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Data Check for TiDB Upstream and Downstream Clusters

You can use TiDB Binlog to build upstream and downstream clusters of TiDB. When Drainer replicates data to TiDB, the checkpoint is saved and the TSO mapping relationship between the upstream and downstream is also saved as ts-map. To check data between the upstream and downstream, configure snapshot in sync-diff-inspector.

Step 1: obtain ts-map

To obtain ts-map, execute the following SQL statement in the downstream TiDB cluster:

mysql> select * from tidb_binlog.checkpoint;
+---------------------+---------------------------------------------------------------------------------------------------------+
| clusterID           | checkPoint                                                                                              |
+---------------------+---------------------------------------------------------------------------------------------------------+
| 6711243465327639221 | {"commitTS":409622383615541249,"ts-map":{"primary-ts":409621863377928194,"secondary-ts":409621863377928345}} |
+---------------------+---------------------------------------------------------------------------------------------------------+

Step 2: configure snapshot

Then configure the snapshot information of the upstream and downstream databases by using the ts-map information obtained in Step 1.

Here is a configuration example of the Databases config section:

######################### Databases config #########################

# Configuration of the source database instance
[[source-db]]
    host = "127.0.0.1"
    port = 4000
    user = "root"
    password = "123456"
    # The instance ID of the source database, the unique identifier of a database instance
    instance-id = "source-1"
    # Uses the snapshot function of TiDB, corresponding to the primary-ts in ts-map
    snapshot = "409621863377928194"

# Configuration of the target database instance
[target-db]
    host = "127.0.0.1"
    port = 4001
    user = "root"
    password = "123456"
    # Uses the snapshot function of TiDB, corresponding to the secondary-ts in ts-map
    snapshot = "409621863377928345"

Note:

  • Set db-type of Drainer to tidb to ensure that ts-map is saved in the checkpoint.
  • Modify the Garbage Collection (GC) time of TiKV to ensure that the historical data corresponding to snapshot is not collected by GC during the data check. It is recommended that you modify the GC time to 1 hour and recover the setting after the check.
  • In some versions of TiDB Binlog, master-ts and slave-ts are stored in ts-map. master-ts is equivalent to primary-ts and slave-ts is equivalent to secondary-ts.
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