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- Glossary
RECOVER TABLE
RECOVER TABLE
is used to recover a deleted table and the data on it within the GC (Garbage Collection) life time after the DROP TABLE
statement is executed.
Syntax
RECOVER TABLE table_name
RECOVER TABLE BY JOB ddl_job_id
Synopsis
- RecoverTableStmt
- TableName
- Int64Num
- NUM
RecoverTableStmt ::=
'RECOVER' 'TABLE' ( 'BY' 'JOB' Int64Num | TableName Int64Num? )
TableName ::=
Identifier ( '.' Identifier )?
Int64Num ::= NUM
NUM ::= intLit
If a table is deleted and the GC lifetime is out, the table cannot be recovered with
RECOVER TABLE
. Execution ofRECOVER TABLE
in this scenario returns an error like:snapshot is older than GC safe point 2019-07-10 13:45:57 +0800 CST
.If the TiDB version is 3.0.0 or later, it is not recommended for you to use
RECOVER TABLE
when TiDB Binlog is used.RECOVER TABLE
is supported in the Binlog version 3.0.1, so you can useRECOVER TABLE
in the following three situations:- Binlog version is 3.0.1 or later.
- TiDB 3.0 is used both in the upstream cluster and the downstream cluster.
- The GC life time of the secondary cluster must be longer than that of the primary cluster. However, as latency occurs during data replication between upstream and downstream databases, data recovery might fail in the downstream.
Troubleshoot errors during TiDB Binlog replication
When you use RECOVER TABLE
in the upstream TiDB during TiDB Binlog replication, TiDB Binlog might be interrupted in the following three situations:
The downstream database does not support the
RECOVER TABLE
statement. An error instance:check the manual that corresponds to your MySQL server version for the right syntax to use near 'RECOVER TABLE table_name'
.The GC life time is not consistent between the upstream database and the downstream database. An error instance:
snapshot is older than GC safe point 2019-07-10 13:45:57 +0800 CST
.Latency occurs during replication between upstream and downstream databases. An error instance:
snapshot is older than GC safe point 2019-07-10 13:45:57 +0800 CST
.
For the above three situations, you can resume data replication from TiDB Binlog with a full import of the deleted table.
Examples
Recover the deleted table according to the table name.
DROP TABLE t;
RECOVER TABLE t;
This method searches the recent DDL job history and locates the first DDL operation of the
DROP TABLE
type, and then recovers the deleted table with the name identical to the one table name specified in theRECOVER TABLE
statement.Recover the deleted table according to the table's
DDL JOB ID
used.Suppose that you had deleted the table
t
and created anothert
, and again you deleted the newly createdt
. Then, if you want to recover thet
deleted in the first place, you must use the method that specifies theDDL JOB ID
.DROP TABLE t;
ADMIN SHOW DDL JOBS 1;
The second statement above is used to search for the table's
DDL JOB ID
to deletet
. In the following example, the ID is53
.+--------+---------+------------+------------+--------------+-----------+----------+-----------+-----------------------------------+--------+ | JOB_ID | DB_NAME | TABLE_NAME | JOB_TYPE | SCHEMA_STATE | SCHEMA_ID | TABLE_ID | ROW_COUNT | START_TIME | STATE | +--------+---------+------------+------------+--------------+-----------+----------+-----------+-----------------------------------+--------+ | 53 | test | | drop table | none | 1 | 41 | 0 | 2019-07-10 13:23:18.277 +0800 CST | synced | +--------+---------+------------+------------+--------------+-----------+----------+-----------+-----------------------------------+--------+
RECOVER TABLE BY JOB 53;
This method recovers the deleted table via the
DDL JOB ID
. If the corresponding DDL job is not of theDROP TABLE
type, an error occurs.
Implementation principle
When deleting a table, TiDB only deletes the table metadata, and writes the table data (row data and index data) to be deleted to the mysql.gc_delete_range
table. The GC Worker in the TiDB background periodically removes from the mysql.gc_delete_range
table the keys that exceed the GC life time.
Therefore, to recover a table, you only need to recover the table metadata and delete the corresponding row record in the mysql.gc_delete_range
table before the GC Worker deletes the table data. You can use a snapshot read of TiDB to recover the table metadata. Refer to Read Historical Data for details.
Table recovery is done by TiDB obtaining the table metadata through snapshot read, and then going through the process of table creation similar to CREATE TABLE
. Therefore, RECOVER TABLE
itself is, in essence, a kind of DDL operation.
MySQL compatibility
This statement is a TiDB extension to MySQL syntax.