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https://issues.apache.org/jira/browse/CASSANDRA-13530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16227031#comment-16227031
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Ariel Weisberg commented on CASSANDRA-13530:
--------------------------------------------
So we can't change existing behavior. So adding a new commit log service as you
have done is fine. The only blocker is documentation and a unit test.
For documentation:
* Class level doc for {{GroupCommitLogService}}
* cassandra.yaml documentation for commitlog_sync "group"
* commitlog_sync_group_window_in_ms
For the unit test running with group configured and then replaying it is fine.
We probably already have this kind of test for the existing implementations.
> 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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