Sign InTry Free

TiDB Specific Functions

The following functions are TiDB extensions, and are not present in MySQL:

Function nameFunction description
TIDB_BOUNDED_STALENESS()The TIDB_BOUNDED_STALENESS function instructs TiDB to read the data as new as possible within the time range. See also: Read Historical Data Using the AS OF TIMESTAMP Clause
TIDB_DECODE_KEY(str)The TIDB_DECODE_KEY function can be used to decode a TiDB-encoded key entry into a JSON structure containing _tidb_rowid and table_id. These encoded keys can be found in some system tables and in logging outputs.
TIDB_DECODE_PLAN(str)The TIDB_DECODE_PLAN function can be used to decode a TiDB execution plan.
TIDB_IS_DDL_OWNER()The TIDB_IS_DDL_OWNER function can be used to check whether or not the TiDB instance you are connected to is the one that is the DDL Owner. The DDL Owner is the TiDB instance that is tasked with executing DDL statements on behalf of all other nodes in the cluster.
TIDB_PARSE_TSO(num)The TIDB_PARSE_TSO function can be used to extract the physical timestamp from a TiDB TSO timestamp. See also: tidb_current_ts.
TIDB_VERSION()The TIDB_VERSION function returns the TiDB version with additional build information.
VITESS_HASH(str)The VITESS_HASH function returns the hash of a string that is compatible with Vitess' HASH function. This is intended to help the data migration from Vitess.

Examples

This section provides examples for some of the functions above.

TIDB_DECODE_KEY

In the following example, the table t1 has a hidden rowid that is generated by TiDB. The TIDB_DECODE_KEY is used in the statement. From the result, you can see that the hidden rowid is decoded and output, which is a typical result for the non-clustered primary key.

SELECT START_KEY, TIDB_DECODE_KEY(START_KEY) FROM information_schema.tikv_region_status WHERE table_name='t1' AND REGION_ID=2\G
*************************** 1. row *************************** START_KEY: 7480000000000000FF3B5F728000000000FF1DE3F10000000000FA TIDB_DECODE_KEY(START_KEY): {"_tidb_rowid":1958897,"table_id":"59"} 1 row in set (0.00 sec)

In the following example, the table t2 has a compound clustered primary key. From the JSON output, you can see a handle that contains the name and value for both of the columns that are part of the primary key.

show create table t2\G
*************************** 1. row *************************** Table: t2 Create Table: CREATE TABLE `t2` ( `id` binary(36) NOT NULL, `a` tinyint(3) unsigned NOT NULL, `v` varchar(512) DEFAULT NULL, PRIMARY KEY (`a`,`id`) /*T![clustered_index] CLUSTERED */ ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin 1 row in set (0.001 sec)
select * from information_schema.tikv_region_status where table_name='t2' limit 1\G
*************************** 1. row *************************** REGION_ID: 48 START_KEY: 7480000000000000FF3E5F720400000000FF0000000601633430FF3338646232FF2D64FF3531632D3131FF65FF622D386337352DFFFF3830653635303138FFFF61396265000000FF00FB000000000000F9 END_KEY: TABLE_ID: 62 DB_NAME: test TABLE_NAME: t2 IS_INDEX: 0 INDEX_ID: NULL INDEX_NAME: NULL EPOCH_CONF_VER: 1 EPOCH_VERSION: 38 WRITTEN_BYTES: 0 READ_BYTES: 0 APPROXIMATE_SIZE: 136 APPROXIMATE_KEYS: 479905 REPLICATIONSTATUS_STATE: NULL REPLICATIONSTATUS_STATEID: NULL 1 row in set (0.005 sec)
select tidb_decode_key('7480000000000000FF3E5F720400000000FF0000000601633430FF3338646232FF2D64FF3531632D3131FF65FF622D386337352DFFFF3830653635303138FFFF61396265000000FF00FB000000000000F9');
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | tidb_decode_key('7480000000000000FF3E5F720400000000FF0000000601633430FF3338646232FF2D64FF3531632D3131FF65FF622D386337352DFFFF3830653635303138FFFF61396265000000FF00FB000000000000F9') | +---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | {"handle":{"a":"6","id":"c4038db2-d51c-11eb-8c75-80e65018a9be"},"table_id":62} | +---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.001 sec)

TIDB_DECODE_PLAN

You can find TiDB execution plans in encoded form in the slow query log. The TIDB_DECODE_PLAN() function is then used to decode the encoded plans into a human-readable form.

This function is useful because a plan is captured at the time the statement is executed. Re-executing the statement in EXPLAIN might produce different results as data distribution and statistics evolves over time.

SELECT tidb_decode_plan('8QIYMAkzMV83CQEH8E85LjA0CWRhdGE6U2VsZWN0aW9uXzYJOTYwCXRpbWU6NzEzLjHCtXMsIGxvb3BzOjIsIGNvcF90YXNrOiB7bnVtOiAxLCBtYXg6IDU2OC41wgErRHByb2Nfa2V5czogMCwgcnBjXxEpAQwFWBAgNTQ5LglZyGNvcHJfY2FjaGVfaGl0X3JhdGlvOiAwLjAwfQkzLjk5IEtCCU4vQQoxCTFfNgkxXzAJMwm2SGx0KHRlc3QudC5hLCAxMDAwMCkNuQRrdgmiAHsFbBQzMTMuOMIBmQnEDDk2MH0BUgEEGAoyCTQzXzUFVwX1oGFibGU6dCwga2VlcCBvcmRlcjpmYWxzZSwgc3RhdHM6cHNldWRvCTk2ISE2aAAIMTUzXmYA')\G
*************************** 1. row *************************** tidb_decode_plan('8QIYMAkzMV83CQEH8E85LjA0CWRhdGE6U2VsZWN0aW9uXzYJOTYwCXRpbWU6NzEzLjHCtXMsIGxvb3BzOjIsIGNvcF90YXNrOiB7bnVtOiAxLCBtYXg6IDU2OC41wgErRHByb2Nfa2V5czogMCwgcnBjXxEpAQwFWBAgNTQ5LglZyGNvcHJfY2FjaGVfaGl0X3JhdGlvOiAwLjAwfQkzLjk5IEtCCU4vQQoxCTFfNgkxXz: id task estRows operator info actRows execution info memory disk TableReader_7 root 319.04 data:Selection_6 960 time:713.1µs, loops:2, cop_task: {num: 1, max: 568.5µs, proc_keys: 0, rpc_num: 1, rpc_time: 549.1µs, copr_cache_hit_ratio: 0.00} 3.99 KB N/A └─Selection_6 cop[tikv] 319.04 lt(test.t.a, 10000) 960 tikv_task:{time:313.8µs, loops:960} N/A N/A └─TableFullScan_5 cop[tikv] 960 table:t, keep order:false, stats:pseudo 960 tikv_task:{time:153µs, loops:960} N/A N/A

TIDB_PARSE_TSO

The TIDB_PARSE_TSO function can be used to extract the physical timestamp from a TiDB TSO timestamp. TSO stands for Time Stamp Oracle and is a monotonically increasing timestamp given out by PD (Placement Driver) for every transaction.

A TSO is a number that consists of two parts:

  • A physical timestamp
  • A logical counter
BEGIN; SELECT TIDB_PARSE_TSO(@@tidb_current_ts); ROLLBACK;
+-----------------------------------+ | TIDB_PARSE_TSO(@@tidb_current_ts) | +-----------------------------------+ | 2021-05-26 11:33:37.776000 | +-----------------------------------+ 1 row in set (0.0012 sec)

Here TIDB_PARSE_TSO is used to extract the physical timestamp from the timestamp number that is available in the tidb_current_ts session variable. Because timestamps are given out per transaction, this function is running in a transaction.

TIDB_VERSION

The TIDB_VERSION function can be used to get the version and build details of the TiDB server that you are connected to. You can use this function when reporting issues on GitHub.

SELECT TIDB_VERSION()\G
*************************** 1. row *************************** TIDB_VERSION(): Release Version: v5.1.0-alpha-13-gd5e0ed0aa-dirty Edition: Community Git Commit Hash: d5e0ed0aaed72d2f2dfe24e9deec31cb6cb5fdf0 Git Branch: master UTC Build Time: 2021-05-24 14:39:20 GoVersion: go1.13 Race Enabled: false TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306 Check Table Before Drop: false 1 row in set (0.00 sec)

MySQL compatibility

The TIDB_VERSION function is TiDB-specific and not compatible with MySQL. If MySQL compatibility is required, you can also use VERSION to get version information, but the result does not contain build details.

Was this page helpful?

Download PDFRequest docs changesAsk questions on Discord
Playground
One-stop & interactive experience of TiDB's capabilities WITHOUT registration.
Products
TiDB
TiDB Dedicated
TiDB Serverless
Pricing
Get Demo
Get Started
© 2024 PingCAP. All Rights Reserved.
Privacy Policy.