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https://issues.apache.org/jira/browse/BOOKKEEPER-564?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13633678#comment-13633678
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Sijie Guo commented on BOOKKEEPER-564:
--------------------------------------

{quote}
This is control coupling. It makes LedgerStorage dependent on the behaviour of 
SyncThread and makes it impossible to reason about or test the LedgerStorage in 
isolation.
{quote}

How it worked in previous flow on testing LedgerStorage in isolation? I don't 
quite understand about this part.

{quote}
What actually happens is that the ledger storage is saying "hey, checkpoint to 
this point now!"
{quote}

in previous flow, sync thread just checkpoint blindly. in current flow, ledger 
storage would tell the syncthread (the checkpointer) the point which is a 
better point to do checkpoint. the only thing that ledger storage gave out is 
the point to guide checkpoint. but if you mean the guide is coupling, I have 
nothing more to say.
                
> Better checkpoint mechanism
> ---------------------------
>
>                 Key: BOOKKEEPER-564
>                 URL: https://issues.apache.org/jira/browse/BOOKKEEPER-564
>             Project: Bookkeeper
>          Issue Type: Improvement
>          Components: bookkeeper-server
>            Reporter: Sijie Guo
>            Assignee: Sijie Guo
>             Fix For: 4.3.0
>
>         Attachments: 0001-BOOKKEEPER-564-Better-checkpoint-mechanism.patch, 
> 0001-BOOKKEEPER-564-Better-checkpoint-mechanism.patch, 
> 0002-BOOKKEEPER-564-Better-checkpoint-mechanism.patch, BOOKKEEPER-564.patch, 
> BOOKKEEPER-564.patch
>
>
> Currently, SyncThread made a checkpoint too frequently, which affects 
> performance. data is writing to entry logger file might be blocked by syncing 
> same entry logger file, which affect bookie to achieve higher throughput. We 
> could schedule checkpoint only when rotating an entry log file. so new 
> incoming entries would be written to newer entry log file and old entry log 
> file could be synced.

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