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https://issues.apache.org/jira/browse/ZOOKEEPER-4253?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17341634#comment-17341634
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Damon Liu commented on ZOOKEEPER-4253:
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Can someone explain the possible reasons for this？
> The client connects to zookeeper twice and get the same session id
> ------------------------------------------------------------------
>
> Key: ZOOKEEPER-4253
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-4253
> Project: ZooKeeper
> Issue Type: Bug
> Affects Versions: 3.4.13
> Reporter: Damon Liu
> Priority: Major
> Attachments: AA.log, BB.log, zookeeper.log
>
>
> App AA connects to ZooKeeper and creates a temporary path such as
> /brokers/ids/10. Another APP BB also connects to ZooKeeper. At some point AA
> BB and ZooKeeper are restarted, and BB allocates AA's old session
> before restart:
> AA connect to zookeeper ,and log in zk:
> [2021-03-07 08:47:43,468] INFO [SyncThread:0] Established session
> {color:#ff0000}0x10000053ef90000{color} with negotiated timeout 8000 for
> client /{color:#ff0000}22.20.0.45{color}:59966
> (org.apache.zookeeper.server.ZooKeeperServer)
>
> after restart:
> BB connect to zookeeper ,and log in zk:
> [2021-03-07 08:58:51,351] INFO [SyncThread:0] Established session
> {color:#ff0000}0x10000053ef90000{color} with negotiated timeout 30000 for
> client /{color:#ff0000}22.20.0.47{color}:39360
> (org.apache.zookeeper.server.ZooKeeperServer)
>
> I understand that after a restart, ZooKeeper loads old transaction logs and
> snapshot files, and old sessions and temporary paths are loaded. If BB
> obtains the old session 0x10000053ef90000 at this point, the session will not
> expire and the temporary path will not be deleted, causing AA to be unable to
> re-register the temporary path
> This is my question. I look forward to your help. Thank you very much!
>
> 2021/03/17 14:44
> I have checked the source code of zookeeper, and the generation of session is
> as follows:
> {code:java}
> public static long initializeNextSession(long id) {
> long nextSid = 0;
> nextSid = (Time.currentElapsedTime() << 24) >>> 8;
> nextSid = nextSid | (id <<56);
> return nextSid;
> }{code}
> Id is a fixed value, and the only variable that affects session id is the
> current time. Obviously zookeeper it takes different time to create session
> twice, but why get the same session id?
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