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https://issues.apache.org/jira/browse/FLUME-896?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13229090#comment-13229090
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[email protected] commented on FLUME-896:
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bq. On 2012-03-14 08:27:28, Juhani Connolly wrote:
bq. > This looks like a great start on a tough task...
bq. >
bq. > I'm unsure about one thing that doesn't seem to be covered by tests:
bq. >
bq. > When parallel threads each have their own transactions, there is no
guarantee that FileChannel.commitSequenceId is called in seqid order. Some
threads will already have committed some or all of their entries, but because
of a lower commitSequenceId entry the entries will still be "revived" in replay.
bq. >
bq. > e.g. thread a and b do some puts/takes and commit
bq. >
bq. > action | seqId | lastSequenceId
bq. > a.put | 1
bq. > b.put | 2
bq. > b.put | 3
bq. > a.put | 4
bq. > b.take | | 3
bq. > a.commit
bq. > b.commit
bq. >
bq. > at this point the sequenceId file would just contain 3
bq. > events would contain 1,2,3,4
bq. > channel a would contain 1,4
bq. > channel b would contain 2
bq. >
bq. > Now the process dies, we bring it back, replay the WAL:
bq. >
bq. > - replaying the sequenceId file(s) would detect 3 as the oldest
commitSequenceId
bq. > - only entry 4 would be > 3 and thus restored to entries
bq. > - entries 1,2 which were never take()d have gone missing.
bq. >
bq. > Does this fall within the purview of best effort delivery(so it is
acceptable to lose these since we are not guaranteeing delivery)?
bq. > Or am I missing something?
bq.
bq. Juhani Connolly wrote:
bq. I was going to write a unit test but there's no mechanism to force a
WAL write. While changing implementation for testing isn't good, I think it may
make sense to roll the wall when doClose is called on FileChannel.
Also, I got the example wrong(because of the order take's are made in)... the
lastSequenceId should be 2, resulting in 3,4, getting recovered but 1 still
missing.
With that being said, have you considered treating take's and put's as separate
entries in the wal, with commit id's assigned to them at commit time. You can
then periodically "compact" the wal by replaying its contents, removing matched
takes/puts(you may want to look at how this is done in HBase)?
- Juhani
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-----------------------------------------------------------
On 2012-03-14 01:41:47, Brock Noland wrote:
bq.
bq. -----------------------------------------------------------
bq. This is an automatically generated e-mail. To reply, visit:
bq. https://reviews.apache.org/r/4325/
bq. -----------------------------------------------------------
bq.
bq. (Updated 2012-03-14 01:41:47)
bq.
bq.
bq. Review request for Flume.
bq.
bq.
bq. Summary
bq. -------
bq.
bq. Attached patch not meant for commit. Just posting here for easy review.
bq.
bq.
bq. This addresses bug FLUME-896.
bq. https://issues.apache.org/jira/browse/FLUME-896
bq.
bq.
bq. Diffs
bq. -----
bq.
bq. flume-ng-channels/flume-file-channel/pom.xml ee2d20f
bq.
flume-ng-channels/flume-file-channel/src/main/java/org/apache/flume/channel/file/FileChannel.java
a279453
bq.
flume-ng-channels/flume-file-channel/src/main/java/org/apache/flume/channel/file/FileChannelEvent.java
PRE-CREATION
bq.
flume-ng-channels/flume-file-channel/src/main/java/org/apache/flume/channel/file/wal/WAL.java
PRE-CREATION
bq.
flume-ng-channels/flume-file-channel/src/main/java/org/apache/flume/channel/file/wal/WALDataFile.java
PRE-CREATION
bq.
flume-ng-channels/flume-file-channel/src/main/java/org/apache/flume/channel/file/wal/WALEntry.java
PRE-CREATION
bq.
flume-ng-channels/flume-file-channel/src/main/java/org/apache/flume/channel/file/wal/WALReplyResult.java
PRE-CREATION
bq.
flume-ng-channels/flume-file-channel/src/test/java/org/apache/flume/channel/file/TestFileChannel.java
ab66998
bq.
flume-ng-channels/flume-file-channel/src/test/java/org/apache/flume/channel/file/wal/TestWAL.java
PRE-CREATION
bq.
bq. Diff: https://reviews.apache.org/r/4325/diff
bq.
bq.
bq. Testing
bq. -------
bq.
bq.
bq. Thanks,
bq.
bq. Brock
bq.
bq.
> Implement file write ahead log channel
> --------------------------------------
>
> Key: FLUME-896
> URL: https://issues.apache.org/jira/browse/FLUME-896
> Project: Flume
> Issue Type: New Feature
> Components: Channel
> Affects Versions: NG alpha 1
> Reporter: E. Sammer
> Assignee: E. Sammer
> Fix For: v1.2.0
>
> Attachments: FLUME-896-1.patch
>
>
> Implement a channel that uses a regular file system and a write ahead log for
> durable event delivery.
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