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Maintain a TiFlash Cluster

This document describes how to perform common operations when you maintain a TiFlash cluster, including checking the TiFlash version. This document also introduces critical logs and a system table of TiFlash.

Check the TiFlash version

There are two ways to check the TiFlash version:

If the binary file name of TiFlash is tiflash, you can check the version by executing the ./tiflash version command.
However, to execute the above command, you need to add the directory path which includes the libtiflash_proxy.so dynamic library to the LD_LIBRARY_PATH environment variable. This is because the running of TiFlash relies on the libtiflash_proxy.so dynamic library.
For example, when tiflash and libtiflash_proxy.so are in the same directory, you can first switch to this directory, and then use the following command to check the TiFlash version:
```
LD_LIBRARY_PATH=./ ./tiflash version
```
Check the TiFlash version by referring to the TiFlash log. For the log path, see the [logger] part in the tiflash.toml file. For example:
```
<information>: TiFlash version: TiFlash 0.2.0 master-375035282451103999f3863c691e2fc2
```

TiFlash critical logs

Log Information	Log Description
`[INFO] [<unknown>] ["KVStore: Start to persist [region 47, applied: term 6 index 10]"] [thread_id=23]`	Data starts to be replicated (the number in the square brackets at the start of the log refers to the thread ID
`[DEBUG] [<unknown>] ["CoprocessorHandler: grpc::Status DB::CoprocessorHandler::execute(): Handling DAG request"] [thread_id=30]`	Handling DAG request, that is, TiFlash starts to handle a Coprocessor request
`[DEBUG] [<unknown>] ["CoprocessorHandler: grpc::Status DB::CoprocessorHandler::execute(): Handle DAG request done"] [thread_id=30]`	Handling DAG request done, that is, TiFlash finishes handling a Coprocessor request

You can find the beginning or the end of a Coprocessor request, and then locate the related logs of the Coprocessor request through the thread ID printed at the start of the log.

TiFlash system table

The column names and their descriptions of the information_schema.tiflash_replica system table are as follows:

Column Name	Description
TABLE_SCHEMA	Database name
TABLE_NAME	Table name
TABLE_ID	Table ID
REPLICA_COUNT	Number of TiFlash replicas
LOCATION_LABELS	The hint for PD, based on which multiple replicas in a Region are scattered
AVAILABLE	Available or not (0/1)
PROGRESS	Replication progress [0.0~1.0]