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https://issues.apache.org/jira/browse/HBASE-7643?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Matteo Bertozzi updated HBASE-7643:
-----------------------------------
Status: Patch Available (was: Open)
> HFileArchiver.resolveAndArchive() race condition and snapshot data loss
> -----------------------------------------------------------------------
>
> Key: HBASE-7643
> URL: https://issues.apache.org/jira/browse/HBASE-7643
> Project: HBase
> Issue Type: Bug
> Affects Versions: hbase-6055, 0.96.0
> Reporter: Matteo Bertozzi
> Assignee: Matteo Bertozzi
> Priority: Blocker
> Fix For: 0.96.0, 0.94.5
>
> Attachments: HBASE-7653-p4-v0.patch, HBASE-7653-p4-v1.patch,
> HBASE-7653-p4-v2.patch
>
>
> * The master have an hfile cleaner thread (that is responsible for cleaning
> the /hbase/.archive dir)
> ** /hbase/.archive/table/region/family/hfile
> ** if the family/region/family directory is empty the cleaner removes it
> * The master can archive files (from another thread, e.g. DeleteTableHandler)
> * The region can archive files (from another server/process, e.g. compaction)
> The simplified file archiving code looks like this:
> {code}
> HFileArchiver.resolveAndArchive(...) {
> // ensure that the archive dir exists
> fs.mkdir(archiveDir);
> // move the file to the archiver
> success = fs.rename(originalPath/fileName, archiveDir/fileName)
> // if the rename is failed, delete the file without archiving
> if (!success) fs.delete(originalPath/fileName);
> }
> {code}
> Since there's no synchronization between HFileArchiver.resolveAndArchive()
> and the cleaner run (different process, thread, ...) you can end up in the
> situation where you are moving something in a directory that doesn't exists.
> {code}
> fs.mkdir(archiveDir);
> // HFileCleaner chore starts at this point
> // and the archiveDirectory that we just ensured to be present gets removed.
> // The rename at this point will fail since the parent directory is missing.
> success = fs.rename(originalPath/fileName, archiveDir/fileName)
> {code}
> The bad thing of deleting the file without archiving is that if you've a
> snapshot that relies on the file to be present, or you've a clone table that
> relies on that file is that you're losing data.
> Possible solutions
> * Create a ZooKeeper lock, to notify the master ("Hey I'm archiving
> something, wait a bit")
> * Add a RS -> Master call to let the master removes files and avoid this
> kind of situations
> * Avoid to remove empty directories from the archive if the table exists or
> is not disabled
> * Add a try catch around the fs.rename
> The last one, the easiest one, looks like:
> {code}
> for (int i = 0; i < retries; ++i) {
> // ensure archive directory to be present
> fs.mkdir(archiveDir);
> // ----> possible race <-----
> // try to archive file
> success = fs.rename(originalPath/fileName, archiveDir/fileName);
> if (success) break;
> }
> {code}
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