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https://issues.apache.org/jira/browse/BOOKKEEPER-590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13625105#comment-13625105
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Jiannan Wang commented on BOOKKEEPER-590:
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Sure, that's Ok. But after ledger id space is enlarged from 32bits to 64bits,
the original scan-and-compare gc implementation may encounter the order issue
for MSLedgerManager. Then is it necessary to maintain the original
implementation? I may take it as a burden :)
> Another Scan-And-Compare GC Implementation
> ------------------------------------------
>
> Key: BOOKKEEPER-590
> URL: https://issues.apache.org/jira/browse/BOOKKEEPER-590
> Project: Bookkeeper
> Issue Type: Improvement
> Components: bookkeeper-server
> Reporter: Jiannan Wang
> Assignee: Jiannan Wang
> Attachments: BOOKKEEPER-590.patch
>
>
> The idea of Scan-And-Compare GC is as below:
> * Assume the ledger id list in local bookie server is *LocalLedgers*
> * At the same time, the ledger id list at metadata storage is *LiveLedgers*
> * Then the ledgers require garbage collection are *LocalLedgers -
> LiveLedgers*
> Under current implementation, an ledger id order guarantee is required when
> obtain *LiveLedgers* from metadata storage. However, this is unnecessary: we
> get *LocalLedgers* and we can just remove elements that in *LiveLedgers* one
> by one in any order.
> What's more, without the order requirement when scan all ledger ids, some
> things become simple:
> * We even don't need radix tree to maintain 64-bits ledger metadata, a
> hierarchical hash tree is enough (just as what topic metadata management
> does).
> * Easy to handle 64-bit ledger id backward compatibility for
> MSLedgerManager:
> ** Currently, for MSLedgerManager, we format ledger id to a fixed
> length (it's 10 now) digit string to make order scan
> ** When a 64-bit ledger id is used we need to enlarge the fixed length,
> then old ledger id backward compatibility turns to be a trouble if we require
> this order guarantee.
> As above reasons, it would better to remove specific order requirement from
> current Scan-And-Compare GC implementation.
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