Cluster

The web interface differs for cluster deployments and single-server instances. Instead of a single Dashboard, there is a CLUSTER and a NODES section.

Furthermore, the REPLICATION and LOGS section are not available. You can access the logs of individual Coordinators and DB-Servers via the NODES section.

Cluster

The CLUSTER section displays statistics about the general cluster performance.

Web Interface Cluster Dashboard

Statistics:

  • Available and missing Coordinators
  • Available and missing DB-Servers
  • Memory usage (percent)
  • Current connections
  • Data (bytes)
  • HTTP (bytes)
  • Average request time (seconds)

Distribution:

  • Number of databases and collections
  • Number of shards, leader shards, follower shards etc.
  • Shard distribution
  • Shard rebalancing

Maintenance:

  • Toggle the cluster supervision maintenance mode

Shard rebalancing

Over time, imbalances in the data distribution and shard leaders and followers can occur in clusters. You can manually trigger a rebalancing operation to achieve a more even distribution.

A new DB-Server does not have any shards. With the rebalance functionality, the cluster starts to rebalance shards including empty DB-Servers. You can specify the maximum number of shards that can be moved in each operation by using the --cluster.max-number-of-move-shards startup option of arangod.

You can set the following options:

  • Move Leaders
  • Move Followers
  • Include System Collections

When you click the Rebalance button, the number of scheduled move shards operations is shown, or it is displayed that no move operations have been scheduled if they are not necessary.

Nodes

The NODES section provides an overview over the cluster nodes and a way to access information about the individual Coordinators and DB-Servers.

Overview

The Overview tab shows available and missing Coordinators and DB-Servers.

Functions:

  • Coordinator Dashboard: Click a Coordinator to open a statistics dashboard.

Information (Coordinator / DB-Servers):

  • Name
  • Endpoint
  • Last Heartbeat
  • Status
  • Health

Shards

The Shards tab displays all available sharded collections, their leaders and followers.

To move a shard leader or follower to a different DB-Server, click one of the Leader or Followers entries to open a move shard dialog.

The leadership of a shard can be transferred to all available DB-Servers except the current leading DB-Server.

You can move a follower to a different DB-Server if it is available and neither the leading DB-Server or the following DB-Server itself.

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