# `Meta` Service
+ `TiKV Store` reports its status to `PD` periodically
  + Every 10 seconds by default via parameter **`raftstore.pd-store-heartbeat-tick-interval`**
+ `TiKV Region` reports its status to `PD` periodically
  + Every 60 seconds by default via parameter **`raftstore.pd-heartbeat-tick-interval`**
+ `Meta` data will be saved into `etcd` and `LevelDB`
  + `etcd` is used for availabilty
    + `Store/ID/TSO` meta information
  + `LevelDB` is used for effeiency
    + Region meta infomation
  + Region information update is in the `hot-path`
    + It is persistent in `TiKV` and can be obtained again through `TiKV`, so we use `LevelDB` to store it and sync between the `PD` nodes independently rather than using `etcd` to go through the `Raft` replication`
+ `ID Allocator` for `Store/Region/Peer ID` to make sure it is unique
+ `TSO Allocator` for `Percolator` transaction `StartTS` and `CommitTS`
+ Configuration persistence, etc ...

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