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This topic has been translated from a Chinese forum by GPT and might contain errors.Original topic: tidb空间大小统计如何理解
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username: 人如其名
[TiDB Usage Environment] Poc
[TiDB Version] 6.3
[Encountered Problem] How to understand space size statistics
Question:
Are the CAPACITY, AVAILABLE, and REGION_SIZE in the tikv_store_status table real-time actual sizes, and are they before or after compression?
The APPROXIMATE_SIZE in the tikv_region_status table is an estimated size. How is this estimate derived?
Do TABLE_ROWS and DATA_LENGTH in the tables table only come from statistics? If the table is large but the statistics are small, will the values always be relatively small?
Are the storage_capacity and storage_size in the METRICS_SCHEMA.pd_cluster_status monitoring view actual sizes? How do they relate to CAPACITY and AVAILABLE in the tikv_store_status table? Which is more accurate, and are they before or after compression?
mysql> select * from tikv_store_status where store_id=1 \G
*************************** 1. row ***************************
STORE_ID: 1
ADDRESS: 127.0.0.1:20160
STORE_STATE: 0
STORE_STATE_NAME: Up
LABEL: null
VERSION: 6.3.0
CAPACITY: 233.5GiB
AVAILABLE: 87.66GiB
LEADER_COUNT: 2
LEADER_WEIGHT: 1
LEADER_SCORE: 2
LEADER_SIZE: 2
REGION_COUNT: 2
REGION_WEIGHT: 1
REGION_SCORE: 6.726269909837314
REGION_SIZE: 2
START_TS: 2022-10-10 13:07:09
LAST_HEARTBEAT_TS: 2022-10-10 15:09:52
UPTIME: 2h2m43.071582s
1 row in set (0.00 sec)
mysql> select * from tikv_region_status limit 1 \G
*************************** 1. row ***************************
REGION_ID: 71
START_KEY:
END_KEY: 7480000000000000FF4600000000000000F8
TABLE_ID: 4
DB_NAME: mysql
TABLE_NAME: user
IS_INDEX: 1
INDEX_ID: 1
INDEX_NAME: PRIMARY
EPOCH_CONF_VER: 1
EPOCH_VERSION: 68
WRITTEN_BYTES: 635
READ_BYTES: 174287
APPROXIMATE_SIZE: 1
APPROXIMATE_KEYS: 1730
REPLICATIONSTATUS_STATE: NULL
REPLICATIONSTATUS_STATEID: NULL
1 row in set (0.01 sec)
mysql> select * from tables limit 1 \G
*************************** 1. row ***************************
TABLE_CATALOG: def
TABLE_SCHEMA: INFORMATION_SCHEMA
TABLE_NAME: REFERENTIAL_CONSTRAINTS
TABLE_TYPE: SYSTEM VIEW
ENGINE: InnoDB
VERSION: 10
ROW_FORMAT: Compact
TABLE_ROWS: 0
AVG_ROW_LENGTH: 0
DATA_LENGTH: 0
MAX_DATA_LENGTH: 0
INDEX_LENGTH: 0
DATA_FREE: 0
AUTO_INCREMENT: NULL
CREATE_TIME: 1970-01-01 08:00:00
UPDATE_TIME: NULL
CHECK_TIME: NULL
TABLE_COLLATION: utf8mb4_bin
CHECKSUM: NULL
CREATE_OPTIONS:
TABLE_COMMENT:
TIDB_TABLE_ID: 4611686018427387918
TIDB_ROW_ID_SHARDING_INFO: NULL
TIDB_PK_TYPE: NONCLUSTERED
TIDB_PLACEMENT_POLICY_NAME: NULL
1 row in set (0.01 sec)
mysql> select * from METRICS_SCHEMA.pd_cluster_status where time=now() and type like 'storage_%';
+----------------------------+----------------+------------------+--------------+
| time | instance | type | value |
+----------------------------+----------------+------------------+--------------+
| 2022-10-10 15:12:28.000000 | 127.0.0.1:2379 | storage_capacity | 501371150336 |
| 2022-10-10 15:12:28.000000 | 127.0.0.1:2379 | storage_size | 303885665 |
+----------------------------+----------------+------------------+--------------+
2 rows in set (0.00 sec)
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