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From "Ariel Weisberg (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13530) GroupCommitLogService
Date Fri, 01 Dec 2017 18:06:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16274711#comment-16274711
] 

Ariel Weisberg commented on CASSANDRA-13530:
--------------------------------------------

The comment for https://github.com/apache/cassandra/compare/trunk...jasobrown:13530?expand=1#diff-bdaab1104a93e723ce0b609a6477c9c4R365
still doesn't make sense. I would go so far as to suggest that we remove commitlog_sync_batch_window_in_ms
from the YAML so people can't abuse it. Move a very basic documentation as to why it's not
useful into Config.java for anyone who finds it and thinks about using it.

I was kind of hoping we could speed up batch and group so they run faster by upping the thread
count. Keeping overall test runtime down is a good thing in and of itself.

+1 otherwise. If you don't want to mess with thread counts that's fine, but we should do something
about the docs for commitlog_sync_batch_window_in_ms. It's to tempting for people to set it
low given the 100% wrong documentation.

> GroupCommitLogService
> ---------------------
>
>                 Key: CASSANDRA-13530
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13530
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Yuji Ito
>            Assignee: Yuji Ito
>             Fix For: 2.2.x, 3.0.x, 3.11.x
>
>         Attachments: GuavaRequestThread.java, MicroRequestThread.java, groupAndBatch.png,
groupCommit22.patch, groupCommit30.patch, groupCommit3x.patch, groupCommitLog_noSerial_result.xlsx,
groupCommitLog_result.xlsx
>
>
> I propose a new CommitLogService, GroupCommitLogService, to improve the throughput when
lots of requests are received.
> It improved the throughput by maximum 94%.
> I'd like to discuss about this CommitLogService.
> Currently, we can select either 2 CommitLog services; Periodic and Batch.
> In Periodic, we might lose some commit log which hasn't written to the disk.
> In Batch, we can write commit log to the disk every time. The size of commit log to write
is too small (< 4KB). When high concurrency, these writes are gathered and persisted to
the disk at once. But, when insufficient concurrency, many small writes are issued and the
performance decreases due to the latency of the disk. Even if you use SSD, processes of many
IO commands decrease the performance.
> GroupCommitLogService writes some commitlog to the disk at once.
> The patch adds GroupCommitLogService (It is enabled by setting `commitlog_sync` and `commitlog_sync_group_window_in_ms`
in cassandra.yaml).
> The difference from Batch is just only waiting for the semaphore.
> By waiting for the semaphore, some writes for commit logs are executed at the same time.
> In GroupCommitLogService, the latency becomes worse if the there is no concurrency.
> I measured the performance with my microbench (MicroRequestThread.java) by increasing
the number of threads.The cluster has 3 nodes (Replication factor: 3). Each nodes is AWS EC2
m4.large instance + 200IOPS io1 volume.
> The result is as below. The GroupCommitLogService with 10ms window improved update with
Paxos by 94% and improved select with Paxos by 76%.
> h6. SELECT / sec
> ||\# of threads||Batch 2ms||Group 10ms||
> |1|192|103|
> |2|163|212|
> |4|264|416|
> |8|454|800|
> |16|744|1311|
> |32|1151|1481|
> |64|1767|1844|
> |128|2949|3011|
> |256|4723|5000|
> h6. UPDATE / sec
> ||\# of threads||Batch 2ms||Group 10ms||
> |1|45|26|
> |2|39|51|
> |4|58|102|
> |8|102|198|
> |16|167|213|
> |32|289|295|
> |64|544|548|
> |128|1046|1058|
> |256|2020|2061|



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