checker: prevent the regions in split-cache from becoming the target …

…of merge (tikv#3454) (tikv#3458)

* cherry pick tikv#3454 to release-3.0

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

* revert

Signed-off-by: HunDunDM <hundundm@gmail.com>

* pick

Signed-off-by: HunDunDM <hundundm@gmail.com>

Co-authored-by: 混沌DM <hundundm@gmail.com>
Co-authored-by: Ti Chi Robot <71242396+ti-chi-bot@users.noreply.github.com>

server/schedule/merge_checker.go

@@ -125,7 +125,7 @@ func (m *MergeChecker) Check(region *core.RegionInfo) []*Operator {
 
 func (m *MergeChecker) checkTarget(region, adjacent, target *core.RegionInfo) *core.RegionInfo {
 	// if is not hot region and under same namespace
-	if adjacent != nil && !m.cluster.IsRegionHot(adjacent.GetID()) &&
+	if adjacent != nil && !m.splitCache.Exists(adjacent.GetID()) && !m.cluster.IsRegionHot(adjacent.GetID()) &&
 		m.classifier.AllowMerge(region, adjacent) &&
 		len(adjacent.GetDownPeers()) == 0 && len(adjacent.GetPendingPeers()) == 0 && len(adjacent.GetLearners()) == 0 {
 		// if both region is not hot, prefer the one with smaller size

server/schedule/merge_checker_test.go

@@ -98,8 +98,8 @@ func (s *testMergeCheckerSuite) SetUpTest(c *C) {
 				},
 			},
 			&metapb.Peer{Id: 109, StoreId: 4},
-			core.SetApproximateSize(10),
-			core.SetApproximateKeys(10),
+			core.SetApproximateSize(1),
+			core.SetApproximateKeys(1),
 		),
 	}
 
@@ -148,6 +148,11 @@ func (s *testMergeCheckerSuite) TestBasic(c *C) {
 	c.Assert(ops[1].RegionID(), Equals, s.regions[3].GetID())
 
 	// Skip recently split regions.
+	ops = s.mc.Check(s.regions[2])
+	c.Assert(ops, NotNil)
+	ops = s.mc.Check(s.regions[3])
+	c.Assert(ops, NotNil)
+
 	s.mc.RecordRegionSplit(s.regions[2].GetID())
 	ops = s.mc.Check(s.regions[2])
 	c.Assert(ops, IsNil)