Slow Kanban response and performance after upgrade to Jira 6.4

Summary

Jira 6.4 instance is responding slowly in many screens, with some screens showing timeouts.

Environment

Large instance with many swimlanes or card colours configured for the Agile Kanban board

Expected Results

It works with acceptable performance (20-30 sec).

Actual Results

It works slow (> 30 sec).

Notes

Cause

Cause is boards with many swimlanes and card colours.

For every card colour or swimlane that is defined using JQL, the entire board query is run again, with the additional JQL appended. So if no swimlanes or card colours are defined and the board opens in N seconds, each swimlane or card colour defined is guaranteed to increase the load time by at least another N seconds. Given 5 swimlanes + 2 card colours + the actual board query, this board will take at least 8*N seconds to open.

2 Problems:

1. For the customer's instance: "N" is large (lucene is not performant)
2. We're running a lot of queries each time we display the board.

Workaround

Remove swimlanes or card colours from the configuration.
Please check KB article: Kanban board loading is slow - performance problems