif
diff --git a/reftable/reftable-writer.h b/reftable/reftable-writer.h
index c85ef5a5bd..5f9afa620b 100644
--- a/reftable/reftable-writer.h
+++ b/reftable/reftable-writer.h
@@ -68,6 +68,15 @@ struct reftable_write_options {
 	 * fsync(3P) when unset.
 	 */
 	int (*fsync)(int fd);
+
+	/*
+	 * Callback function to execute whenever the stack is being reloaded.
+	 * This can be used e.g. to discard cached information that relies on
+	 * the old stack's data. The payload data will be passed as argument to
+	 * the callback.
+	 */
+	void (*on_reload)(void *payload);
+	void *on_reload_payload;
 };
 
 /* reftable_block_stats holds statistics for a single block type */
diff --git a/reftable/stack.c b/reftable/stack.c
index 10d45e89d0..59fd695a12 100644
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -548,6 +548,10 @@ out:
 		close(fd);
 	free_names(names);
 	free_names(names_after);
+
+	if (st->opts.on_reload)
+		st->opts.on_reload(st->opts.on_reload_payload);
+
 	return err;
 }
 
@@ -1791,3 +1795,8 @@ done:
 	reftable_addition_destroy(add);
 	return err;
 }
+
+enum reftable_hash reftable_stack_hash_id(struct reftable_stack *st)
+{
+	return reftable_merged_table_hash_id(st->merged);
+}