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https://issues.apache.org/jira/browse/HBASE-8741?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13688757#comment-13688757
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Himanshu Vashishtha commented on HBASE-8741:
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Hmmm, this idea does make sense to me.
So, a wal file will have sequenceId from bunch of regions, and its sequenceId
will not be in ascending order. But, that shouldn't be any problem. In case of
multi wals, it should also work.
[~sershe]: Why do you think it will complicate log cleanup? It seems that the
current replay/splitting should be able to digest it too, with minimal change.
The only change I could see is passing some context info about maximum possible
number of entries a region could have, while opening it to a new region server.
We could use Enis way of having maximum number of entries per wal (as Stack
suggested), or a hint based on the size of wal file.
> Mutations on Regions in recovery mode might have same sequenceIDs
> -----------------------------------------------------------------
>
> Key: HBASE-8741
> URL: https://issues.apache.org/jira/browse/HBASE-8741
> Project: HBase
> Issue Type: Bug
> Components: MTTR
> Affects Versions: 0.95.1
> Reporter: Himanshu Vashishtha
> Assignee: Himanshu Vashishtha
>
> Currently, when opening a region, we find the maximum sequence ID from all
> its HFiles and then set the LogSequenceId of the log (in case the later is at
> a small value). This works good in recovered.edits case as we are not writing
> to the region until we have replayed all of its previous edits.
> With distributed log replay, if we want to enable writes while a region is
> under recovery, we need to make sure that the logSequenceId > maximum
> logSequenceId of the old regionserver. Otherwise, we might have a situation
> where new edits have same (or smaller) sequenceIds.
> We can store region level information in the WALTrailer, than this scenario
> could be avoided by:
> a) reading the trailer of the "last completed" file, i.e., last wal file
> which has a trailer and,
> b) completely reading the last wal file (this file would not have the
> trailer, so it needs to be read completely).
> In future, if we switch to multi wal file, we could read the trailer for all
> completed WAL files, and reading the remaining incomplete files.
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