We are using G1 ... On Tue, 11 Feb 2020 at 08:51, Reid Pinchback <rpinchb...@tripadvisor.com> wrote:
> A caveat to the 31GB recommendation for G1GC. If you have tight latency > SLAs instead of throughput SLAs then this doesn’t necessary pan out to be > beneficial. > > > > Yes the GCs are less frequent, but they can hurt more when they do happen. > The win is if your usage pattern is such that the added time helps you > squeak past deciding copying into old gen when a smaller heap/more frequent > GC cycle would have decided it had to do promotions. C* tends to have a > lot of medium-lifetime objects on the heap so it can really come down to > the specifics of what your clients are typically doing. > > > > Also, reallocation of RAM from O/S buffer cache to Java heap will also > change the dynamics of dirty page flushes from your writes, which again > directly surfaces in C* read latency numbers during I/O stalls from the > write spikes in the background. So really bumping up heap is an alteration > that can be a double-whammy for the latency sensitive. Those only caring > about throughput won’t care and it’s probably unconditionally a win to go > to 31GB. > > > > R > > > > *From: *Erick Ramirez <erick.rami...@datastax.com> > *Reply-To: *"user@cassandra.apache.org" <user@cassandra.apache.org> > *Date: *Monday, February 10, 2020 at 3:55 PM > *To: *"user@cassandra.apache.org" <user@cassandra.apache.org> > *Subject: *Re: Overload because of hint pressure + MVs > > > > *Message from External Sender* > > Currently the value of phi_convict_threshold is not set which makes it to > 8 (default) . > Can this also cause hints buildup even when we can see that all nodes are > UP ? > > > > You can bump it up to 12 to reduce the sensitivity but it's likely GC > pauses causing it. Phi convict is the side-effect, not the cause. > > > > Just to add , we are using 24GB heap size. > > > > Are you using CMS? If using G1, I'd recommend bumping it up to 31GB if the > servers have 40+ GB of RAM. Cheers! >
