fixup! fix: events: address sqlite index selection performance regres…

…sions

chain/events/filter/index.go

@@ -97,11 +97,12 @@ const (
 	// an index that narrows down results to an epoch or a reasonable range of epochs. Specifically,
 	// event_tipset_key_cid or event_height should be the first index. Then further narrowing can take
 	// place within the small subset of results.
-	// Unfortunately SQLite has some quicks in index selection that mean that certain query types will
+	// Unfortunately SQLite has some quirks in index selection that mean that certain query types will
 	// bypass these indexes if alternatives are available. This has been observed specifically on
 	// queries with height ranges: `height>=X AND height<=Y`.
 	//
-	// e.g.:
+	// e.g. we want to see that `event_height` is the first index used in this query:
+	//
 	// EXPLAIN QUERY PLAN
 	// SELECT
 	// 	event.height, event.tipset_key_cid, event_entry.indexed, event_entry.codec, event_entry.key, event_entry.value

chain/events/filter/index_migrations.go

@@ -135,10 +135,11 @@ func migrationVersion2(db *sql.DB, chainStore *store.ChainStore) sqlite.Migratio
 	}
 }
 
-// migrationVersion3 migrates the schema from version 2 to version 3. It originally added two
-// indices: 1) an index on the event.emitter_addr column, and 2) an index on the event_entry.key
-// column. However, as of version 7, these indices have been removed as they were found to be a
-// performance hindrance. This migration is now a no-op.
+// migrationVersion3 migrates the schema from version 2 to version 3 by creating two indices:
+// 1) an index on the event.emitter_addr column, and 2) an index on the event_entry.key column.
+//
+// As of version 7, these indices have been removed as they were found to be a performance
+// hindrance. This migration is now a no-op.
 func migrationVersion3(ctx context.Context, tx *sql.Tx) error {
 	return nil
 }
@@ -154,8 +155,8 @@ func migrationVersion3(ctx context.Context, tx *sql.Tx) error {
 //  1. an index on the event.tipset_key_cid column
 //  2. an index on the event.height column
 //  3. an index on the event.reverted column (removed in version 7)
-//  4. an index on the event_entry.indexed and event_entry.key columns (removed in version 7)
-//  5. an index on the event_entry.codec and event_entry.value columns (removed in version 7)
+//  4. a composite index on the event_entry.indexed and event_entry.key columns (removed in version 7)
+//  5. a composite index on the event_entry.codec and event_entry.value columns (removed in version 7)
 //  6. an index on the event_entry.event_id column
 //
 // Indexes 3, 4, and 5 were removed in version 7 as they were found to be a performance hindrance so
@@ -233,15 +234,15 @@ func migrationVersion6(ctx context.Context, tx *sql.Tx) error {
 // indices:
 //  1. the index on the event.emitter_addr column
 //  2. the index on the event.reverted column
-//  3. the index on the event_entry.indexed and event_entry.key columns
-//  4. the index on the event_entry.codec and event_entry.value columns
+//  3. the composite index on the event_entry.indexed and event_entry.key columns
+//  4. the composite index on the event_entry.codec and event_entry.value columns
 //
 // These indices were found to be a performance hindrance as they prevent SQLite from using the
 // intended initial indexes on height or tipset_key_cid in many query variations. Without additional
 // indices to fall-back on, SQLite is forced to narrow down each query via height or tipset_key_cid
 // which is the desired behavior.
 func migrationVersion7(ctx context.Context, tx *sql.Tx) error {
-	for _, create := range []struct {
+	for _, drop := range []struct {
 		desc  string
 		query string
 	}{
@@ -250,8 +251,8 @@ func migrationVersion7(ctx context.Context, tx *sql.Tx) error {
 		{"drop index event_entry_indexed_key", "DROP INDEX IF EXISTS event_entry_indexed_key;"},
 		{"drop index event_entry_codec_value", "DROP INDEX IF EXISTS event_entry_codec_value;"},
 	} {
-		if _, err := tx.ExecContext(ctx, create.query); err != nil {
-			return xerrors.Errorf("%s: %w", create.desc, err)
+		if _, err := tx.ExecContext(ctx, drop.query); err != nil {
+			return xerrors.Errorf("%s: %w", drop.desc, err)
 		}
 	}