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https://issues.apache.org/jira/browse/FLINK-10954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17124855#comment-17124855
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Stephan Ewen commented on FLINK-10954:
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I am wondering if we even need to handle multiple directories in the RocksDB
state backend.
If there are multiple directories on different file systems, then we cannot use
them together, because we cannot hardlink across file system boundaries.
If the different directories are on the same file system, then why do we need
different directories at all? Then the effect should be the same if we use one
or more directories, we still have the same storage capacity etc.
Having multiple directories on the same file system is only relevant for the
batch algorithms, because there every directory gets a different async thread
for spilling / pre-fetching.
So, could we simplify this by saying that RocksDB randomly chooses one
directory from the temp.dirs at the beginning, and then all the code assumes a
single local root directory? This sounds like it would lead to the simplest
implementation and not be worse.
What do you think, [~yunta]
> Hardlink from files of previous local stored state might cross devices
> ----------------------------------------------------------------------
>
> Key: FLINK-10954
> URL: https://issues.apache.org/jira/browse/FLINK-10954
> Project: Flink
> Issue Type: Bug
> Components: Runtime / State Backends
> Affects Versions: 1.6.2
> Reporter: Yun Tang
> Assignee: Yun Tang
> Priority: Critical
> Fix For: 1.12.0
>
>
> Currently, local recovery's base directories is initialized from
> '{{io.tmp.dirs}}' if parameter '{{taskmanager.state.local.root-dirs}}' is not
> set. For Yarn environment, the tmp dirs is replaced by its '{{LOCAL_DIRS}}',
> which might consist of directories from different devices, such as
> /dump/1/nm-local-dir, /dump/2/nm-local-dir. The local directory for RocksDB
> is initialized from IOManager's spillingDirectories, which might located in
> different device from local recovery's folder. However, hard-link between
> different devices is not allowed, it will throw exception below:
> {code:java}
> java.nio.file.FileSystemException: target -> souce: Invalid cross-device link
> {code}
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