数据迁移 - 分布式 | 利用 TiDB DM 将数据从 MySQL 迁移至 DBLE - MySQL分布式中间件DBLE

作者：沈光宇
爱可生南区 DBA 团队成员，主要负责 MySQL 故障处理和性能优化。对技术执着，为客户负责。
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一、背景

某客户MySQL实例中数据较大(上T的数据量)，需要将MySQL中数据全量/增量快速迁移至DBLE。TiDB DM支持多线程数据导出导入及增量同步，因此选择了TiDB DM为作数据迁移工具。本文以此案例为背景，介绍使用TiDB DM将数据从MySQL迁移至DBLE的方法及遇到的一些问题。

二、数据迁移示意图及服务器环境

（1）数据迁移示意图如下：

（2）服务器环境如下:

服务器IP	角色	端口	版本	备注
10.186.65.83	dm master	8261/8291	V2.0.7	tiup安装节点
10.186.65.118	dm worker	8262	V2.0.7
10.186.65.14	SRC MySQL	4490	MySQL 8.0.18
10.186.65.4	DBLE	8066	DBLE 3.21.10.6
10.186.65.61	DBLE datanode	4408	MySQL 8.0.25
10.186.65.65	DBLE datanode	4408	MySQL 8.0.25

三、安装 TiDB DM

（1）准备环境及安装 tiup

#分别在dm master和worker节点主机创建tidb用户,密码为dmadmin,并配置sudo
shell> useradd tidb
shell> echo "dmadmin" | passwd tidb --stdin
shell> echo "tidb ALL=(ALL) NOPASSWD: ALL" > /etc/sudoers.d/tidb

#切换至tidb用户,生成密钥，并做ssh信任,dm集群内机器都需要做ssh信任
shell> su - tidb
shell> ssh-keygen -t rsa
shell> ssh-copy-id -i ~/.ssh/id_rsa.pub tidb@10.186.65.118
shell> ssh-copy-id -i ~/.ssh/id_rsa.pub tidb@10.186.65.83

#安装tiup,在tidb用户下
shell> curl --proto '=https' --tlsv1.2 -sSf https://tiup-mirrors.pingcap.com/install.sh | sh
shell> source .bash_profile
shell> which tiup
~/.tiup/bin/tiup

#安装dmctl
shell> tiup install dm dmctl:v2.0.7
component dm version v1.10.2 is already installed
download https://tiup-mirrors.pingcap.com/dmctl-v2.0.7-linux-amd64.tar.gz 26.92 MiB / 26.92 MiB 100.00% 10.01 MiB/s

（2）安装dm-cluster

#生成配置模版
shell> tiup dm template > dm_topology.yaml
#修改后配置文件如下：
shell> cat dm_topology.yaml  |grep -v ^[#-] |grep -v ^$
global:
  user: "tidb"
  ssh_port: 22
  deploy_dir: "/home/tidb/dm/deploy"
  data_dir: "/home/tidb/dm/data"
master_servers:
  - host: 10.186.65.83
worker_servers:
  - host: 10.186.65.118
monitoring_servers:
  - host: 10.186.65.83
grafana_servers:
  - host: 10.186.65.83
alertmanager_servers:
  - host: 10.186.65.83
  
#安装、并启动DM集群
shell> tiup dm deploy dm-test v2.0.7 ./dm_topology.yaml --user tidb -i /home/tidb/.ssh/id_rsa
shell> tiup dm start dm-test
#查看DM集群
[tidb@10_186_65_83 ~]$ tiup dm display dm-test
tiup is checking updates for component dm ...
Starting component `dm`: /home/tidb/.tiup/components/dm/v1.10.2/tiup-dm display dm-test
Cluster type:       dm
Cluster name:       dm-test
Cluster version:    v2.0.7
Deploy user:        tidb
SSH type:           builtin
Grafana URL:        http://10.186.65.83:3000
ID                  Role          Host           Ports      OS/Arch       Status     Data Dir                              Deploy Dir
--                  ----          ----           -----      -------       ------     --------                              ----------
10.186.65.83:9093   alertmanager  10.186.65.83   9093/9094  linux/x86_64  Up         /home/tidb/dm/data/alertmanager-9093  /home/tidb/dm/deploy/alertmanager-9093
10.186.65.83:8261   dm-master     10.186.65.83   8261/8291  linux/x86_64  Healthy|L  /home/tidb/dm/data/dm-master-8261     /home/tidb/dm/deploy/dm-master-8261
10.186.65.118:8262  dm-worker     10.186.65.118  8262       linux/x86_64  Free       /home/tidb/dm/data/dm-worker-8262     /home/tidb/dm/deploy/dm-worker-8262
10.186.65.83:3000   grafana       10.186.65.83   3000       linux/x86_64  Up         -                                     /home/tidb/dm/deploy/grafana-3000
10.186.65.83:9090   prometheus    10.186.65.83   9090       linux/x86_64  Up         /home/tidb/dm/data/prometheus-9090    /home/tidb/dm/deploy/prometheus-9090
Total nodes: 5

四、DBLE端配置

（1）db.xml

<?xml version="1.0"?>
<dble:db xmlns:dble="http://dble.cloud/">
    <dbGroup name="dbGroup1" rwSplitMode="0" delayThreshold="-1">
        <heartbeat>select 1</heartbeat>
        <dbInstance name="host_1" url="10.186.65.61:4408" user="sgy" password="QfnHoIeIYL7ZT+EdJMYNuiLw6glbx2hEyrqxK+uxFPU8vja8vZHCLEKvKBOt1vOJdXCCgW7wNidJaTYWORDaUg==" maxCon="2000" minCon="50" primary="true"  usingDecrypt="true"></dbInstance>
    </dbGroup>
    <dbGroup name="dbGroup2" rwSplitMode="0" delayThreshold="-1">
        <heartbeat>select 1</heartbeat>
        <dbInstance name="host_2" url="10.186.65.65:4408" user="sgy" password="d+rG/82+4h21ARS8D6Gu5MIFQ2UBC0h+ZS0EI7bvWAtTJUBsKuFY8+AVZtW1pZk+qtISoI2WpVt29Z9eqMRP5A==" maxCon="2000" minCon="50" primary="true"  usingDecrypt="true"></dbInstance>
    </dbGroup>
</dble:db>
#注：用户密码为加密后的字符串

（2）sharding.xml

<?xml version="1.0"?>
<dble:sharding xmlns:dble="http://dble.cloud/" >
    <schema name="dm_meta" sqlMaxLimit="-1">
        <singleTable name="mysql_sync_to_dble_loader_checkpoint" shardingNode="dm_meta" />
        <singleTable name="mysql_sync_to_dble_syncer_checkpoint" shardingNode="dm_meta" />
    </schema>
    <schema name="sbtest" sqlMaxLimit="-1">
        <shardingTable name="sbtest1" shardingNode="dn1,dn2,dn3,dn4" sqlMaxLimit="-1" shardingColumn="id" function="pro_func_jumpHash"></shardingTable>
        <shardingTable name="sbtest2" shardingNode="dn1,dn2,dn3,dn4" sqlMaxLimit="-1" shardingColumn="id" function="pro_func_jumpHash"></shardingTable>
        <shardingTable name="t1" shardingNode="dn1,dn2,dn3,dn4" sqlMaxLimit="-1" shardingColumn="c1" function="pro_func_jumpHash"></shardingTable>
        <shardingTable name="t2" shardingNode="dn1,dn2,dn3,dn4" sqlMaxLimit="-1" shardingColumn="c1" function="pro_func_jumpHash"></shardingTable>
    </schema>

    <shardingNode name="dn1" dbGroup="dbGroup1" database="dh_dn1"></shardingNode>
    <shardingNode name="dn2" dbGroup="dbGroup1" database="dh_dn2"></shardingNode>
     <shardingNode name="dn3" dbGroup="dbGroup2" database="dh_dn3"></shardingNode>
    <shardingNode name="dn4" dbGroup="dbGroup2" database="dh_dn4"></shardingNode>
    <shardingNode name="dm_meta" dbGroup="dbGroup1" database="dm_meta"/>
    
    <function name="pro_func_jumpHash" class="jumpStringHash">
        <property name="partitionCount">4</property>
        <property name="hashSlice">0:0</property>
    </function>

</dble:sharding>
注：需要提前配置好DM同步时保存数据的schema及两张表,表名分别是
dm同步任务名 + _loader_checkpoint 即表mysql_sync_to_dble_loader_checkpoint
dm同步任务名 + _syncer_checkpoint 即表mysql_sync_to_dble_syncer_checkpoint

（3）user.xml

<?xml version="1.0"?>
<dble:user xmlns:dble="http://dble.cloud/">
    <managerUser name="root" password="RYQdYYnzbcZlDuhV4LhJxFTM8kbU3d0y183LU+FgRWzNscvvvFPcdmeEKMdswMyzIaA+kObcozliHEYAlT0AjA==" usingDecrypt="true"></managerUser>
    <shardingUser name="sz" schemas="sbtest,dm_meta" password="jyaXmGFU+mdTGbUZIVbdEcVwItLPI+Yjxdq4wkOzhAYRB29WGZJd0/PkTJh3ky/v4E2yYoqgUzJXPzPRPiQF0Q==" usingDecrypt="true" readOnly="false" maxCon="1000"></shardingUser>
</dble:user>
#注：用户密码为加密后的字符串

（4）登陆 DBLE 管理端执行创建物理数据库命令

shell> /data/mysql/base/5.7.36/bin/mysql -uroot -padmin -h 10.186.65.4 -P 9066
dble> create database @@shardingNode = 'dn$1-4';
Query OK, 1 row affected (0.06 sec)

dble> create database @@shardingNode = 'dm_meta';
Query OK, 1 row affected (0.01 sec)

五、在源端 MySQL 压测创建测试数据

#执行prepare，初始化100W行数据
 /usr/share/sysbench/oltp_insert.lua --mysql-db=sbtest --mysql-host=10.186.65.14 --mysql-port=4490  --mysql-user=sgy --mysql-password=admin  --tables=2 --table-size=1000000 --threads=16 --time=60 --report-interval=1 --max-requests=0 --percentile=95 --mysql-ignore-errors=1062   prepare
sysbench 1.0.17 (using system LuaJIT 2.0.4)

Initializing worker threads...

Creating table 'sbtest1'...
Creating table 'sbtest2'...
Inserting 1000000 records into 'sbtest2'
Inserting 1000000 records into 'sbtest1'
Creating a secondary index on 'sbtest2'...
Creating a secondary index on 'sbtest1'...

#利用sysbench不断写入数据
shell> /usr/share/sysbench/oltp_read_write.lua --mysql-db=sbtest --mysql-host=10.186.65.14 --mysql-port=4490  --mysql-user=sgy --mysql-password=admin  --tables=2 --table-size=2000000 --threads=16 --time=6000 --report-interval=1 --max-requests=0 --percentile=95 --mysql-ignore-errors=1062   run
sysbench 1.0.17 (using system LuaJIT 2.0.4)

Running the test with following options:
Number of threads: 16
Report intermediate results every 1 second(s)
Initializing random number generator from current time


Initializing worker threads...

Threads started!

[ 1s ] thds: 16 tps: 585.44 qps: 11916.49 (r/w/o: 8360.33/1282.63/2273.53) lat (ms,95%): 55.82 err/s: 0.00 reconn/s: 0.00
[ 2s ] thds: 16 tps: 744.18 qps: 14819.02 (r/w/o: 10379.16/1609.36/2830.50) lat (ms,95%): 41.85 err/s: 0.00 reconn/s: 0.00
[ 3s ] thds: 16 tps: 605.11 qps: 12144.20 (r/w/o: 8500.54/1321.24/2322.42) lat (ms,95%): 47.47 err/s: 0.00 reconn/s: 0.00
[ 4s ] thds: 16 tps: 773.91 qps: 15558.16 (r/w/o: 10881.71/1737.79/2938.65) lat (ms,95%): 41.10 err/s: 0.00 reconn/s: 0.00

六、启动数据同步任务

（1）配置数据源

#使用dmctl工具生成密码加密字符串,每次执行都会产生不同的加密字符串
shell> tiup dmctl encrypt 'admin'
dmXgktpuF18RP1mDN/B2UkA6pDN9PQ==

#mysql数据库配置文件如下
shell> cat mysql_source_14_4490.yaml
source-id: "mysql_source_14_4490"
from:
  host: "10.186.65.14"
  port: 4490
  user: "sgy"
  password: "dmXgktpuF18RP1mDN/B2UkA6pDN9PQ=="
  
#创建数据源
shell> tiup dmctl --master-addr 10.186.65.83:8261  operate-source create ./mysql_source_14_4490.yaml
Starting component `dmctl`: /home/tidb/.tiup/components/dmctl/v2.0.7/dmctl/dmctl --master-addr 10.186.65.83:8261 operate-source create ./mysql_source_14_4490.yaml
{
    "result": true,
    "msg": "",
    "sources": [
        {
            "result": true,
            "msg": "",
            "source": "mysql_source_14_4490",
            "worker": "dm-10.186.65.118-8262"
        }
    ]
}

#查看数据源
shell> tiup dmctl --master-addr 10.186.65.83:8261  operate-source show
{
    "result": true,
    "msg": "",
    "sources": [
        {
            "result": true,
            "msg": "",
            "source": "mysql_source_14_4490",
            "worker": "dm-10.186.65.118-8262"
        }
    ]
}

（2）配置同步任务

#同步配置文件如下
shell> cat mysql_sync_to_dble.yaml
name: "mysql_sync_to_dble"      #同步任务名
task-mode: "all"                #全量 + Binlog 实时同步
clean-dump-file: true
timezone: "Asia/Shanghai"
ignore-checking-items: ["auto_increment_ID"]
target-database:
  host: "10.186.65.4"           #DBLE主机IP地址
  port: 8066                    #DBLE流量端口
  user: "sz"                    #连接DBLE的用户
  password: "KRfSNtdxe63tehpnCYoCz0ABdUGivg=="    #连接DBLE用户密码，用tiup dmctl encrypt 'password'生成

mysql-instances:
-
  source-id: "mysql_source_14_4490"
  block-allow-list: "global"
  mydumper-config-name: "global"
  loader-config-name:   "global"
  syncer-config-name: "global"

block-allow-list:
  global:
    do-dbs: ["sbtest"]            #只迁移sbtest库

mydumpers:
  global:
    extra-args: "-B sbtest"      #只dump sbtest库

loaders:
  global:
    pool-size: 8

syncers:
  global:
    worker-count: 8

#更详细配置说明参考官方文档：
https://docs.pingcap.com/zh/tidb-data-migration/v2.0/task-configuration-file-full#%E5%AE%8C%E6%95%B4%E9%85%8D%E7%BD%AE%E6%96%87%E4%BB%B6%E7%A4%BA%E4%BE%8B

#检查配置文件
shell> tiup dmctl:v2.0.7 --master-addr=10.186.65.83:8261  check-task ./mysql_sync_to_dble.yaml
Starting component `dmctl`: /home/tidb/.tiup/components/dmctl/v2.0.7/dmctl/dmctl --master-addr=10.186.65.83:8261 check-task ./mysql_sync_to_dble.yaml
{
    "result": true,
    "msg": "check pass!!!"
}

#启动同步任务
shell> tiup dmctl:v2.0.7 --master-addr=10.186.65.83:8261  start-task ./mysql_sync_to_dble.yaml
Starting component `dmctl`: /home/tidb/.tiup/components/dmctl/v2.0.7/dmctl/dmctl --master-addr=10.186.65.83:8261 start-task ./mysql_sync_to_dble.yaml
{
    "result": true,
    "msg": "",
    "sources": [
        {
            "result": true,
            "msg": "",
            "source": "mysql_source_14_4490",
            "worker": "dm-10.186.65.118-8262"
        }
    ]
}

#在dm-worker节点查看导出的SQL文件, 
shell> ls -lh /home/tidb/dm/deploy/dm-worker-8262/dumped_data.mysql_sync_to_dble
total 384M
-rw-r--r-- 1 tidb tidb 187 Aug  5 14:04 metadata
-rw-r--r-- 1 tidb tidb 48M Aug  5 14:04 sbtest.sbtest1.0000000000000.sql
-rw-r--r-- 1 tidb tidb 48M Aug  5 14:04 sbtest.sbtest1.0000000010000.sql
-rw-r--r-- 1 tidb tidb 48M Aug  5 14:04 sbtest.sbtest1.0000000020000.sql
-rw-r--r-- 1 tidb tidb 48M Aug  5 14:04 sbtest.sbtest1.0000000030000.sql
-rw-r--r-- 1 tidb tidb 369 Aug  5 14:04 sbtest.sbtest1-schema.sql
-rw-r--r-- 1 tidb tidb 48M Aug  5 14:04 sbtest.sbtest2.0000000000000.sql
-rw-r--r-- 1 tidb tidb 48M Aug  5 14:04 sbtest.sbtest2.0000000010000.sql
-rw-r--r-- 1 tidb tidb 48M Aug  5 14:04 sbtest.sbtest2.0000000020000.sql
-rw-r--r-- 1 tidb tidb 48M Aug  5 14:04 sbtest.sbtest2.0000000030000.sql
-rw-r--r-- 1 tidb tidb 369 Aug  5 14:04 sbtest.sbtest2-schema.sql
-rw-r--r-- 1 tidb tidb 152 Aug  5 14:04 sbtest-schema-create.sql

#创建库SQL文件
shell> head /home/tidb/dm/deploy/dm-worker-8262/dumped_data.mysql_sync_to_dble/sbtest-schema-create.sql
/*!40101 SET NAMES binary*/;
CREATE DATABASE `sbtest` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_bin */ /*!80016 DEFAULT ENCRYPTION='N' */;

#创建表SQL文件
shell> head /home/tidb/dm/deploy/dm-worker-8262/dumped_data.mysql_sync_to_dble/sbtest.sbtest1-schema.sql
/*!40101 SET NAMES binary*/;
CREATE TABLE `sbtest1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `k` int(11) NOT NULL DEFAULT '0',
  `c` char(120) COLLATE utf8mb4_bin NOT NULL DEFAULT '',
  `pad` char(60) COLLATE utf8mb4_bin NOT NULL DEFAULT '',
  PRIMARY KEY (`id`),
  KEY `k_1` (`k`)
) ENGINE=InnoDB AUTO_INCREMENT=1000001 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;

#dump生成批量插入数据SQL文件
shell> head /home/tidb/dm/deploy/dm-worker-8262/dumped_data.mysql_sync_to_dble/sbtest.sbtest1.0000000000000.sql
/*!40101 SET NAMES binary*/;
INSERT INTO `sbtest1` (`id`,`k`,`c`,`pad`) VALUES
(1,498670,'31451373586-15688153734-79729593694-96509299839-83724898275-86711833539-78981337422-35049690573-51724173961-87474696253','98996621624-36689827414-04092488557-09587706818-65008859162'),
(2,497778,'21472970079-70972780322-70018558993-71769650003-09270326047-32417012031-10768856803-14235120402-93989080412-18690312264','04776826683-45880822084-77922711547-29057964468-76514263618'),
(3,498956,'49376827441-24903985029-56844662308-79012577859-40518387141-60588419212-24399130405-42612257832-29494881732-71506024440','26843035807-96849339132-53943793991-69741192222-48634174017'),
(4,518727,'85762858421-36258200885-10758669419-44272723583-12529521893-95630803635-53907705724-07005352902-43001596772-53048338959','37979424284-37912826784-31868864947-42903702727-96097885121'),
(5,502480,'24805466175-85245528617-94635882649-46305216925-28637832581-03224489581-68883711727-95491561683-91969681472-12022277774','19288959552-55556468076-14192290426-55457672510-18043372364'),
(6,500774,'52892836230-54177743992-01821871718-48412537487-30066596248-87215430797-00375777469-64498831720-58542556455-90784765418','59487960480-08453890592-99628797439-16757639138-29377916560'),
(7,501466,'85820931248-14475640036-11980694501-86588543167-31029306229-09626867980-90685354565-02350460358-25863585366-53793794448','26081374730-86321700986-51212137094-30635959762-03880194434'),
(8,497838,'81578049255-33453976301-67096870761-27658738403-30546242249-53677469854-26594573136-34292002037-52736825353-99165193170','64289062455-51067794311-09919261228-11533354367-07401173317'),

（3）查看同步任务状态

shell> tiup dmctl:v2.0.7 --master-addr=10.186.65.83:8261  query-status ./mysql_sync_to_dble.yaml
Starting component `dmctl`: /home/tidb/.tiup/components/dmctl/v2.0.7/dmctl/dmctl --master-addr=10.186.65.83:8261 query-status ./mysql_sync_to_dble.yaml
{
    "result": true,
    "msg": "",
    "sources": [
        {
            "result": true,
            "msg": "",
            "sourceStatus": {
                "source": "mysql_source_14_4490",
                "worker": "dm-10.186.65.118-8262",
                "result": null,
                "relayStatus": null
            },
            "subTaskStatus": [
                {
                    "name": "mysql_sync_to_dble",
                    "stage": "Running",
                    "unit": "Sync",
                    "result": null,
                    "unresolvedDDLLockID": "",
                    "sync": {
                        "totalEvents": "425355",
                        "totalTps": "1203",
                        "recentTps": "2386",
                        "masterBinlog": "(mysql-bin.000027, 76114275)",
                        "masterBinlogGtid": "c7827165-bf89-11ec-92e6-02000aba410e:1-5091258",
                        "syncerBinlog": "(mysql-bin.000026, 229462770)",
                        "syncerBinlogGtid": "",
                        "blockingDDLs": [
                        ],
                        "unresolvedGroups": [
                        ],
                        "synced": false,
                        "binlogType": "remote",
                        "secondsBehindMaster": "38"
                    }
                }
            ]
        }
    ]
}

七、验证数据

#暂停先前执行的sysbench程序，确保dm同步与源端无延迟时，对表作count(*)
#在源端MySQL，对表进行count(*)
mysql> select count(*) from sbtest.sbtest1;
+----------+
| count(*) |
+----------+
|  1116471 |
+----------+
1 row in set (0.68 sec)

mysql> select count(*) from sbtest.sbtest2;
+----------+
| count(*) |
+----------+
|  1117020 |
+----------+
1 row in set (0.54 sec)

#通过dble对表进行count(*)
dble> select count(*) from sbtest.sbtest1;
+----------+
| count(*) |
+----------+
|  1116471 |
+----------+
1 row in set (1.04 sec)

dble> select count(*) from sbtest.sbtest2;
+----------+
| count(*) |
+----------+
|  1117020 |
+----------+
1 row in set (1.58 sec)

#在源端数据进行更新操作
mysql> update sbtest.sbtest1 set c=uuid() where id=20;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from sbtest.sbtest1 where id=20;
+----+--------+--------------------------------------+-------------------------------------------------------------+
| id | k      | c                                    | pad                                                         |
+----+--------+--------------------------------------+-------------------------------------------------------------+
| 20 | 501448 | 24649f0f-14d1-11ed-b4f2-02000aba410e | 91052688950-96415657187-00012408429-12357288330-41295735957 |
+----+--------+--------------------------------------+-------------------------------------------------------------+
1 row in set (0.00 sec)

#通过dble查询数据
dble> select * from sbtest.sbtest1 where id=20;
+----+--------+--------------------------------------+-------------------------------------------------------------+
| id | k      | c                                    | pad                                                         |
+----+--------+--------------------------------------+-------------------------------------------------------------+
| 20 | 501448 | 24649f0f-14d1-11ed-b4f2-02000aba410e | 91052688950-96415657187-00012408429-12357288330-41295735957 |
+----+--------+--------------------------------------+-------------------------------------------------------------+
1 row in set (0.01 sec)

八、注意事项

（1）TiDB DM版本要求：TiDB DM v2.0.7

（2）在进行数据量导入时需要关闭DBLE慢查询日志

#由于数据同步在全量导入阶段会产生大量慢查询，需要在执行同步任务之前先关闭DBLE的慢查询日志
shell> mysql --prompt='dble>' -uroot -p -h 10.186.65.4 -P 9066
#查看慢查询日志状态，1表示开启，0表示关闭
dble> show @@slow_query_log;   
+------------------+
| @@slow_query_log |
+------------------+
| 1                |
+------------------+
1 row in set (0.00 sec)
 
#全量数据导入前，关闭dble慢查询日志
dble> disable @@slow_query_log;
Query OK, 1 row affected (0.01 sec)
disable slow_query_log success
 
#待全量数据导入完成后，开启dble慢查询日志
dble> enable @@slow_query_log;
Query OK, 1 row affected (0.01 sec)
enable slow_query_log success

（3）检查源端 MySQL 实例上是否有运行类似 pt-kill 的程序

#如果在源端MySQL实例上运行有pt-kill或类似的程序，DM同步任务在执行全量数据dump阶段，
导出线程可能会被程序kill掉，导致全备失败。dm-worker.log日志如下：
[ERROR] [subtask.go:311] ["unit process error"] [subtask=oms-sync-receiver] [unit=Dump] ["error information"="{\"ErrCode\":32001,\"ErrClass\":\"dump-unit\",\"ErrScope\":\"internal\",\"ErrLevel\":\"high\",\"Message\":\"mydumper/dumpling runs with error, with output (may empty): \",\"RawCause\":\"invalid connection\"}"]

解决方法：先将pt-kill实用工具停止，然后再重新运行TiDM同步任务，待全量数据dump完成后在开启pt-kill。

（4）迁移时如需对目标表表结构进行修改，如源表有建立分区而目标表通过分片后不需要建立分区、修改表字符集(建议使用utf8mb4)等，可先将表结构从源库导出，修改后导入 DBLE 或导入 DBLE 后在修改表结构，最后再开启 DM 同步任务。

（5）源、目标表字段顺序必须要一致，否则可能会导致数据不一致，两字段同为 varchar 并且长度不相等时，同步任务并不会报错，但写入目标表的值可能会被截断，如下图：

DM 任务启动后连接目标端时，会将 session 级别 sql_mode 设置成下面值：
sql_mode='IGNORE_SPACE,NO_AUTO_VALUE_ON_ZERO,NO_ENGINE_SUBSTITUTION,ALLOW_INVALID_DATES,ONLY_FULL_GROUP_BY'；

分布式 | 利用 TiDB DM 将数据从 MySQL 迁移至 DBLE