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https://issues.apache.org/jira/browse/BOOKKEEPER-879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15027717#comment-15027717
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Matteo Merli commented on BOOKKEEPER-879:
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I have a couple of concerns on the pull request:
# If we record "ctime", it might be useful to expose other informations that
can be currently get from the z-node stats, like the last modification
timestamp "mtime" and how many changes there were on the ledger metadata
(z-node version)
# When this feature is introduced, older ledger will not have the "ctime"
field. What should I expect to get in that case? How would I know whether a
ledger was created before or after the feature was rolled out? (This can also
be at different times for different hosts) Can we fallback to z-node
information if the field is not there?
# We need to ensure that older clients are able to de-serialize the message
metadata correctly (In the past I've seen errors with protocol buffer text
format when new field are introduced)
Lastly, I don't think the ZK backup/restore is a very compelling reason to add
this feature because:
# you cannot backup z-node one by one because that will lead to inconsistencies
# to backup your ZK data, you simply need to copy the last ZK snapshot and
transaction log
# to restore from snaphot, you need to shutdown your ZK quorum, copy the
snapshot and txn log to all participants and restart the quorum
# after the restore, all z-nodes will have the correct ctime, mtime, etc. :)
> Record ledger creation time
> ---------------------------
>
> Key: BOOKKEEPER-879
> URL: https://issues.apache.org/jira/browse/BOOKKEEPER-879
> Project: Bookkeeper
> Issue Type: New Feature
> Components: bookkeeper-client, bookkeeper-server
> Affects Versions: 4.3.1
> Reporter: Enrico Olivelli
>
> I think that a creation timestamp would be very useful and it does not cost
> very much. It would be an immutable value.
> Nowadays (on 4.3.1) I must keep that info together with the id of the ledger,
> for instance in zookeeper, but if that reference gets lost there is now way
> to know how old a ledger is.
> I think that this timestamp should be captured on client while calling
> createLedger or asyncCreateLedger.
> In addition to this very common field maybe it would be useful to add a
> custom byte[] field named "custom client data" in order to let the client
> 'describe' the ledger without the need of extra data on Zookeeper.
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