# Placement Driver
__*PD features*__
+ Metadata storage for the entire cluster TiKV
+ Assign Global **ID** and Transaction **ID**
+ Generate a global timestamp TSO
+ Collect cluster information for scheduling
+ Provide **TiDB Dashboard** service

![right](./student-guide/diagram/PD_en_001_20220506.png)

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We will introduce the main functions and implement principles of PD in detail. Let us take a brief look at its various functions.

1. Metadata storage for the entire cluster TiKV
Information such as region corresponding to key range and TiKV ( store ) where region (including information such as leader ) is located are stored in PD. For example, TiDB Server obtains routing information from PD and then accesses it to the relevant TiKV of the data.
In addition, the topological information of TiKV and the label (label) information are also stored in the PD, and will be explained in detail later.

2. Assigning a Global ID and a Transaction ID
The global ID we use, such as store ID, region ID, peer ID, table ID, index ID, etc., and the transaction ID of the distributed transaction are also assigned by PD.

3. Generating a global timestamp TSO 
TSO is a global timestamp used to guarantee the order of transaction in the database. A very important function of PD is to generate TSO. We will introduce the details later.

4. Collect cluster information for scheduling.
The TiKV node periodically reports the status of the cluster to PD. The PD is responsible for scheduling the region among TiKV nodes according to the relevant status. We will introduce the details later.

5. The TiDB Dashboard service is provided.