pbm-agent

A pbm-agent is a process that runs backup, restore, delete, and other operations available with Percona Backup for MongoDB.

A pbm-agent instance must run for every mongod instance that is not an arbiter node. This includes replica set nodes that are currently secondaries and config server replica set nodes in a sharded cluster.

An operation is triggered when the pbm CLI makes an update to the PBM Control collection. All pbm-agents monitor changes to the PBM control collections, but only one pbm-agent in each replica set will be elected to execute an operation. The elections are done by a random choice among secondary nodes. If no secondary nodes respond, then the pbm-agent on the primary node is elected for an operation.

The elected pbm-agent acquires a lock for an operation. This prevents mutually exclusive operations like backup and restore to be executed simultaneously.

Nomination and election process within PBM

If the pbm-agent running on the primary node of the replica set or on the primary node of the config replica set fails, the backup will not start as these agents are responsible for internal nomination process. You must therefore ensure that all the pbm-agent processes are up and running.

When the operation is complete, the pbm-agent releases the lock and updates the PBM control collections.

A single pbm-agent is involved with only one cluster (or non-sharded replica set). The pbm CLI utility can connect to any cluster to which it has network access, so it is possible for one user to list and launch backups or restores on many clusters.

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Last update: October 2, 2024
Created: October 2, 2024