[
https://issues.apache.org/jira/browse/CASSANDRA-13530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16166519#comment-16166519
]
Ariel Weisberg commented on CASSANDRA-13530:
--------------------------------------------
Why are you still testing with commitlog_sync_batch_window_in_ms set to 2? It
shouldn't be set to a low number. It shouldn't be there at all, but it is and
the only way to disable it is to set to something high enough that it doesn't
get in the way and cause extra syncs with smaller than desired batches.
bq. I drew a diagram to help you understand.
Thanks I get the difference between batch and group I just don't understand the
result.
What I don't understand is why the batch size doesn't increase as operations
queue up waiting to get into the next batch. If an operation can't get into the
current batch it should get into the next batch and the size of that batch
should naturally increase to whatever is necessary and then that should repeat.
What is going on there that prevents batches from being the proper size filled
with backed up operations? Is it doing a bunch of syncs with just one operation
and that is what makes the performance worse? Can we fix that instead by
tracking arrival rate and adapting? Is it possible for us to get good
performance at both low and high concurrency?
I asked to see this not as an average but as a log so I could see the flow of
each individual batch along with timing information so we could answer these
questions.
> 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: groupAndBatch.png, 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|
--
This message was sent by Atlassian JIRA
(v6.4.14#64029)
---------------------------------------------------------------------
To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org
For additional commands, e-mail: commits-h...@cassandra.apache.org
