Regarding the buffer size, it is configurable. My personal take is that we’ve tested this on a variety of hardware (from laptops to large instance sizes) already, as well as a few different disk configs (it’s also been run internally, in test, at a few places) and that it has been reviewed by four committers and another contributor. Always love to see more numbers. if folks want to take it for a spin on Alibaba cloud, azure, etc and determine the best buffer size that’s awesome. We could document which is suggested for the community. I don’t think it’s necessary to block on that however.
Also I am of course +1 to including this in 5.0. Jordan On Wed, Feb 12, 2025 at 19:50 guo Maxwell <cclive1...@gmail.com> wrote: > What I understand is that there will be some differences in block storage > among various cloud platforms. More intuitively, the default read-ahead > size will be the same. For example, AWS ebs seems to be 256K, and Alibaba > Cloud seems to be 512K（If I remember correctly). > > Just like 19488, give the test method, see who can assist in the test , > and provide the results. > > Jon Haddad <j...@rustyrazorblade.com> 于2025年2月13日周四 08:30写道： > >> Can you elaborate why? This would be several hundred hours of work and >> would cost me thousands of $$ to perform. >> >> Filesystems and block devices are well understood. Could you give me an >> example of what you think might be different here? This is already one of >> the most well tested and documented performance patches ever contributed to >> the project. >> >> On Wed, Feb 12, 2025 at 4:26 PM guo Maxwell <cclive1...@gmail.com> wrote: >> >>> I think it should be tested on most cloud platforms（at least >>> aws、azure、gcp） before merged into 5.0 . Just like CASSANDRA-19488. >>> >>> Paulo Motta <pa...@apache.org>于2025年2月13日 周四上午6:10写道： >>> >>>> I'm looking forward to these improvements, compaction needs tlc. :-) >>>> A couple of questions: >>>> >>>> Has this been tested only on EBS, or also EC2/bare-metal/Azure/etc? My >>>> only concern is if this is an optimization for EBS that can be a >>>> deoptimization for other environments. >>>> >>>> Are there reproducible scripts that anyone can run to verify the >>>> improvements in their own environments ? This could help alleviate any >>>> concerns and gain confidence to introduce a perf. improvement in a >>>> patch release. >>>> >>>> I have not read the ticket in detail, so apologies if this was already >>>> discussed there or elsewhere. >>>> >>>> On Wed, Feb 12, 2025 at 3:01 PM Jon Haddad <j...@rustyrazorblade.com> >>>> wrote: >>>> > >>>> > Hey folks, >>>> > >>>> > Over the last 9 months Jordan and I have worked on CASSANDRA-15452 >>>> [1]. The TL;DR is that we're internalizing a read ahead buffer to allow us >>>> to do fewer requests to disk during compaction and range reads. This >>>> results in far fewer system calls (roughly 16x reduction) and on systems >>>> with higher read latency, a significant improvement in compaction >>>> throughput. We've tested several different EBS configurations and found it >>>> delivers up to a 10x improvement when read ahead is optimized to minimize >>>> read latency. I worked with AWS and the EBS team directly on this and the >>>> Best Practices for C* on EBS [2] I wrote for them. I've performance tested >>>> this patch extensively with hundreds of billions of operations across >>>> several clusters and thousands of compactions. It has less of an impact on >>>> local NVMe, since the p99 latency is already 10-30x less than what you see >>>> on EBS (100micros vs 1-3ms), and you can do hundreds of thousands of IOPS >>>> vs a max of 16K. >>>> > >>>> > Related to this, Branimir wrote CASSANDRA-20092 [3], which >>>> significantly improves compaction by avoiding reading the partition index. >>>> CASSANDRA-20092 has been merged to trunk already [4]. >>>> > >>>> > I think we should merge both of these patches into 5.0, as the perf >>>> improvement should allow teams to increase density of EBS backed C* >>>> clusters by 2-5x, driving cost way down. There's a lot of teams running C* >>>> on EBS now. I'm currently working with one that's bottlenecked on maxed >>>> out EBS GP3 storage. I propose we merge both, because without >>>> CASSANDRA-20092, we won't get the performance improvements in >>>> CASSANDRA-15452 with BTI, only BIG format. I've tested BTI in other >>>> situations and found it to be far more performant than BIG. >>>> > >>>> > If we were looking at a small win, I wouldn't care much, but since >>>> these patches, combined with UCS, allows more teams to run C* on EBS at > >>>> 10TB / node, I think it's worth doing now. >>>> > >>>> > Thanks in advance, >>>> > Jon >>>> > >>>> > [1] https://issues.apache.org/jira/browse/CASSANDRA-15452 >>>> > [2] >>>> https://aws.amazon.com/blogs/database/best-practices-for-running-apache-cassandra-with-amazon-ebs/ >>>> > [3] https://issues.apache.org/jira/browse/CASSANDRA-20092 >>>> > [4] >>>> https://github.com/apache/cassandra/commit/3078aea1cfc70092a185bab8ac5dc8a35627330f >>>> > >>>> >>>
