I think it would make sense to support overriding the default FP in the UCS parameters, so we can treat it as a direct replacement. Desiree FP is directly related to sstable overlaps after all.
Can you think of any other usability gaps like this? > On 9 Dec 2024, at 12:06, Jeff Jirsa <jji...@apache.org> wrote: > > > >> On 2024/12/09 16:26:45 Benedict wrote: >> I think it’s important to remember that UCS broadly speaking subsumes both >> LCS >> and STCS, with various subtle but important refinements. So while it offers a >> broader parameter space it might be best to conceive of it as a suite of >> compaction strategies, two of which are direct replacements to LCS and STCS. >> The existing documentation and guides on how to work with LCS and STCS should >> map straightforwardly to matching UCS parameters. We can probably even >> directly copy much of the existing docs for these modes. >> >> >> >> I wonder if it therefore makes sense to allow named parameter combinations, >> and to provide two defaults - named LCS and STCS? These should map so closely >> to what people understand as LCS and STCS as to make transition very simple. > > > 'Probably', but as you mentioned, there are subtle differences - recall that > LCS changes other default table params like bloomfilter FP ratio, which UCS > doesn't do. > > https://github.com/apache/cassandra/blob/8e355197f07ff2c172f31a740ace4f52e34a0fd9/src/java/org/apache/cassandra/schema/CompactionParams.java#L263-L266 > > UCS' size scaling may hide the offheap memory impact of the different FP > ratio depending on how it's tuned, but doing so also makes sstables (with > wider ranges) less likely to take the zero copy streaming path, etc. > >> Overtime we can perhaps develop more refined parameter combinations and >> suggest users migrate as we understand the parameter space better. >> >> > > > I also think that having short-cuts or abbreviated params would be helpful. I > think I understand compaction pretty well, and I have no idea how I'd setup > scaling_parameters or sstable_growth today.
