Does that mean that Batch is not working as designed? If there are other pending writes, Batch should also group them together. (Did you test with giving Batch the same window size as Group?)
On Sat, May 13, 2017 at 10:08 AM, Yuji Ito <y...@imagine-orb.com> wrote: > Batch outperforms when there is no concurrency. > Because GroupCommit should wait the window time, the throughput and the > latency are worse in a single request. > GroupCommit can gather the commitlog writes which are requested in the > window time. > Actually, the throughput of a single thread was bounded by the window time. > > Yuji > > On Sat, May 13, 2017 at 11:49 PM, Jonathan Ellis <jbel...@gmail.com> > wrote: > >> Can we replace Batch entirely with this, or are there situations where >> Batch would outperform (in latency, for instance)? >> >> On Sat, May 13, 2017 at 7:21 AM, Yuji Ito <y...@imagine-orb.com> wrote: >> >>> Hi dev, >>> >>> 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%. >>> >>> ==== 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 >>> >>> ==== 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 >>> >>> >>> Thanks, >>> Yuji >>> >>> >>> >>> --------------------------------------------------------------------- >>> To unsubscribe, e-mail: dev-unsubscr...@cassandra.apache.org >>> For additional commands, e-mail: dev-h...@cassandra.apache.org >>> >> >> >> >> -- >> Jonathan Ellis >> co-founder, http://www.datastax.com >> @spyced >> > > -- Jonathan Ellis co-founder, http://www.datastax.com @spyced
