use prev row id for auto random and add a test

lightning/backend/sql2kv.go

@@ -62,7 +62,7 @@ func NewTableKVEncoder(tbl table.Table, options *SessionOptions, chunk *checkpoi
 				if hasSignBit {
 					incrementalBits -= 1
 				}
-				autoRandomBits = rand.New(rand.NewSource(chunk.Chunk.Offset)).Int63n(1<<tbl.Meta().AutoRandomBits) << incrementalBits
+				autoRandomBits = rand.New(rand.NewSource(chunk.Chunk.PrevRowIDMax)).Int63n(1<<tbl.Meta().AutoRandomBits) << incrementalBits
 				break
 			}
 		}

lightning/backend/sql2kv_test.go

@@ -238,7 +238,7 @@ func (s *kvSuite) TestDefaultAutoRandoms(c *C) {
 		SQLMode:          mysql.ModeStrictAllTables,
 		Timestamp:        1234567893,
 		RowFormatVersion: "2",
-	}, &checkpoints.ChunkCheckpoint{Chunk: mydump.Chunk{Offset: 456}})
+	}, &checkpoints.ChunkCheckpoint{Chunk: mydump.Chunk{PrevRowIDMax: 456}})
 	logger := log.Logger{Logger: zap.NewNop()}
 	pairs, err := encoder.Encode(logger, []types.Datum{types.NewStringDatum("")}, 70, []int{-1, 0})
 	c.Assert(err, IsNil)

tests/alter_random/run.sh

@@ -27,7 +27,7 @@ for backend in tidb importer local; do
     run_lightning --backend $backend
 
     run_sql "SELECT count(*) from alter_random.t"
-    check_contains "count(*): 6"
+    check_contains "count(*): 3"
 
     run_sql "SELECT id & b'000001111111111111111111111111111111111111111111111111111111111' as inc FROM alter_random.t"
     check_contains 'inc: 1'
@@ -40,6 +40,6 @@ for backend in tidb importer local; do
     if [ "$backend" = 'tidb' ]; then
       check_contains 'inc: 30002'
     else
-      check_contains 'inc: 7'
+      check_contains 'inc: 4'
     fi
 done

tests/auto_random_default/data/alter_random-schema-create.sql

@@ -0,0 +1 @@
+CREATE DATABASE `alter_random` /*!40100 DEFAULT CHARACTER SET utf8mb4 */;

tests/auto_random_default/data/alter_random.t-schema.sql

@@ -0,0 +1,5 @@
+/*!40103 SET TIME_ZONE='+00:00' */;
+CREATE TABLE `t` (
+  `id` bigint unsigned primary key auto_random,
+  `s` varchar(32)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

tests/auto_random_default/data/alter_random.t.1.sql

@@ -0,0 +1,5 @@
+/*!40103 SET TIME_ZONE='+00:00' */;
+INSERT INTO `t` (`s`) VALUES
+(""),
+(""),
+("");

tests/auto_random_default/run.sh

@@ -0,0 +1,45 @@
+#!/bin/sh
+#
+# Copyright 2020 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.
+
+set -eu
+
+# FIXME: auto-random is only stable on master currently.
+check_cluster_version 4 0 0 AUTO_RANDOM || exit 0
+
+for backend in tidb importer local; do
+    if [ "$backend" = 'local' ]; then
+        check_cluster_version 4 0 0 'local backend' || continue
+    fi
+
+    run_sql 'DROP DATABASE IF EXISTS alter_random;'
+    run_lightning --backend $backend
+
+    run_sql "SELECT count(*) from alter_random.t"
+    check_contains "count(*): 6"
+
+    run_sql "SELECT id & b'000001111111111111111111111111111111111111111111111111111111111' as inc FROM alter_random.t"
+    check_contains 'inc: 1'
+    check_contains 'inc: 2'
+    check_contains 'inc: 3'
+
+    # auto random base is 4
+    run_sql "INSERT INTO alter_random.t VALUES ();"
+    run_sql "SELECT id & b'000001111111111111111111111111111111111111111111111111111111111' as inc FROM alter_random.t"
+    if [ "$backend" = 'tidb' ]; then
+      check_contains 'inc: 30002'
+    else
+      check_contains 'inc: 4'
+    fi
+done