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Back Up and Restore Databend Meta Service Cluster

This guideline will introduce how to back up and restore the meta service cluster data.

Export Data From Meta Service​

Shutdown the databend-meta service.

Then export sled DB from the dir(<your_meta_dir>) in which the databend-meta stores meta to a local file output_fn, in multi-line JSON format. E.g., every line in the output file is a JSON of an exported key-value record.

# cargo build --bin databend-metactl

./target/debug/databend-metactl --export --raft-dir "<your_meta_dir>" > --db <output_fn>

# tail "<output_fn>"
# ["state_machine/0",{"Nodes":{"key":2,"value":{"name":"","endpoint":{"addr":"localhost","port":28203}}}}]
# ["state_machine/0",{"Nodes":{"key":3,"value":{"name":"","endpoint":{"addr":"localhost","port":28303}}}}]
# ["state_machine/0",{"StateMachineMeta":{"key":"LastApplied","value":{"LogId":{"term":1,"index":378}}}}]
# ["state_machine/0",{"StateMachineMeta":{"key":"Initialized","value":{"Bool":true}}}]
# ...

Note: without the --db argument, the exported data will output to the stdio instead.

Restore a databend-meta​

The following command rebuild a meta service db in <your_meta_dir> from exported metadata:

./target/debug/databend-metactl --import --raft-dir "<your_meta_dir>" --db <output_fn>

databend-meta --raft-dir "<your_meta_dir>" ...

Note: without the --db argument, the import data come from stdio instead, like:

cat "<output_fn>" | ./target/debug/databend-metactl --import --raft-dir "<your_meta_dir>"

Caveat: Data in <your_meta_dir> will be cleared.

Import data as a new databend-meta cluster​

With specifies the --initial-cluster argument, the databend-metactl can import the data as a new cluster. The --initial-cluster format is: node_id=raft_advertise_host:raft_api_port,grpc_api_addr, each node config is separated by space, the meaning of raft_advertise_host,raft_api_port,grpc_api_addr is the same in raft config.

E.g.:

/target/debug/databend-metactl --import --raft-dir ./.databend/new_meta1 --id=1 --db meta.db --initial-cluster 1=localhost:29103,0.0.0.0:19191 2=localhost:29203,0.0.0.0:29191 3=localhost:29303,0.0.0.0:39191
/target/debug/databend-metactl --import --raft-dir ./.databend/new_meta2 --id=2 --db meta.db --initial-cluster 1=localhost:29103,0.0.0.0:19191 2=localhost:29203,0.0.0.0:29191 3=localhost:29303,0.0.0.0:39191
/target/debug/databend-metactl --import --raft-dir ./.databend/new_meta3 --id=3 --db meta.db --initial-cluster 1=localhost:29103,0.0.0.0:19191 2=localhost:29203,0.0.0.0:29191 3=localhost:29303,0.0.0.0:39191

The script above imports the exported data from meta.db and initializes the three cluster nodes: id 1, which raft directory is ./.databend/new_meta1, and so are id 2 and 3 with different raft directory. Note that the --initial-cluster argument in these three command line is the same.

After that, can start a new three nodes databend-meta cluster with the new config and imported data.