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https://issues.apache.org/jira/browse/HADOOP-9198?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jeff Lord resolved HADOOP-9198.
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Resolution: Fixed
This is a flume issue and will be moved to that jira accordingly.
> Update Flume Wiki and User Guide to provide clearer explanation of BatchSize,
> ChannelCapacity and ChannelTransactionCapacity properties.
> ----------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-9198
> URL: https://issues.apache.org/jira/browse/HADOOP-9198
> Project: Hadoop Common
> Issue Type: Improvement
> Components: documentation
> Reporter: Jeff Lord
>
> It would be good if we refined our wiki and user guide to help explain the
> following in a more clear fashion:
> 1) Batch Size
> 1.a) When configured by client code using the flume-core-sdk , to send
> events to flume avro source.
> The flume client sdk has an appendBatch method. This will take a list of
> events and send them to the source as a batch. This is the size of the number
> of events to be passed to the source at one time.
> 1.b) When set as a parameter on HDFS sink (or other sinks which support
> BatchSize parameter)
> This is the number of events written to file before it is flushed to HDFS
> 2)
> 2.a) Channel Capacity
> This is the maximum capacity number of events of the channel.
> 2.b) Channel Transaction Capacity.
> This is the max number of events stored in the channel per transaction.
> How will setting these parameters to different values, affect throughput,
> latency in event flow?
> In general you will see better throughput by using memory channel as opposed
> to using file channel at the loss of durability.
> The channel capacity is going to need to be sized such that it is large
> enough to hold as many events as will be added to it by upstream agents.
> Ideal flow would see the sink draining events from the channel faster than it
> is having events added by its source.
> The channel transaction capacity will need to be smaller than the channel
> capacity.
> e.g. If your Channel capacity is set to 10000 than Channel Transaction
> Capacity should be set to something like 100.
> Specifically if we have clients with varying frequency of event generation,
> i.e. some clients generating thousands of events/sec, while
> others at a much slower rate, what effect will different values of these
> params have on these clients ?
> Transaction Capacity is going to be what throttles or limits how many events
> the source can put into the channel. This going to vary depending on how many
> tiers of agents/collectors you have setup.
> In general though this should probably be equal to whatever you have the
> batch size set to in your client.
> With regards to the hdfs batch size, the larger your batch size the better
> performance will be. However, keep in mind that if a transaction fails the
> entire transaction will be replayed which could have the implication of
> duplicate events downstream.
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