Yuji Ito created CASSANDRA-13530:
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Summary: GroupCommitLogService
Key: CASSANDRA-13530
URL: https://issues.apache.org/jira/browse/CASSANDRA-13530
Project: Cassandra
Issue Type: Improvement
Reporter: Yuji Ito
Fix For: 2.2.x, 3.0.x, 3.11.x
Attachments: groupCommit22.patch, groupCommit30.patch,
groupCommit3x.patch, 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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