hg_mutation_store: simplify fetching of all predecessors

Summary: Currently we fetch the target mutation entries and then expand them out to their predecessors.  This is left over from the method that used primordial lookups, but is no longer necessary as the recursive CTE can return all that we need.

Reviewed By: mitrandir77

Differential Revision: D54375207

fbshipit-source-id: d7da1f48ac5a3545ba192c171b513bad338b2cf6

eden/mononoke/mercurial/mutation/src/store.rs

@@ -430,13 +430,10 @@ impl SqlHgMutationStore {
         connection: &Connection,
         sql_perf_counter: PerfCounterType,
         entry_set: &mut HgMutationEntrySet,
+        changesets: &HashSet<HgChangesetId>,
     ) -> Result<()> {
-        if entry_set.entries.is_empty() {
-            return Ok(());
-        }
-        let chunks = entry_set
-            .entries
-            .keys()
+        let chunks = changesets
+            .iter()
             .chunks(SELECT_CHAIN_CHUNK_SIZE)
             .into_iter()
             .map(|chunk| chunk.copied().collect::<Vec<_>>())
@@ -605,16 +602,14 @@ impl HgMutationStore for SqlHgMutationStore {
         let (connection, sql_perf_counter) = self
             .read_connection_for_changesets(ctx, &changeset_ids)
             .await?;
-        self.fetch_by_successor(
+        self.fetch_all_predecessors(
             ctx,
             connection,
             sql_perf_counter,
             &mut entry_set,
             &changeset_ids,
         )
         .await?;
-        self.fetch_all_predecessors(ctx, connection, sql_perf_counter, &mut entry_set)
-            .await?;
         let changeset_count = changeset_ids.len();
         let entries = entry_set.into_all_predecessors_by_changeset(changeset_ids);
         debug!(