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Posted to dev@zookeeper.apache.org by "Fangmin Lv (JIRA)" <ji...@apache.org> on 2018/07/20 17:45:00 UTC
[jira] [Commented] (ZOOKEEPER-3086) [server] Lack of write timeouts
causes quorum to stuck
[ https://issues.apache.org/jira/browse/ZOOKEEPER-3086?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16551044#comment-16551044 ]
Fangmin Lv commented on ZOOKEEPER-3086:
---------------------------------------
[~elessar] thanks for reporting the issue, you mentioned at step 5, the follower blocks on Learner.ping forever due to the lack of write timeout, but in the follower/leader socket, we do set the timeout to be tickTime * syncLimit, it should timed out if we cannot send the ping within that time.
> [server] Lack of write timeouts causes quorum to stuck
> ------------------------------------------------------
>
> Key: ZOOKEEPER-3086
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3086
> Project: ZooKeeper
> Issue Type: Bug
> Components: quorum
> Affects Versions: 3.5.4, 3.4.12
> Environment: Linux 4.13.0-32-generic, Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)
> Reporter: Ruslan Nigmatullin
> Priority: Major
> Attachments: zookeeper-threads.txt
>
>
> Network outage on leader host can cause `QuorumPeer` thread to stuck for prolonged period of time (2+ hours, depends on tcp keep alive settings). It effectively stalls the whole zookeeper server making it inoperable. We've found it during one of our internal DRTs (Disaster Recovery Test).
> The scenario which triggers the behavior (requires relatively high ping-load to the follower):
> # `Follower.processPacket` processes `Leader.PING` message
> # Leader is network partitioned
> # `Learner.ping` makes attempt to write to the leader socket
> # If write socket buffer is full (due to other ping/sync calls) `Learner.ping` blocks
> # As leader is partitioned - `Learner.ping` blocks forever due to lack of write timeout
> # `QuorumPeer` is the only thread reading from the leader socket, effectively meaning that the whole server is stuck and can't recover without manual process restart.
>
> Thread dump from the affected server is in attachments.
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