Hi dev@, Mick asked that I check in w/ the dev list about CASSANDRA-15393. There's some concern regarding the patch and it's suitability for inclusion in 4.0-beta.
CASSANDRA-15393 reduces garbage created by compaction and the read paths by about 25%. It's part of CASSANDRA-15387, which, including this patch, reduces garbage from the read and compaction paths by about 50%. CASSANDRA-15393 does this by supporting byte array backed cell and clustering types, which is acheived by abstracting the backing type (ByteBuffer/byte[]) from the serialization logic. To avoid paying the allocation cost of adding a container object, singleton "accessor" objects are used to operate on the actual data. See here for an example: https://gist.github.com/bdeggleston/52910225b817a8d54353125ca03f521d Mick and Robert Stupp have raised a few concerns, summarized below: 1. The patch is large (208 files / ~3.5k LOC) 2. Concerns about impact on stability 3. Parameterizing cell/clustering value types in this way makes ClassCastExceptions possible. 4. implications of feature freeze The patch is large, but the vast majority of it is adding type parameters to things. The changes here are wide, but not deep. The most complex parts are the collection serializers and other places where we're now having to do offset bookkeeping. These should be carefully reviewed, but they shouldn't be too difficult to verify and I've added some randomized tests to check them against a wide range of schemas. I'll also run some diff tests against clusters internally. Parameterizing cell and clustering values does make ClassCastExceptions possible, but java's type system guards against this for the most part. Regarding the feature freeze, I don't think it applies to performance improvements. Back to the point about stability though: in pracice, compaction gc is a major contributor to cluster instability. In my experience, about 30% of availability issues are gc related. Also, compaction gc tends to be the limiting factor for repair, host replacements, and other topology changes, which limits how quickly you can recover from other issues. So the patch does add some risk, but I think it's a net win for stability. Thoughts? --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@cassandra.apache.org For additional commands, e-mail: dev-h...@cassandra.apache.org
