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- Glossary
DATA_LOCK_WAITS
The DATA_LOCK_WAITS
table shows the ongoing pessimistic locks waiting on all TiKV nodes in the cluster.
Currently, this is an experimental feature. The definition and behavior of the table structure might have major changes in future releases.
USE information_schema;
DESC data_lock_waits;
+------------------------+---------------------+------+------+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------------------+---------------------+------+------+---------+-------+
| KEY | varchar(64) | NO | | NULL | |
| TRX_ID | bigint(21) unsigned | NO | | NULL | |
| CURRENT_HOLDING_TRX_ID | bigint(21) unsigned | NO | | NULL | |
| SQL_DIGEST | varchar(64) | YES | | NULL | |
+------------------------+---------------------+------+------+---------+-------+
The meaning of each column field in the DATA_LOCK_WAITS
table is as follows:
KEY
: The KEY that is waiting for the lock and displayed in the form of hexadecimal string.TRX_ID
: The ID of the transaction that is waiting for the lock. This ID is also thestart_ts
of the transaction.CURRENT_HOLDING_TRX_ID
: The ID of the transaction that currently holds the lock. This ID is also thestart_ts
of the transaction.SQL_DIGEST
: The digest of the SQL statement that is currently blocked in the lock-waiting transaction.
- The information in this table is obtained in real time from all TiKV nodes during the query. Currently, even if the
WHERE
condition is added, TiDB might still collect information from all TiKV nodes. If the cluster is large and the load is high, querying this table might cause a potential risk of performance jitter. Therefore, use this table according to your actual situation. - The information from different TiKV nodes is NOT guaranteed to be the snapshot at the same point in time.
Example
select * from information_schema.data_lock_waits\G
*************************** 1. row ***************************
KEY: 7480000000000000355f728000000000000002
TRX_ID: 425405024158875649
CURRENT_HOLDING_TRX_ID: 425405016242126849
SQL_DIGEST: f7530877a35ae65300c42250abd8bc731bbaf0a7cabc05dab843565230611bb22
2 rows in set (0.01 sec)
The above query result shows that the transaction of the ID 425405024158875649
was trying to obtain the pessimistic lock on the key 7480000000000000355f728000000000000002
when the statement with digest "f7530877a35ae65300c42250abd8bc731bbaf0a7cabc05dab843565230611bb22"
was being executed, but the lock on this key was held by the transaction of the ID 425405016242126849
.
SQL Digest
The DATA_LOCK_WAITS
table records the SQL digest but not the original SQL statement.
SQL digest is the hash value of the normalized SQL statement. To find the original SQL statement corresponding to the SQL digest, perform one of the following operations:
- For the statements executed on the current TiDB node in the recent period of time, you can find the corresponding original SQL statement in the
STATEMENTS_SUMMARY
orSTATEMENTS_SUMMARY_HISTORY
table according to the SQL digest. - For the statements executed on all TiDB nodes in the entire cluster in the recent period of time, you can find the corresponding SQL statement in the
CLUSTER_STATEMENTS_SUMMARY
orCLUSTER_STATEMENTS_SUMMARY_HISTORY
table according to the SQL digest.
select digest, digest_text from information_schema.statements_summary where digest = "f7530877a35ae65300c42250abd8bc731bbaf0a7cabc05dab843565230611bb2";
+------------------------------------------------------------------+---------------------------------------+
| digest | digest_text |
+------------------------------------------------------------------+---------------------------------------+
| f7530877a35ae65300c42250abd8bc731bbaf0a7cabc05dab843565230611bb2 | update `t` set `v` = ? where `id` = ? |
+------------------------------------------------------------------+---------------------------------------+
For detailed description of SQL digest, STATEMENTS_SUMMARY
, STATEMENTS_SUMMARY_HISTORY
, CLUSTER_STATEMENTS_SUMMARY
, and CLUSTER_STATEMENTS_SUMMARY_HISTORY
tables, see Statement Summary Tables.