address comments

Author: lichunzhu

br/pkg/lightning/restore/table_restore.go

@@ -794,7 +794,12 @@ func (tr *TableRestore) postProcess(
 			}
 			hasDupe = hasLocalDupe
 		}
-		failpoint.Inject("SlowDownCheckDupe", func() {})
+		failpoint.Inject("SlowDownCheckDupe", func(v failpoint.Value) {
+			sec := v.(int)
+			tr.logger.Warn("start to sleep several seconds before checking other dupe",
+				zap.Int("seconds", sec))
+			time.Sleep(time.Duration(sec) * time.Second)
+		})
 
 		otherHasDupe, needRemoteDupe, baseTotalChecksum, err := metaMgr.CheckAndUpdateLocalChecksum(ctx, &localChecksum, hasDupe)
 		if err != nil {

br/tests/lightning_duplicate_resolution_incremental/run.sh

@@ -22,14 +22,33 @@ LOG_FILE1="$TEST_DIR/lightning-duplicate-resolution1.log"
 LOG_FILE2="$TEST_DIR/lightning-duplicate-resolution2.log"
 
 # let lightning run a bit slow to avoid some table in the first lightning finish too fast.
-export GO_FAILPOINTS="github.com/pingcap/tidb/br/pkg/lightning/restore/SlowDownCheckDupe=sleep(5000)"
+export GO_FAILPOINTS="github.com/pingcap/tidb/br/pkg/lightning/restore/SlowDownCheckDupe=return(10)"
 run_lightning --backend local --sorted-kv-dir "$TEST_DIR/lightning_duplicate_resolution_incremental.sorted1" \
   --enable-checkpoint=1 --log-file "$LOG_FILE1" --config "tests/$TEST_NAME/config1.toml" &
+
+counter=0
+while [ $counter -lt 10 ]; do
+    if grep -Fq "start to sleep several seconds before checking other dupe" "$LOG_FILE1"; then
+        echo "lightning 1 already starts waiting for dupe"
+        break
+    fi
+    ((counter += 1))
+    echo "waiting for lightning 1 starts"
+    sleep 1
+done
+
+if [ $counter -ge 10 ]; then
+  echo "fail to wait for lightning 1 starts"
+  exit 1
+fi
+
 run_lightning --backend local --sorted-kv-dir "$TEST_DIR/lightning_duplicate_resolution_incremental.sorted2" \
   --enable-checkpoint=1 --log-file "$LOG_FILE2" --config "tests/$TEST_NAME/config2.toml" &
 
 wait
 
+export GO_FAILPOINTS=""
+
 # Ensure table is consistent.
 run_sql 'admin check table dup_resolve_detect.ta'