I'm not sure if this is entirely true, but I *think* older version of cassandra used a version of the ConcurrentLinkedHashmap (which backs the row cache) that used the Second Chance algorithm, rather than LRU, which might explain this non-LRU-like behavior. I may be entirely wrong about this though.
-ryan On Thu, Jan 13, 2011 at 11:05 AM, Saket Joshi <sjo...@touchcommerce.com> wrote: > Yes it does change. > > -----Original Message----- > From: Jonathan Ellis [mailto:jbel...@gmail.com] > Sent: Thursday, January 13, 2011 11:01 AM > To: user > Subject: Re: cassandra row cache > > does the cache size change between 2nd and 3rd time? > > On Thu, Jan 13, 2011 at 10:47 AM, Saket Joshi <sjo...@touchcommerce.com> > wrote: >> Hi, >> >> I am running a 15 node cluster ,version 0.6.8, Linux 64bit OS, using > mmap >> I/O, 6GB ram allocated. I have row cache enabled to 80000 keys (mean > row >> size is 2KB). I am observing a strange behaviour.. I query for 1.6 > Million >> rows across the cluster and time taken is around 40 mins , I query the > same >> data again , the time now is 25 mins to fetch data (i am expecting the > cache >> to be warm now) , but i see row cache hit rate around 30% . Now i > request >> the same data 3rd time, time to fetch is under 4 mins and cache hit > ratios >> are 99% ... Does any one have an idea why this may be happening ? >> >> >> >> >> >> Thanks, >> >> Saket > > > > -- > Jonathan Ellis > Project Chair, Apache Cassandra > co-founder of Riptano, the source for professional Cassandra support > http://riptano.com >
