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https://issues.apache.org/jira/browse/HDFS-1580?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13039766#comment-13039766
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Ivan Kelly commented on HDFS-1580:
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{quote}Would it be better instead to ask getHighestTxid()?{quote}
#getNumberOfTransactions() is useful for deciding which journal to use.
Presumably sinceTxnId refers to the last transaction Id loaded from the image.
So sinceTxnId + getNumberOfTransactions() gives you the maximum prefix of the
NameNode history a particular journal can give you.
#getHighestTxid() would, however, give you the highest transaction id without
taking into consideration that gaps may exist.
> Add interface for generic Write Ahead Logging mechanisms
> --------------------------------------------------------
>
> Key: HDFS-1580
> URL: https://issues.apache.org/jira/browse/HDFS-1580
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Ivan Kelly
> Fix For: Edit log branch (HDFS-1073)
>
> Attachments: EditlogInterface.1.pdf, EditlogInterface.2.pdf,
> HDFS-1580+1521.diff, HDFS-1580.diff, HDFS-1580.diff, HDFS-1580.diff,
> generic_wal_iface.pdf, generic_wal_iface.pdf, generic_wal_iface.pdf,
> generic_wal_iface.txt
>
>
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