Symptoms

When starting up a JIRA node in Data Center, while other nodes are running, there is a large spike in network traffic between all currently running nodes.

Diagnosis

Reviewing network traffic indicates there are spikes on all nodes when a startup, or restart of one of the nodes occurs. For example Node A, B and C are running. When D is started, there are spikes of traffic on Nodes A, B, C & D.

Cause

JIRA Data Center uses a caching library called EHCache, and contains an in-memory cache of certain project, user and group data. On the very first node start (if no others are running) this cache is built from querying the database. When additional nodes are started, the cache is built from querying the existing nodes in-memory cache and propagating that data into the node that is starting up. Other caches are built only locally by filling the node's own copy of the cache directly from the database.

Additionally when JIRA Data Center restarts a node reindex thread runs which is designed to synchronise changes between the nodes - this can also contribute to the increase in network traffic.

Resolution

There is no resolution for this issue - it is expected behaviour of JIRA Data Center.