[
https://issues.apache.org/jira/browse/HDDS-2026?focusedWorklogId=301205&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-301205
]
ASF GitHub Bot logged work on HDDS-2026:
----------------------------------------
Author: ASF GitHub Bot
Created on: 26/Aug/19 12:02
Start Date: 26/Aug/19 12:02
Worklog Time Spent: 10m
Work Description: adoroszlai commented on pull request #1349: HDDS-2026.
Overlapping chunk region cannot be read concurrently
URL: https://github.com/apache/hadoop/pull/1349
## What changes were proposed in this pull request?
Only allow a single read/write operation for the same path in `ChunkUtils`,
to avoid `OverlappingFileLockException` due to concurrent reads. This allows
concurrent reads/writes of separate files (as opposed to simply synchronizing
the methods). It might be improved later by storing and reusing the file lock.
Use plain `FileChannel` instead of `AsynchronousFileChannel` for reading,
too, since it was used in synchronous fashion (by calling `.get()`) anyway.
https://issues.apache.org/jira/browse/HDDS-2026
## How was this patch tested?
Added unit test.
Used improved Freon tool from #1341 to perform read of same key from
multiple threads (which revealed the bug in the first place).
```
$ ozone freon ockg -n 1 -p asdf
$ ozone sh key list vol1/bucket1
[ {
"version" : 0,
"size" : 10240,
"keyName" : "asdf/0"
...
} ]
$ ozone freon ocokr -k 'asdf/0'
...
mean rate = 164.39 calls/second
...
mean = 53.75 milliseconds
stddev = 42.11 milliseconds
median = 44.05 milliseconds
...
Total execution time (sec): 6
Failures: 0
Successful executions: 1000
```
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Issue Time Tracking
-------------------
Worklog Id: (was: 301205)
Remaining Estimate: 0h
Time Spent: 10m
> Overlapping chunk region cannot be read concurrently
> ----------------------------------------------------
>
> Key: HDDS-2026
> URL: https://issues.apache.org/jira/browse/HDDS-2026
> Project: Hadoop Distributed Data Store
> Issue Type: Bug
> Components: Ozone Datanode
> Reporter: Doroszlai, Attila
> Assignee: Doroszlai, Attila
> Priority: Critical
> Labels: pull-request-available
> Attachments: HDDS-2026-repro.patch, changes.diff,
> first-cut-proposed.diff
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> Concurrent requests to datanode for the same chunk may result in the
> following exception in datanode:
> {code}
> java.nio.channels.OverlappingFileLockException
> at java.base/sun.nio.ch.FileLockTable.checkList(FileLockTable.java:229)
> at java.base/sun.nio.ch.FileLockTable.add(FileLockTable.java:123)
> at
> java.base/sun.nio.ch.AsynchronousFileChannelImpl.addToFileLockTable(AsynchronousFileChannelImpl.java:178)
> at
> java.base/sun.nio.ch.SimpleAsynchronousFileChannelImpl.implLock(SimpleAsynchronousFileChannelImpl.java:185)
> at
> java.base/sun.nio.ch.AsynchronousFileChannelImpl.lock(AsynchronousFileChannelImpl.java:118)
> at
> org.apache.hadoop.ozone.container.keyvalue.helpers.ChunkUtils.readData(ChunkUtils.java:175)
> at
> org.apache.hadoop.ozone.container.keyvalue.impl.ChunkManagerImpl.readChunk(ChunkManagerImpl.java:213)
> at
> org.apache.hadoop.ozone.container.keyvalue.KeyValueHandler.handleReadChunk(KeyValueHandler.java:574)
> at
> org.apache.hadoop.ozone.container.keyvalue.KeyValueHandler.handle(KeyValueHandler.java:195)
> at
> org.apache.hadoop.ozone.container.common.impl.HddsDispatcher.dispatchRequest(HddsDispatcher.java:271)
> at
> org.apache.hadoop.ozone.container.common.impl.HddsDispatcher.dispatch(HddsDispatcher.java:148)
> at
> org.apache.hadoop.ozone.container.common.transport.server.GrpcXceiverService$1.onNext(GrpcXceiverService.java:73)
> at
> org.apache.hadoop.ozone.container.common.transport.server.GrpcXceiverService$1.onNext(GrpcXceiverService.java:61)
> {code}
> It seems this is covered by retry logic, as key read is eventually successful
> at client side.
> The problem is that:
> bq. File locks are held on behalf of the entire Java virtual machine. They
> are not suitable for controlling access to a file by multiple threads within
> the same virtual machine.
> ([source|https://docs.oracle.com/javase/8/docs/api/java/nio/channels/FileLock.html])
> code ref:
> [{{ChunkUtils.readData}}|https://github.com/apache/hadoop/blob/c92de8209d1c7da9e7ce607abeecb777c4a52c6a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/keyvalue/helpers/ChunkUtils.java#L175]
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