Reid, I've only been working with Cassandra for 2 years, and this echoes my experience as well.
Regarding the cache use, I know every use case is different, but have you experimented and found any performance benefit to increasing its size? Thanks, John Belliveau On Mon, Dec 2, 2019, 11:07 AM Reid Pinchback <rpinchb...@tripadvisor.com> wrote: > Rahul, if my memory of this is correct, that particular logging message is > noisy, the cache is pretty much always used to its limit (and why not, it’s > a cache, no point in using less than you have). > > > > No matter what value you set, you’ll just change the “reached (….)” part > of it. I think what would help you more is to work with the team(s) that > have apps depending upon C* and decide what your performance SLA is with > them. If you are meeting your SLA, you don’t care about noisy messages. > If you aren’t meeting your SLA, then the noisy messages become sources of > ideas to look at. > > > > One thing you’ll find out pretty quickly. There are a lot of knobs you > can turn with C*, too many to allow for easy answers on what you should > do. Figure out what your throughput and latency SLAs are, and you’ll know > when to stop tuning. Otherwise you’ll discover that it’s a rabbit hole you > can dive into and not come out of for weeks. > > > > > > *From: *Hossein Ghiyasi Mehr <ghiyasim...@gmail.com> > *Reply-To: *"user@cassandra.apache.org" <user@cassandra.apache.org> > *Date: *Monday, December 2, 2019 at 10:35 AM > *To: *"user@cassandra.apache.org" <user@cassandra.apache.org> > *Subject: *Re: "Maximum memory usage reached (512.000MiB), cannot > allocate chunk of 1.000MiB" > > > > *Message from External Sender* > > It may be helpful: > https://thelastpickle.com/blog/2018/08/08/compression_performance.html > <https://urldefense.proofpoint.com/v2/url?u=https-3A__thelastpickle.com_blog_2018_08_08_compression-5Fperformance.html&d=DwMFaQ&c=9Hv6XPedRSA-5PSECC38X80c1h60_XWA4z1k_R1pROA&r=OIgB3poYhzp3_A7WgD7iBCnsJaYmspOa2okNpf6uqWc&m=BlMYluADfxjSCocEBuEfptXuOJCAamgGaQreoJcMRJQ&s=rPo3nouxhBU2Yf2HRb2Udl87roS0KkGuPr-l2ferKXA&e=> > > It's complex. Simple explanation, cassandra keeps sstables in memory based > on chunk size and sstable parts. It manage loading new sstables to memory > based on requests on different sstables correctly . You should be worry > about it (sstables loaded in memory) > > > *VafaTech.com - A Total Solution for Data Gathering & Analysis* > > > > > > On Mon, Dec 2, 2019 at 6:18 PM Rahul Reddy <rahulreddy1...@gmail.com> > wrote: > > Thanks Hossein, > > > > How does the chunks are moved out of memory (LRU?) if it want to make room > for new requests to get chunks?if it has mechanism to clear chunks from > cache what causes to cannot allocate chunk? Can you point me to any > documention? > > > > On Sun, Dec 1, 2019, 12:03 PM Hossein Ghiyasi Mehr <ghiyasim...@gmail.com> > wrote: > > Chunks are part of sstables. When there is enough space in memory to cache > them, read performance will increase if application requests it again. > > > > Your real answer is application dependent. For example write heavy > applications are different than read heavy or read-write heavy. Real time > applications are different than time series data environments and ... . > > > > > > > > On Sun, Dec 1, 2019 at 7:09 PM Rahul Reddy <rahulreddy1...@gmail.com> > wrote: > > Hello, > > > > We are seeing memory usage reached 512 mb and cannot allocate 1MB. I see > this because file_cache_size_mb by default set to 512MB. > > > > Datastax document recommends to increase the file_cache_size. > > > > We have 32G over all memory allocated 16G to Cassandra. What is the > recommended value in my case. And also when does this memory gets filled up > frequent does nodeflush helps in avoiding this info messages? > >
