[ZOOKEEPER-2899] Zookeeper not receiving packets after ZXID overflows

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.4.5
• Component/s: leaderElection

Environment

5 host ensemble, 1500+ client connections each, 300K+ nodes
OS: Ubuntu precise
JAVA 7
JuniperQFX510048T NIC, 10000Mb/s, ixgbe driver
6 core Intel(R)Xeon(R)_CPU_E5-2620_v3@_2.40GHz
4 HDD 600G each

• Assignee: Unassigned
• Reporter: Yicheng Fang
• Created: 15/Sep/17 01:00
• Updated: 05/Oct/17 18:18

Description

ZK was used with Kafka (version 0.10.0) for coordination. We had a lot of Kafka consumers writing consumption offsets to ZK.

We observed the issue two times within the last year. Each time after ZXID overflowed, ZK was not receiving packets even though leader election looked successful from the logs, and ZK servers were up. As a result, the whole Kafka system came to a halt.

As an attempt to reproduce (and hopefully fixing) the issue, I set up test ZK and Kafka clusters and feed them with like-production test traffic. Though not really able to reproduce the issue, I did see that the Kafka consumers, which used ZK clients, essentially DOSed the ensemble, filling up the `submittedRequests` in `PrepRequestProcessor`, causing even 100ms+ read latencies.

More details are included in the comments.