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Posted to commits@samza.apache.org by "Chris Riccomini (JIRA)" <ji...@apache.org> on 2014/04/04 02:42:16 UTC
[jira] [Created] (SAMZA-220) SystemConsumers is slow when consuming
from a large number of partitions
Chris Riccomini created SAMZA-220:
-------------------------------------
Summary: SystemConsumers is slow when consuming from a large number of partitions
Key: SAMZA-220
URL: https://issues.apache.org/jira/browse/SAMZA-220
Project: Samza
Issue Type: Bug
Components: container
Affects Versions: 0.6.0
Reporter: Chris Riccomini
We have observed poor throughput when a SamzaContainer is consuming many partitions (100s). The more partitions, the worse the performance gets.
When hooking up VisualVM, two operations take up more than 65% of the CPU in SystemConsumers:
{code}
refresh.maybeCall()
updateMessageChooser
{code}
The problem is that we run each of these operations once before every process() call to a StreamTask. Both of these operations iterate over *all* SystemStreamPartitions that the SystemConsumers is consuming from. If you have hundreds of partitions, it means you do two loops of 100+ items for every message you process. This is true even if the SystemConsumers buffer has a lot of messages (10,000+), and also true even if most systemStreamPartitions have no messages available.
I have two proposed solutions to this problem:
1. Only call refresh.maybeCall() when the total number of buffered messages in the SystemConsumers has dropped below some low watermark.
2. Only have updateMessageChooser call messageChooser.update for systemStreamPartitions that actually *have* a message.
I have implemented this and deployed it on a few jobs, and I am seeing significant performance improvement. From 10k-20k msgs/sec to 50k+.
The trade off, as I see it is really around (1), which will introduce a little latency for topics that are low volume. In such a case, the time from when a message arrives to when it gets refreshed in the buffer, and updated in the chooser increases.
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