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From "Hiroyuki Yamada (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13530) GroupCommitLogService
Date Wed, 06 Sep 2017 13:24:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16155319#comment-16155319
] 

Hiroyuki Yamada commented on CASSANDRA-13530:
---------------------------------------------

I'm sorry from outside.

What do you mean `That documentation in the YAML looks wrong to me.` ?
In the apache doc, it also states 2ms is the default value.
http://cassandra.apache.org/doc/latest/configuration/cassandra_config_file.html

I'm not really sure what you are trying to say here, 
but the current batch is not working as expected as I described below, and it is not very
useful.
https://issues.apache.org/jira/browse/CASSANDRA-12864

Even if `commitlog_sync_batch_window_in_ms` is set a big number, 
it is the maximum length of time that queries may be batched together for, not the minimum,
so, it is pretty nondeterministic and the behavior is not predictable.
You can't really balance between latency and throughput.

On the other hand, GroupCommitLogService makes more sense and 
actually makes things very different from performance perspective and it seems behaving pretty
predictable.
Also, It only updates few lines of code changes without much complication.

I'm sorry from outside, but this discussion seems unnecessarily long without good directions
even though the proposal looks pretty good.

> 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: groupCommit22.patch, groupCommit30.patch, groupCommit3x.patch, groupCommitLog_noSerial_result.xlsx,
groupCommitLog_result.xlsx, GuavaRequestThread.java, MicroRequestThread.java
>
>
> 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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