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https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13402416#comment-13402416
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Andy Isaacson commented on HDFS-3077:
-------------------------------------
{code}
+ public static long readFile(File file, long defaultVal) throws IOException {
+ long val = defaultVal;
+ if (file.exists()) {
+ BufferedReader br = new BufferedReader(new FileReader(file));
{code}
This suffers from a TOCTTOU (time of check to time of use) race, since another
client can come along and delete the file in between the file.exists() and new
FileReader(). So since you'll need to handle the FileNotFoundException, I
think you can then drop the file.exists() check.
> Quorum-based protocol for reading and writing edit logs
> -------------------------------------------------------
>
> Key: HDFS-3077
> URL: https://issues.apache.org/jira/browse/HDFS-3077
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: ha, name-node
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Attachments: hdfs-3077-partial.txt, hdfs-3077.txt,
> qjournal-design.pdf, qjournal-design.pdf
>
>
> Currently, one of the weak points of the HA design is that it relies on
> shared storage such as an NFS filer for the shared edit log. One alternative
> that has been proposed is to depend on BookKeeper, a ZooKeeper subproject
> which provides a highly available replicated edit log on commodity hardware.
> This JIRA is to implement another alternative, based on a quorum commit
> protocol, integrated more tightly in HDFS and with the requirements driven
> only by HDFS's needs rather than more generic use cases. More details to
> follow.
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