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From "Jun Rao (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-631) Implement log compaction
Date Mon, 28 Jan 2013 06:05:12 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-631?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13564072#comment-13564072

Jun Rao commented on KAFKA-631:

Thanks for patch v7. Looks good overall. Some comments:

70. LogCleaner:
70.1 buildOffsetMap(): need to consider grow readBuffer to accomodate for maxMessageSize.
70.2 celanInto(): Can the payload ever be null?
        val retainRecord = lastOffset < 0 || (entry.offset >= lastOffset &&
entry.message.payload != null)
70.3 CleanerThread.run(): Should we catch all Throwables, instead of Exceptions?

71. Log:
71.1 loadSegments(): The following comment is no longer true since it can happen to a segment
with SwapFileSuffix.
        if(!hasIndex) {
          // this can only happen if someone manually deletes the index file
71.2 maybeRoll(): move .format in debug to a separate line.
71.3 truncateFullyAndStartAt(): This one behaves in the same way as truncateTo and is called
directly from ReplicaFetcherThread. So need to increment truncates here too.

72. KafkaConfig: Why do we have log.cleaner.enable? Shouldn't log cleaner be automatically
enabled if logCleanupPolicy is dedup?

> Implement log compaction
> ------------------------
>                 Key: KAFKA-631
>                 URL: https://issues.apache.org/jira/browse/KAFKA-631
>             Project: Kafka
>          Issue Type: New Feature
>          Components: core
>    Affects Versions: 0.8.1
>            Reporter: Jay Kreps
>            Assignee: Jay Kreps
>         Attachments: KAFKA-631-v1.patch, KAFKA-631-v2.patch, KAFKA-631-v3.patch, KAFKA-631-v4.patch,
KAFKA-631-v5.patch, KAFKA-631-v6.patch, KAFKA-631-v7.patch
> Currently Kafka has only one way to bound the space of the log, namely by deleting old
segments. The policy that controls which segments are deleted can be configured based either
on the number of bytes to retain or the age of the messages. This makes sense for event or
log data which has no notion of primary key. However lots of data has a primary key and consists
of updates by primary key. For this data it would be nice to be able to ensure that the log
contained at least the last version of every key.
> As an example, say that the Kafka topic contains a sequence of User Account messages,
each capturing the current state of a given user account. Rather than simply discarding old
segments, since the set of user accounts is finite, it might make more sense to delete individual
records that have been made obsolete by a more recent update for the same key. This would
ensure that the topic contained at least the current state of each record.

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