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https://issues.apache.org/jira/browse/HDFS-3049?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Colin Patrick McCabe updated HDFS-3049:
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Attachment: HDFS-3049.015.patch
* get rid of the old JournalManager#getInputStream API, which selected a single
EditLogInputStream. This forced us to do a readdir() operations per edit log
segment in FileJournalManager, since we had to iterate over all files in the
directory each time getInputStream was called.
* The new API, selectInputStreams, adds all the streams it can to a collection.
It never throws. One subtle improvement here is that previously we might
sometimes ignore an edit log simply because another edit log threw an exception
when being examined in getInputStream. This is fixed now.
* EditLogFileInputStream: don't open any file descriptors when the edit log is
first materialized. Since we're creating all the edit log structures "up
front" now, this is important.
* EditLogFileInputStream: add class LOG, rather than using FSImage's LOG.
* EditLogInputStream#nextValidOp (default trivial implementation): catch
RuntimeException as well as IOException. nextValidOp is not supposed to throw.
> During the normal loading NN startup process, fall back on a different
> EditLog if we see one that is corrupt
> ------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-3049
> URL: https://issues.apache.org/jira/browse/HDFS-3049
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: name-node
> Affects Versions: 0.23.0
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
> Priority: Minor
> Attachments: HDFS-3049.001.patch, HDFS-3049.002.patch,
> HDFS-3049.003.patch, HDFS-3049.005.against3335.patch,
> HDFS-3049.006.against3335.patch, HDFS-3049.007.against3335.patch,
> HDFS-3049.010.patch, HDFS-3049.011.patch, HDFS-3049.012.patch,
> HDFS-3049.013.patch, HDFS-3049.015.patch
>
>
> During the NameNode startup process, we load an image, and then apply edit
> logs to it until we believe that we have all the latest changes.
> Unfortunately, if there is an I/O error while reading any of these files, in
> most cases, we simply abort the startup process. We should try harder to
> locate a readable edit log and/or image file.
> *There are three main use cases for this feature:*
> 1. If the operating system does not honor fsync (usually due to a
> misconfiguration), a file may end up in an inconsistent state.
> 2. In certain older releases where we did not use fallocate() or similar to
> pre-reserve blocks, a disk full condition may cause a truncated log in one
> edit directory.
> 3. There may be a bug in HDFS which results in some of the data directories
> receiving corrupt data, but not all. This is the least likely use case.
> *Proposed changes to normal NN startup*
> * We should try a different FSImage if we can't load the first one we try.
> * We should examine other FSEditLogs if we can't load the first one(s) we try.
> * We should fail if we can't find EditLogs that would bring us up to what we
> believe is the latest transaction ID.
> Proposed changes to recovery mode NN startup:
> we should list out all the available storage directories and allow the
> operator to select which one he wants to use.
> Something like this:
> {code}
> Multiple storage directories found.
> 1. /foo/bar
> edits__curent__XYZ size:213421345 md5:2345345
> image size:213421345 md5:2345345
> 2. /foo/baz
> edits__curent__XYZ size:213421345 md5:2345345345
> image size:213421345 md5:2345345
> Which one would you like to use? (1/2)
> {code}
> As usual in recovery mode, we want to be flexible about error handling. In
> this case, this means that we should NOT fail if we can't find EditLogs that
> would bring us up to what we believe is the latest transaction ID.
> *Not addressed by this feature*
> This feature will not address the case where an attempt to access the
> NameNode name directory or directories hangs because of an I/O error. This
> may happen, for example, when trying to load an image from a hard-mounted NFS
> directory, when the NFS server has gone away. Just as now, the operator will
> have to notice this problem and take steps to correct it.
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