Lin Changrui created ZOOKEEPER-4306:
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Summary: CloseSessionTxn contains too many ephemal nodes cause
cluster crash
Key: ZOOKEEPER-4306
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-4306
Project: ZooKeeper
Issue Type: Bug
Affects Versions: 3.6.2
Reporter: Lin Changrui
Attachments: cs.jpg, f.jpg, l1.png, l2.jpg, r.jpg
We took a test about how many ephemal nodes can client create under one parent
node with defalut configuration. The test caused cluster crash at last,
exception stack trace like this.
follower:
!f.jpg!
leader:
!l1.png!
!l2.jpg!
It seems that leader sent a too large txn packet to followers. When follower
try to deserialize the txn, it found the txn length out of its buffer
size(default 1MB+1MB, jute.maxbuffer + jute.maxbuffer.extrasize). That causes
followers crashed, and then, leader found there was no sufficient followers
synced, so leader shutdown later. When leader shutdown, it called
zkDb.fastForwardDataBase() , and leader found the txn read from txnlog out of
its buffer size, so it crashed too.
After the servers crashed, they try to restart the quorum. But they would not
success because the last txn is too large. We lose the log at that moment, but
the stack trace is same as this one.
!r.jpg|width=1468,height=598!
*Root Cause*
We use org.apache.zookeeper.server.LogFormatter(-Djute.maxbuffer=74827780)
visualize this log and found this. !cs.jpg|width=1400,height=581! So
closeSessionTxn contains all ephemal nodes with absolute path. We know we will
get a large getChildren respose if we create too many children nodes under one
parent node, that is limited by jute.maxbuffer of client. If we create plenty
of ephemal nodes under different parent nodes with one session, it may not
cause out of buffer of client, but when the session close without delete these
node first, it probably cause cluster crash.
Is it a bug or just a unspecified feature？If it just so, how should we judge
the upper limit of creating nodes?
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