fix: add a subquery comment in *workflowArchive.ListWorkflows

related to 9856df7

Signed-off-by: Xiaofan Hu <[email protected]>

persist/sqldb/workflow_archive.go

@@ -184,6 +184,14 @@ func (r *workflowArchive) ListWorkflows(options sutils.ListOptions) (wfv1.Workfl
 		subSelector = r.session.SQL().Select(db.Raw("*")).From(subSelector).As("x")
 	}
 
+	// why using a subquery: the json unmarshaling process of coalesce
+	// (workflow) is always triggered for every records in the filtering query
+	// in postgres (and maybe mysql as well). by first filtering out uid first
+	// without trying to unmarshal the workflow, it kinda teach the database to
+	// delay the json parsing operation and thus speed up the query (could be
+	// up to 257 times faster for some deployments).
+	//
+	// more context: https://github.com/argoproj/argo-workflows/pull/13566
 	selector := r.session.SQL().Select(selectQuery).From(archiveTableName).Where(
 		r.clusterManagedNamespaceAndInstanceID().And(db.Cond{"uid IN": subSelector}),
 	)