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https://issues.apache.org/jira/browse/ZOOKEEPER-2700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15876305#comment-15876305
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ASF GitHub Bot commented on ZOOKEEPER-2700:
-------------------------------------------

Github user flier commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/180#discussion_r102263924
  
    --- Diff: src/java/main/org/apache/zookeeper/server/ZooKeeperServer.java ---
    @@ -303,15 +305,38 @@ public void loadData() throws IOException, 
InterruptedException {
     
         public void takeSnapshot(){
    --- End diff --
    
    I have some scenes need to take snapshot, for example
    
    First, our major Zookeeper cluster was deployed in an AWS zone, some 
observers running at a dozen IDC. We use this topological structure because 
Zookeeper cluster is not friendly to multi-IDC deployment. Besize, our 
zookeeper snapshot and transaction logs are huge, because some wrong client 
usage that hard to fix in short time :(
    
    Sometimes, we plan to maintains the major cluster, we have to start another 
mirror cluster in same DC, and switch from the major cluster to the mirror 
cluster. If we do it faster enough, the observer and client will not concern 
the changes. That's why we need take snapshot to speed up the migration. If 
something got wrong, we could switch back to the old cluster, lost some 
transaction better than the whole system down.
    
    Second, our backup policy need a daily/hourly offline backup, to AWS S3 or 
other DC. I would like to take and upload a latest and clean snapshot, instead 
of tar an old snapshot with a number of transaction logs.
    
    Third, sometimes we need to deploy a new observer or a testing cluster in 
different DC, we have to copy the latest snapshot offline, because Zookeeper 
observer sync progress may become very slow, the TCP window could drop to 
10-20KB/s in the 40-60% packet loss rate.


> Force ZooKeeper to generate snapshot
> ------------------------------------
>
>                 Key: ZOOKEEPER-2700
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2700
>             Project: ZooKeeper
>          Issue Type: Improvement
>            Reporter: Flier Lu
>            Priority: Minor
>
> When cold backup or remote offline sync Zookeeper instances, we need the 
> latest snapshot.
> Add a four letter `snap` command to force Zookeeper to generate snapshot.



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