Datacenters and racks

Each data broker belongs to a datacenter and a rack. You give both when you declare the data broker (create databroker ... DATACENTER RACK) or in the DATA_BROKER line of the installation file.

Datacenters

A table is deployed in one datacenter, that you name before the deployment:

alter table orders set datacenter 'DC1';

There is no default. show datacenters; lists the datacenters of the cluster, and show databrokers; the data brokers.

Racks

A rack is a group of data brokers that can fail together (the same power supply, the same switch). When a table has two or three copies, SynSQL places each copy in a different rack of the datacenter. The first copy goes to the rack with the most data brokers.

This has two consequences:

• the number of partitions of a table with several copies is limited by the size of the biggest rack, not by the total number of data brokers;
• the deployment fails if the datacenter does not have enough racks or enough data brokers for the number of copies you asked.

For a table with one copy, racks do not matter.

The affinity column

The DATA_BROKER lines of the installation file have a last column, affinity. The sample file uses *. Leave it unless your support tells you otherwise.