Disable pushdown if no extension

Pushdowns require functions defined in the extension.

Author: cevian

pkg/pgmodel/migrate.go

@@ -27,6 +27,8 @@ const (
 	metadataUpdateNoExtension   = "INSERT INTO _timescaledb_catalog.metadata(key, value, include_in_telemetry) VALUES ($1, $2, $3) ON CONFLICT (key) DO UPDATE SET value = EXCLUDED.value, include_in_telemetry = EXCLUDED.include_in_telemetry"
 )
 
+var ExtensionIsInstalled = false
+
 type mySrc struct {
 	source.Driver
 }
@@ -137,7 +139,10 @@ func Migrate(db *sql.DB, versionInfo VersionInfo) (err error) {
 
 	_, extErr := db.Exec(fmt.Sprintf(extensionInstall, extSchema))
 	if extErr != nil {
+		ExtensionIsInstalled = false
 		log.Warn("msg", "timescale_prometheus_extra extension not installed", "cause", extErr)
+	} else {
+		ExtensionIsInstalled = true
 	}
 
 	// Insert metadata.

pkg/pgmodel/query_builder.go

@@ -296,7 +296,7 @@ func (t *queryFinalizer) Finalize() (string, []interface{}, error) {
 
 /* The path is the list if ancestors (direct parent last) returned node is the last node processed by the pushdown */
 func getQueryFinalizer(otherClauses string, values []interface{}, hints *storage.SelectHints, path []parser.Node) (*queryFinalizer, parser.Node, error) {
-	if path != nil && hints != nil && len(path) >= 2 && !partOfSubquery(path) {
+	if ExtensionIsInstalled && path != nil && hints != nil && len(path) >= 2 && !partOfSubquery(path) {
 		var topNode parser.Node
 
 		node := path[len(path)-2]