TiKV shards continuous ranges of keys into Regions, and replicates Regions via the Raft protocol. When data size increases until reaching a threshold, a Region will be split into multiple. Conversely, if the size of the Region shrinks due to data deletion, two adjacent Regions can be merged into one.

Region Merge

The Region Merge process is initiated by the PD. The steps are:

1. PD polls the Regions’ status by the interval.

2. Ensure all replicas of the two Regions to be merged must be stored on the same set of TiKV(s).

3. If the two adjacent regions’ sizes are both less than max-merge-region-size and the numbers of keys within the regions are both less than max-merge-region-keys, PD will start the Region Merge process that merges the bigger region into the smaller region.

Configure Region Merge

You can use pd-ctl or the PD configuration file to configure Region Merge.

Region Merge is enabled by default. To disable Region Merge, set the following parameters to a zero:

• max-merge-region-size
• max-merge-region-keys

• merge-schedule-limit

• Newly split Regions won’t be merged within the period of time specified by split-merge-interval.

• Region Merge won’t happen within the period of time specified by split-merge-interval after PD starts or restarts.

You can find all other configuration options for scheduling here.