Re: Counters in 0.8 -- conditional?
Thanks. Yes I know it's by no means trivial. I thought in case there was an index on the column on which I want to place condition, the index machinery itself can do the counting (i.e. when the index is updated, the counter is incremented). It doesn't seem too orthogonal to the current implementation, at least from my very limited experience. It's actually not that easy in Cassandra since a main feature is that the writes don't imply a read. But if you want your index to count the number of row where foo=bar, you need when a new column foo=bar is written to know if the column did not exist already in this row, in which cas you should not increment. Similarly, if you write foo=42, you need to check if the previous value was foo=bar and if yes decrement your index. -- Sylvain
Re: Counters in 0.8 -- conditional?
I'm looking at http://wiki.apache.org/cassandra/Counters So, the counter feature -- it doesn't seem to count rows based in criteria, such as index condition. Is that correct? Yes, it's just about supporting counters in and of themselves (which is non-trivial in a distributed system). It is unrelated to counting rows or columns, unless the application happens to use them for that. -- / Peter Schuller
Re: Counters in 0.8 -- conditional?
Thanks. Just wanted to note that counting the number of rows where foo=bar is a fairly ubiquitous task in db applications. In case of big data, trafficking all these data to client just to count something isn't optimal at all. Maxim -- View this message in context: http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Counters-in-0-8-conditional-tp5985214p5986442.html Sent from the cassandra-u...@incubator.apache.org mailing list archive at Nabble.com.
Re: Counters in 0.8 -- conditional?
Thanks. Just wanted to note that counting the number of rows where foo=bar is a fairly ubiquitous task in db applications. In case of big data, trafficking all these data to client just to count something isn't optimal at all. You can ask Cassandra to do the counting, but the cost is still going to involve reading the data on the Cassandra end. Hence, O(n) rather than O(1). (It would obviously be nice if counts could be done O(1), but it's not trivial to implement or obvious how to do it in order for it to be generally useful. Even non-distributed databases like PostgreSQL have issues with that.) -- / Peter Schuller
Re: Counters in 0.8 -- conditional?
Thanks. Yes I know it's by no means trivial. I thought in case there was an index on the column on which I want to place condition, the index machinery itself can do the counting (i.e. when the index is updated, the counter is incremented). It doesn't seem too orthogonal to the current implementation, at least from my very limited experience. Maxim -- View this message in context: http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Counters-in-0-8-conditional-tp5985214p5986871.html Sent from the cassandra-u...@incubator.apache.org mailing list archive at Nabble.com.
