分析 Empty regions 数量增加的原因

问题背景：

通过granfan-->pd-->region health 图表监控到empty region 较多,且此集群目前业务并不多，数据量也很小，初始化时只创建了较表。

问题排查：

查看region merge相关参数：

l max-merge-region-size:

##控制region merge的大小上限，当region大于指定值时pd不会将相邻的region合并(默认20)

l max-merge-region-keys:

##控制region merge的key上限，当region大于指定值时pd不会将相邻的region合并(默认2000)

l merge-schedule-limit:

##同时进行region merge调度的任务数，设置为则关闭region merge(默认值8)

如下，这些参数都是默认值，

$ pd-ctl config show max-merge-region-size |grep max-merge-region-size  

"max-merge-region-size": 20,   

$ pd-ctl config show max-merge-region-keys |grep max-merge-region-keys

    "max-merge-region-keys": 200000,

$ pd-ctl config show merge-schedule-limit |grep merge-schedule-limit

    "merge-schedule-limit": 8,

查看region的split和merge频率相关参数，

l patrol-region-interval:

##控制replicaChecker检查region监控状态的运行频率，越短则运行越快(10ms)

l split-merge-interval:

##控制对同一个region做split和merge的操作间隔，对应新split的region一段时间不会merge(默认1h)

$ pd-ctl config show patrol-region-interval |grep patrol

"patrol-region-interval": "100ms",

$ pd-ctl config show split-merge-interval |grep split

    "split-merge-interval": "1h0m0s",

测试ddl时与分配的region是否会merge:

突然想到，空regions多的集群在ddl时使用了region预分配参数，查看相关表时只有1个region,在社区咨询老师说是被merge了。

创建测试表并预分配region,查看region数是指定的：

mysql> create table guo004(id int, name varchar(10))  SHARD_ROW_ID_BITS=4 PRE_SPLIT_REGIONS=4;

Query OK, 0 rows affected (0.51 sec)

mysql> show table guo004 regions;

+-----------+-----------------------------+-----------------------------+-----------+-----------------+---------------------+------------+---------------+------------+----------------------+------------------+

| REGION_ID | START_KEY                   | END_KEY                     | LEADER_ID | LEADER_STORE_ID | PEERS               | SCATTERING | WRITTEN_BYTES | READ_BYTES | APPROXIMATE_SIZE(MB) | APPROXIMATE_KEYS |

+-----------+-----------------------------+-----------------------------+-----------+-----------------+---------------------+------------+---------------+------------+----------------------+------------------+

|     25373 | t_437_                      | t_437_r_576460752303423488  |     25375 |               5 | 25374, 25375, 25376 |          0 |           341 |          0 |                    1 |                0 |

|     25377 | t_437_r_576460752303423488  | t_437_r_1152921504606846976 |     25379 |               5 | 25378, 25379, 25380 |          0 |            29 |          0 |                    1 |                0 |

|     25381 | t_437_r_1152921504606846976 | t_437_r_1729382256910270464 |     25383 |               5 | 25382, 25383, 25384 |          0 |             0 |          0 |                    1 |                0 |

|     25385 | t_437_r_1729382256910270464 | t_437_r_2305843009213693952 |     25387 |               5 | 25386, 25387, 25388 |          0 |             0 |          0 |                    1 |                0 |

|     25389 | t_437_r_2305843009213693952 | t_437_r_2882303761517117440 |     25391 |               5 | 25390, 25391, 25392 |          0 |            29 |          0 |                    1 |                0 |

|     25393 | t_437_r_2882303761517117440 | t_437_r_3458764513820540928 |     25395 |               5 | 25394, 25395, 25396 |          0 |             0 |          0 |                    1 |                0 |

|     25397 | t_437_r_3458764513820540928 | t_437_r_4035225266123964416 |     25399 |               5 | 25398, 25399, 25400 |          0 |            29 |          0 |                    1 |                0 |

|     25401 | t_437_r_4035225266123964416 | t_437_r_4611686018427387904 |     25403 |               5 | 25402, 25403, 25404 |          0 |             0 |          0 |                    1 |                0 |

|     25405 | t_437_r_4611686018427387904 | t_437_r_5188146770730811392 |     25407 |               5 | 25406, 25407, 25408 |          0 |            29 |          0 |                    1 |                0 |

|     25409 | t_437_r_5188146770730811392 | t_437_r_5764607523034234880 |     25411 |               5 | 25410, 25411, 25412 |          0 |             0 |          0 |                    1 |                0 |

|     25413 | t_437_r_5764607523034234880 | t_437_r_6341068275337658368 |     25415 |               5 | 25414, 25415, 25416 |          0 |            29 |          0 |                    1 |                0 |

|     25417 | t_437_r_6341068275337658368 | t_437_r_6917529027641081856 |     25419 |               5 | 25418, 25419, 25420 |          0 |            29 |          0 |                    1 |                0 |

|     25421 | t_437_r_6917529027641081856 | t_437_r_7493989779944505344 |     25423 |               5 | 25422, 25423, 25424 |          0 |             0 |          0 |                    1 |                0 |

|     25425 | t_437_r_7493989779944505344 | t_437_r_8070450532247928832 |     25427 |               5 | 25426, 25427, 25428 |          0 |            29 |          0 |                    1 |                0 |

|     25429 | t_437_r_8070450532247928832 | t_437_r_8646911284551352320 |     25431 |               5 | 25430, 25431, 25432 |          0 |             0 |          0 |                    1 |                0 |

|     25169 | t_437_r_8646911284551352320 |                             |     25171 |               5 | 25170, 25171, 25172 |          0 |             0 |          0 |                    1 |                0 |

+-----------+-----------------------------+-----------------------------+-----------+-----------------+---------------------+------------+---------------+------------+----------------------+------------------+

16 rows in set (0.01 sec)

检查预分配region是否merge

根据以上split-merge-interval参数，1小时后测试表的guo004空regions将被回收：

mysql> mysql> show table guo004 regions;

+-----------+-----------+---------+-----------+-----------------+---------------------+------------+---------------+------------+----------------------+------------------+

| REGION_ID | START_KEY | END_KEY | LEADER_ID | LEADER_STORE_ID | PEERS               | SCATTERING | WRITTEN_BYTES | READ_BYTES | APPROXIMATE_SIZE(MB) | APPROXIMATE_KEYS |

+-----------+-----------+---------+-----------+-----------------+---------------------+------------+---------------+------------+----------------------+------------------+

|     25425 | t_437_    |         |     25427 |               5 | 25426, 25427, 25428 |          0 |          1285 |          0 |                    1 |                0 |

+-----------+-----------+---------+-----------+-----------------+---------------------+------------+---------------+------------+----------------------+------------------+

1 row in set (0.01 sec)

即使是ddl预分配的region,如果没有regions为空的话，都会自动merge.

查看空regions 信息：

参数说明：

approximate_size：估算的region的数据量大小，单位为MB

approximate_keys：估算的region内的key的个数

注意关注approximate_size、approximate_keys 的值。

查看所有空region信息：

$ ./pd-ctl region check empty-region |more

$ ./pd-ctl region check empty-region |more

{

  "count": 272,

  "regions": [

    {

      "id": 202,

      "start_key": "7480000000000000FF5C00000000000000F8",

"end_key": "7480000000000000FF5E00000000000000F8",

      "epoch": {

        "conf_ver": 71639,

        "version": 43

      },

      "peers": [

        {

          "id": 7796112,

          "store_id": 21

        },

        {

          "id": 7952908,

          "store_id": 2

        },

        {

          "id": 7955094,

          "store_id": 19

        }

      ],

      "leader": {

        "id": 7796112,

        "store_id": 21

      },

      "written_bytes": 0,

      "read_bytes": 0,

      "written_keys": 0,

      "read_keys": 0,

      "approximate_size": 1,

"approximate_keys": 0

    },

    {

      "id": 217800,

      "start_key": "7480000000000002FF8500000000000000F8",

      "end_key": "7480000000000002FF8700000000000000F8",

      "epoch": {

        "conf_ver": 71369,

        "version": 290

      },

      "peers": [

        {

          "id": 7932728,

          "store_id": 3

        },

        {

          "id": 7954710,

          "store_id": 1

        },

        {

          "id": 7955013,

          "store_id": 5

        }

      ],

      "leader": {

"id": 7932728,

        "store_id": 3

      },

      "written_bytes": 0,

      "read_bytes": 0,

      "written_keys": 0,

      "read_keys": 0,

      "approximate_size": 1,

      "approximate_keys": 0

    },

--More--

查看单个region信息：

$ ./pd-ctl  region 217800

$ ./pd-ctl  region 217800

{

  "id": 217800,

  "start_key": "7480000000000002FF8500000000000000F8",

"end_key": "7480000000000002FF8700000000000000F8",

  "epoch": {

    "conf_ver": 71369,

    "version": 290

  },

  "peers": [

    {

      "id": 7932728,

      "store_id": 3

    },

    {

      "id": 7954710,

      "store_id": 1

    },

    {

      "id": 7955013,

      "store_id": 5

    }

  ],

  "leader": {

    "id": 7932728,

    "store_id": 3

  },

  "written_bytes": 0,

  "read_bytes": 0,

  "written_keys": 0,

  "read_keys": 0,

  "approximate_size": 1,

"approximate_keys": 0

}

或者通过系统表TIKV_REGION_STATUS查看：

(我个人更倾向于查系统表，比对的可视度更强些)：

mysql> select REGION_ID,START_KEY,END_KEY,TABLE_ID,DB_NAME,TABLE_NAME,APPROXIMATE_SIZE,APPROXIMATE_KEYS from TIKV_REGION_STATUS where DB_NAME=dzdz or