Row cache has to store the entire row. It is a very bad option for wide rows.
On Sunday, December 2, 2012, Mike <mthero...@yahoo.com> wrote: > Hello, > > We recently hit an issue within our Cassandra based application. We > have a relatively new Column Family with some very wide rows (10's of > thousands of columns, or more in some cases). During a periodic > activity, we the range of columns to retrieve various pieces of > information, a segment at a time. > > We do these same queries frequently at various stages of the process, > and I thought the application could see a performance benefit from row > caching. We have a small row cache (100MB per node) already enabled, > and I enabled row caching on the new column family. > > The results were very negative. When performing range queries with a > limit of 200 results, for a small minority of the rows in the new column > family, performance plummeted. CPU utilization on the Cassandra node > went through the roof, and it started chewing up memory. Some queries > to this column family hung completely. > > According to the logs, we started getting frequent GCInspector > messages. Cassandra started flushing the largest mem_tables due to > hitting the "flush_largest_memtables_at" of 75%, and scaling back the > key/row caches. However, to Cassandra's credit, it did not die with an > OutOfMemory error. Its measures to emergency measures to conserve > memory worked, and the cluster stayed up and running. No real errors > showed in the logs, except for Messages getting drop, which I believe > was caused by what was going on with CPU and memory. > > Disabling row caching on this new column family has resolved the issue > for now, but, is there something fundamental about row caching that I am > missing? > > We are running Cassandra 1.1.2 with a 6 node cluster, with a replication > factor of 3. > > Thanks, > -Mike > >
