statistics: fix panic when move analyze jobs to history (#10286)

statistics/analyze_jobs.go

@@ -63,7 +63,7 @@ func MoveToHistory(job *AnalyzeJob) {
 	analyzeStatus.Lock()
 	delete(analyzeStatus.jobs, job)
 	analyzeStatus.history = append(analyzeStatus.history, job)
-	numJobs := len(analyzeStatus.jobs)
+	numJobs := len(analyzeStatus.history)
 	if numJobs > numMaxHistoryJobs {
 		analyzeStatus.history = analyzeStatus.history[numJobs-numMaxHistoryJobs:]
 	}

statistics/analyze_jobs_test.go

@@ -0,0 +1,34 @@
+// Copyright 2019 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package statistics
+
+import (
+	. "github.com/pingcap/check"
+)
+
+func (s *testStatisticsSuite) TestMoveToHistory(c *C) {
+	numJobs := numMaxHistoryJobs*2 + 1
+	jobs := make([]*AnalyzeJob, 0, numJobs)
+	for i := 0; i < numJobs; i++ {
+		job := &AnalyzeJob{}
+		AddNewAnalyzeJob(job)
+		jobs = append(jobs, job)
+	}
+	MoveToHistory(jobs[0])
+	c.Assert(len(GetAllAnalyzeJobs()), Equals, numJobs)
+	for i := 1; i < numJobs; i++ {
+		MoveToHistory(jobs[i])
+	}
+	c.Assert(len(GetAllAnalyzeJobs()), Equals, numMaxHistoryJobs)
+}