[jira] [Commented] (BOOKKEEPER-249) Revisit garbage collection algorithm in Bookie server

["Rakesh R (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/BOOKKEEPER-249?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13496903#comment-13496903 ] 

Rakesh R commented on BOOKKEEPER-249:
-------------------------------------

Hi Sijie, The idea of having DELETED state is nice and avoids unnecesary GC passes.

{quote}
Even we restricted deletion semantic above, we would still encountering zombie entries when changing ensemble
(it would happen during bookie failures and auto-rereplication).
{quote}

Re-replication of an OPEN ledger:-
For the above concern, if there is a bk failure in the writing ensemble, auto-rereplication process would wait for the defined grace period and initiate fence the ledger. Only after successful fencing would continue with re-replication of the ledger to new bookie. So the writer would get exception when tries writing later and prevents zombie entries.

Re-replication of CLOSED ledger:-
Here, the auto-rereplication would results zombie entries due to ensemble change. In your proposal I understand there is a place to hold all the ledgers to be deleted in ledgerManager, we could use that and just add one more step in autorereplication logic to update these failed bookie's ledgers in 'ledgers/deleted/Bi/'. So later once the failed bookie comes back, will do GCing. Also, we could think of using zk multi-transaction apis if there is any problem with zkDisconnection while updating failed bookie to new bookie(ledger's ensemble) and updating deleted ledgers of failed bookie.

Whats your opinion, Sijie?
                
> Revisit garbage collection algorithm in Bookie server
> -----------------------------------------------------
>
>                 Key: BOOKKEEPER-249
>                 URL: https://issues.apache.org/jira/browse/BOOKKEEPER-249
>             Project: Bookkeeper
>          Issue Type: Improvement
>          Components: bookkeeper-server
>            Reporter: Sijie Guo
>             Fix For: 4.2.0
>
>         Attachments: gc_revisit.pdf
>
>
> Per discussion in BOOKKEEPER-181, it would be better to revisit garbage collection algorithm in bookie server. so create a subtask to focus on it.

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