so.. caching the *queries* ? it seems like a better mechanism would be to cache the actually logical row…, not the physical row.
Query caches just don't work in production, If you re-word your query, or structure it a different way, you get a miss… In my experience.. query caches have a 0% hit rate. On Tue, Jul 1, 2014 at 6:40 PM, Robert Coli <[email protected]> wrote: > On Tue, Jul 1, 2014 at 6:06 PM, Kevin Burton <[email protected]> wrote: > >> you know.. one thing I failed to mention.. .is that this is going into a >> "bucket" and while it's a logical row, the physical row is like 500MB … >> according to compaction logs. >> >> is the ENTIRE physical row going into the cache as one unit? That's >> definitely going to be a problem in this model. 500MB is a big atomic unit. >> > > Yes, the row cache is a row cache. It caches what the storage engine calls > rows, which CQL calls "partitions." [1] Rows have to be assembled from all > of their row fragments in Memtables/SSTables. > > This is a big part of why the "off-heap" row cache's behavior of > invalidation on write is so bad for its overall performance. Updating a > single column in your 500MB row invalidates it and forces you to assemble > the entire 500MB row from disk. > > The only valid use case for the current off-heap row cache seems to be : > very small, very uniform in size, very hot, and very rarely modified. > > https://issues.apache.org/jira/browse/CASSANDRA-5357 > > Is the ticket for replacing the row cache and its unexpected > characteristics with something more like an actual query cache. > > also.. I assume it's having to do a binary search within the physical row >> ? > > > Since the column level bloom filter's removal in 1.2, the only way it can > get to specific columns is via the index. > > =Rob > [1] https://issues.apache.org/jira/browse/CASSANDRA-6632 > -- Founder/CEO Spinn3r.com Location: *San Francisco, CA* blog: http://burtonator.wordpress.com … or check out my Google+ profile <https://plus.google.com/102718274791889610666/posts> <http://spinn3r.com>
