+1 to putting it in 5.0
On Tue, Feb 11, 2025 at 2:10 AM Mick Semb Wever <m...@apache.org> wrote: > Any objections to making the following changes also to 5.0 ? > > CASSANDRA-20296 proposes the following changes: > > 1. G1 to by default use `-XX:G1NewSizePercent=50` to floor the young > generation's size to 50% of the heap. (We know in production this can > often be raised to 66% for optimal performance.) > > 2. When using G1, default set `-XX:ParallelGCThreads` and > `-XX:ConcGCThreads` to the number of system cpu cores. (Existing > settings are honoured.) > > 3. The auto-generated heap size is now half the server's physical RAM, > capped at 16G for CMS and 31G for G1. This simplifies, and makes more > appropriate, the previous algorithm. Like before this is only used if > MAX_HEAP_SIZE or -Xmx hasn't been set. > > 4. Increase MaxTenuringThreshold from 1 to 2. Plenty of evidence now > showing it has no negatives (over values of zero or one), but can > sometimes have significant benefits in keeping objects in the young > generation. While values above 2 don't have any noticeable benefit. > > 5. Default set CASSANDRA_HEAPDUMP_DIR to $CASSANDRA_LOG_DIR, to avoid > hprof filling up unexpected disk volumes. Assumption here is that the > logs directory is large enough to handle these dumps, and/or operators > are monitoring these directories more than other randon/unknown > directories. Existing values of CASSANDRA_HEAPDUMP_DIR are honoured. > > > As can be seen, these changes are only going to impact those users > that haven't set any of these flags. And a number of the defaults are > wildly bad. The only question I have is how this might impact the dev > experience on local machines where the ram is already used up. (It > would be a fail-fast and the dev would have to set a lower > MAX_HEAP_SIZE, which I think is trivial compared to the benefits > here.) >
