Resource relationships

The main entity used in Managed Service for Greenplum® is a database cluster.

Each cluster consists of database hosts, which are virtual machines with DBMS servers deployed on them. A Managed Service for Greenplum® cluster contains:

• Two master hosts.
• Two or more segment hosts.

The primary master host (PRIMARY) accepts client connections and SQL queries and distributes them to the segment hosts for processing.

The standby master host (STANDBY) continuously replicates the primary one's data but accepts no user connections.

If the primary master fails, the standby one takes over. This way, a cluster with two master hosts continues handling queries if a single master fails.

Segment hosts have standalone DBMS's (segments) deployed on them. They store data fragments and perform most operations for handling queries. Each cluster segment has a replica, i.e., a mirror segment that is located on another host and stores a copy of the data from the main segment.

The number of segments is the same for each host. When expanding a cluster, you can increase the number of segments. They will be added to all hosts — both new and existing ones. You cannot add segments to existing hosts without expanding the cluster.

VMs for cluster hosts can be hosted on:

• Regular Yandex Cloud hosts:

  These are physical servers for hosting cluster VMs. They are randomly selected from a pool of available hosts that meet the selected cluster configuration.

• Dedicated Yandex Cloud hosts:

  These are physical servers that only host your VMs. VMs on dedicated hosts have all features of regular VMs; additionally, they are physically isolated from other users' VMs.

  Dedicated hosts are selected from dedicated host groups specified when creating a cluster.

  For more information, see Dedicated hosts.

When creating a cluster, specify:

• Host class: Template for deploying cluster hosts. For a list of available host classes and their characteristics, see Host classes.

• Environment: Environment where the cluster will be deployed:

  • PRODUCTION: For stable versions of your apps.
  • PRESTABLE: For testing purposes. The prestable environment is similar to the production environment and likewise covered by the SLA, but it is the first to get new functionalities, improvements, and bug fixes. In the prestable environment, you can test compatibility of new versions with your application.

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