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https://issues.apache.org/jira/browse/FLINK-9113?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Timo Walther updated FLINK-9113:
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Description:
For local filesystems, it is not guaranteed that the data is flushed to disk
during checkpointing. This leads to data loss in cases of TaskManager failures
when writing to a local filesystem {{org.apache.hadoop.fs.LocalFileSystem}}.
The {{flush()}} method returns a written length but the data is not written
into the file (thus the valid length might be greater than the actual file
size). {{hsync}} and {{hflush}} have no effect either.
It seems that this behavior won't be fixed in the near future:
https://issues.apache.org/jira/browse/HADOOP-7844
One solution would be to call {{close()}} on a checkpoint for local
filesystems, even though this would lead to performance decrease. If we don't
fix this issue, we should at least add proper documentation for it.
was:This issue is closely related to FLINK-7737. By default the bucketing
sink uses HDFS's {{org.apache.hadoop.fs.FSDataOutputStream#hflush}} for
performance reasons. However, this leads to data loss in case of TaskManager
failures when writing to a local filesystem
{{org.apache.hadoop.fs.LocalFileSystem}}. We should use {{hsync}} by default in
local filesystem cases and make it possible to disable this behavior if needed.
> Data loss in BucketingSink when writing to local filesystem
> -----------------------------------------------------------
>
> Key: FLINK-9113
> URL: https://issues.apache.org/jira/browse/FLINK-9113
> Project: Flink
> Issue Type: Bug
> Components: Streaming Connectors
> Reporter: Timo Walther
> Assignee: Timo Walther
> Priority: Major
>
> For local filesystems, it is not guaranteed that the data is flushed to disk
> during checkpointing. This leads to data loss in cases of TaskManager
> failures when writing to a local filesystem
> {{org.apache.hadoop.fs.LocalFileSystem}}. The {{flush()}} method returns a
> written length but the data is not written into the file (thus the valid
> length might be greater than the actual file size). {{hsync}} and {{hflush}}
> have no effect either.
> It seems that this behavior won't be fixed in the near future:
> https://issues.apache.org/jira/browse/HADOOP-7844
> One solution would be to call {{close()}} on a checkpoint for local
> filesystems, even though this would lead to performance decrease. If we don't
> fix this issue, we should at least add proper documentation for it.
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