Its not particularly important, imo. Also check out Trie Memtables, I found they significantly reduce GC pause time. I also recommend Java 17 and Shenandoah.
On Tue, Sep 16, 2025 at 3:37 AM Isaeed Mohanna <isa...@xsense.co> wrote: > Thank you so much Jon for your input the link you provided are very helpful > I am considering also to migrate to the BTI format would you recommending > doing that before or after switching to UCS or its not important? > ------------------------------ > *From:* Jon Haddad <j...@rustyrazorblade.com> > *Sent:* Thursday, September 11, 2025 6:34 PM > *To:* user@cassandra.apache.org <user@cassandra.apache.org> > *Subject:* Re: TWCS migration to UCS > > Hi Isaeed, > > 1. I can recommend UCS as a replacement for every compaction strategy, > including TWCS. I wrote a bit about it here [1], and we have a Time series > section in the docs [2] > > 2. Your read performance will depend entirely on the number of SSTables > per read. You've got a ton there - p99 is 35. Both have a lot of tuning > options. Using scaling_parameters T4 will result in fewer SSTables than > T4, T8, but will have higher write amplification as you will compact more. > For these types of questions, I lean on easy-cass-lab [3] and > cassandra-easy-stress [4], which was donated to the project a few months > ago. > > 3. UCS naturally groups SSTables by time. Newer SSTables will have lower > density than older ones, so they get compacted together. The behavior of > TWCS windowing, while useful in a lot of ways, makes it impossible for > tables with TWCS to make good use zero copy streaming. You're looking a > more than a 10x difference in streaming performance when compared to the > slow streaming path. I was able to take a cluster from 3TB / node without > the ability to expand (due to streaming failures) to 12TB / node, with UCS > providing quite a bit of the heavy lifting. I wrote a bit about the > impact of streaming on node density and how it impacts cost [5]. > > 4. The docs have some good settings to try. Scaling params: T4, T8 is a > good starting point, and I'd look at 'base_shard_count': '8'. > > Jon > > [1] > https://rustyrazorblade.com/post/2025/07-compaction-strategies-and-performance/ > [2] > https://cassandra.apache.org/doc/5.0/cassandra/managing/operating/compaction/ucs.html > [3] https://github.com/rustyrazorblade/easy-cass-lab > [4] https://github.com/apache/cassandra-easy-stress > [5] https://rustyrazorblade.com/post/2025/03-streaming/ > > > > On Thu, Sep 11, 2025 at 2:28 AM Isaeed Mohanna <isa...@xsense.co> wrote: > > Hi > We have a table that stores metrics but does not have TTL, it is > partitioned by metrics_source, metric_type and clustered by a timestamp. > we are currently using the following TWCS compaction with the settings > below. > {'class': > 'org.apache.cassandra.db.compaction.TimeWindowCompactionStrategy', > 'compaction_window_size': '7', 'compaction_window_unit': 'DAYS', > 'max_threshold': '32', 'min_threshold': '4'} > > Some relevant info from tablestats and table historgram, currently the > performance is sufficint for our usecase. > SSTable count: 529 > Max SSTable size: 15.577GiB > Local read/write ratio: 0.75296SSTables Time Window: 7 DAYS, max duration: > 3707 days 4 hours 58 minutes 47 seconds > Local read count: 3823721 > Local read latency: 2.129 ms > Local write count: 5078241 > Local write latency: 0.011 ms > > Percentile Read Latency Write Latency SSTables > Partition Size Cell Count > 50% 1597.00 10.00 > 12.00 17084 1331 > 75% 1916.00 12.00 > 20.00 29521 2299 > 95% 3973.00 29.00 > 29.00 73457 5722 > 98% 9887.00 35.00 > 29.00 126934 9887 > 99% 14237.00 50.00 > 35.00 182785 11864 > Min 373.00 2.00 > 0.00 36 0 > Max 29521.00 446.00 > 50.00 8409007 654949 > > We have recently upgraded to cassandra 5.0.5 and I have been reading about > UCS, since our data does not have TTL we are accumulating sstables with > time. > > 1. Would you recommend migrating to UCS is it production ready and > safe to use? > 2. My scenario has mixed worload, a constant wrote and occasiouanl > bursts of read. Would UCS result in comparable performance or better to > TWCS? > 3. Because my data has no TLL, Is there an option in UCS to use a > time based compaction in the lower tiers like TWCS and a SizeBased in > higher tier to have the best of both worlds? > 4. Which UCS settings do you think would be a good starting point to > experiemnt. > > > > *Best regards, Isaeed Mohanna* > > > >
