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From "Ariel Weisberg (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13530) GroupCommitLogService
Date Mon, 27 Nov 2017 16:03:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16266982#comment-16266982
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Ariel Weisberg commented on CASSANDRA-13530:
--------------------------------------------

Can we just avoid introducing a longish running test by modifying the test to run faster?
If we increase the concurrency of requests submitted to batch and group commit log we can
get the throughput up so the test completes closer to the speed of the async commit log.

I would prefer to make the test faster vs increasing the timeout.

> 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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