From ff2b6fbe3516d96257968aa1d7b07351ac37cf44 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@victoriametrics.com>
Date: Wed, 15 May 2024 03:23:33 +0200
Subject: [PATCH] wip

---
 app/vlselect/logsql/logsql.go |  1 +
 lib/logstorage/parser.go      | 27 +++++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/app/vlselect/logsql/logsql.go b/app/vlselect/logsql/logsql.go
index 6cf2b266f0..d7385b642d 100644
--- a/app/vlselect/logsql/logsql.go
+++ b/app/vlselect/logsql/logsql.go
@@ -36,6 +36,7 @@ func ProcessQueryRequest(ctx context.Context, w http.ResponseWriter, r *http.Req
 	if limit > 0 {
 		q.AddPipeLimit(uint64(limit))
 	}
+	q.Optimize()
 
 	tenantIDs := []logstorage.TenantID{tenantID}
 
diff --git a/lib/logstorage/parser.go b/lib/logstorage/parser.go
index b93a9eaeda..9d4e76e09f 100644
--- a/lib/logstorage/parser.go
+++ b/lib/logstorage/parser.go
@@ -215,6 +215,33 @@ func (q *Query) AddPipeLimit(n uint64) {
 	})
 }
 
+// Optimize tries optimizing the query.
+func (q *Query) Optimize() {
+	q.pipes = optimizeSortLimitPipes(q.pipes)
+}
+
+func optimizeSortLimitPipes(pipes []pipe) []pipe {
+	// Merge 'sort ... | limit ...' into 'sort ... limit ...'
+	i := 1
+	for i < len(pipes) {
+		pl, ok := pipes[i].(*pipeLimit)
+		if !ok {
+			i++
+			continue
+		}
+		ps, ok := pipes[i-1].(*pipeSort)
+		if !ok {
+			i++
+			continue
+		}
+		if ps.limit == 0 || pl.n < ps.limit {
+			ps.limit = pl.n
+		}
+		pipes = append(pipes[:i], pipes[i+1:]...)
+	}
+	return pipes
+}
+
 func (q *Query) getNeededColumns() ([]string, []string) {
 	neededFields := newFieldsSet()
 	neededFields.add("*")