Hi Garvit, When updating counters, Cassandra does a read then a write, so there is an overhead of using counters. This is all explained here: https://www.datastax.com/dev/blog/whats-new-in-cassandra-2-1-a-better-implementation-of-counters <https://www.datastax.com/dev/blog/whats-new-in-cassandra-2-1-a-better-implementation-of-counters>
There is a design pattern that can be used instead of counters, this will not work if you need instant accuracy, but if you are looking for a count value to be “eventually" correct then it will be a lot less taxing on cassandra. I have outlined this pattern in a blog post, when I wrote it I was advising a team that was performing a lot of count(*) on a table, so it starts from that premise rather than using counters, but the result is the same. This can be found here: http://www.redshots.com/cassandra-counting-without-using-counters/ <http://www.redshots.com/cassandra-counting-without-using-counters/> I hope these links help. Regards Paul Chandler > On 29 May 2019, at 10:18, Attila Wind <attilaw@swf.technology> wrote: > > Hi Garvit, > > I can not answer your main question but when I read your lines one thing was > popping up constantly: "why do you ask this?" > > So what is the background of this question? Do you see anything smelly? > > Actually > a) I always assumed so naturally there are of course lots of in-parallel > activities (writes) against any tables includin counters. So of course there > is a race condition and probably threads yes > > b) Cassandra do not have isolated transactions so of course in a complex flow > (using multiple tables) there is no business data consistency guarantee for > sure > > c) until you are doing just +/- ops it is a mathematical fact that execution > order of writes is not really important. Repeating +1 increase 5 times will > result in higher counter by num 5... > > Please share your background I am interested in it! > > Cheers > Attila > > 2019. máj. 29., Sze 2:34 dátummal Garvit Sharma <garvit...@gmail.com > <mailto:garvit...@gmail.com>> ezt írta: > Hi, > > I am using counter tables in Cassandra and I want to understand how the > concurrent updates to counter table are handled in Cassandra. > > There are more than one threads who are responsible for updating the counter > for a partition key. Multiple threads can also update the counter for the > same key. > > In case when more than one threads updating the counter for the same key, how > Cassandra is handling the race condition? > > UPDATE cycling.popular_count > SET popularity = popularity + 1 > WHERE id = 6ab09bec-e68e-48d9-a5f8-97e6fb4c9b47; > > Are there overheads of using counter tables? > Are there alternatives to counter tables? > > Thanks, > -- > > Garvit Sharma > github.com/garvitlnmiit/ <http://github.com/garvitlnmiit/> > > No Body is a Scholar by birth, its only hard work and strong determination > that makes him master.
