[jira] [Commented] (FLINK-26586) FileSystem uses unbuffered read I/O

["Anton Kalashnikov (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-26586?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17521637#comment-17521637 ] 

Anton Kalashnikov commented on FLINK-26586:
-------------------------------------------

[~Matthias Schwalbe], big thanks for reporting this problem. Did you have this problem only when you using StateProcessor or for recovery this problem is also relevant?

According to implementation, I don't sure that we should implement bufferization on StreamWrapper I mostly tend to implement it inside `LocalDataInputStream`. Right now we use `FileInputStream` there but perhaps we should use something with bufferization instead. But implementation is discussable.

We also should check do we have a benchmark for a such scenario. If we don't have such a benchmark(I think we don't) we will need to create one.

Do you want to work on this task? (I can assign it to you if so)

> FileSystem uses unbuffered read I/O
> -----------------------------------
>
>                 Key: FLINK-26586
>                 URL: https://issues.apache.org/jira/browse/FLINK-26586
>             Project: Flink
>          Issue Type: Improvement
>          Components: API / State Processor, Connectors / FileSystem, Runtime / Checkpointing
>    Affects Versions: 1.13.0, 1.14.0
>            Reporter: Matthias Schwalbe
>            Priority: Major
>         Attachments: BufferedFSDataInputStreamWrapper.java, BufferedLocalFileSystem.java
>
>
> - I found out that, at least when using LocalFileSystem on a windows system, read I/O to load a savepoint is unbuffered,
>  - See example stack [1]
>  - i.e. in order to load only a long in a serializer, it needs to go into kernel mode 8 times and load the 8 bytes one by one
>  - I coded a BufferedFSDataInputStreamWrapper that allows to opt-in buffered reads on any FileSystem implementation
>  - In our setting savepoint load is now 30 times faster
>  - I’ve once seen a Jira ticket as to improve savepoint load time in general (lost the link unfortunately), maybe this approach can help with it
>  - not sure if HDFS has got the same problem
>  - I can contribute my implementation of a BufferedFSDataInputStreamWrapper which can be integrated in any 
> [1] unbuffered reads stack:
> read:207, FileInputStream (java.io)
> read:68, LocalDataInputStream (org.apache.flink.core.fs.local)
> read:50, FSDataInputStreamWrapper (org.apache.flink.core.fs)
> read:42, ForwardingInputStream (org.apache.flink.runtime.util)
> readInt:390, DataInputStream (java.io)
> deserialize:80, BytePrimitiveArraySerializer (org.apache.flink.api.common.typeutils.base.array)
> next:298, FullSnapshotRestoreOperation$KeyGroupEntriesIterator (org.apache.flink.runtime.state.restore)
> next:273, FullSnapshotRestoreOperation$KeyGroupEntriesIterator (org.apache.flink.runtime.state.restore)
> restoreKVStateData:147, RocksDBFullRestoreOperation (org.apache.flink.contrib.streaming.state.restore)



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