[ZOOKEEPER-3169] Reduce session revalidation time after zxid roll over

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.4.5, 3.5.0
• Fix Version/s: 3.4.5
• Flags: Important
• Assignee: Unassigned
• Reporter: 田毅群
• Created: 13/Oct/18 14:32
• Updated: 04/Nov/18 11:51

Description

1. Sometimes Zookeeper cluster will receive a lot of connections from clients, sometimes connection number even exceeds 1W. When zxid rolls over, the clients will reconnect and revalidate the session.

2. In Zookeeper design structure, when follower server receives the session revalidation requests, it will send requests to leader server, which is designed to be responsible for session revalidation.

3. In a short time, Leader will handle lots of requests. I use a tool to get the statistics, some clients need to wait over 20s. It is too long for some special clients, like ResourceManager.

4. I design a thought: when zxid rollover happens. Leader will record the accurate time. When reelection finishs, all servers will get the rollover time. When clients reconnect and revalidate session. All servers can judge it. So it can reduce a lots of pressure of cluster, all clients can will wait for less time.

Issue Links

• links to: GitHub Pull Request #688