I agree, the page is clearly misleading in its formulation. However, for the sake of being precise, I'll note that it is not untrue strictly speaking. If replicate_on_write is true (the default that you should probably not change unless you consider yourself an expert in the Cassandra counters implementation), the a write will be written to all replica, and that does not depend of the consistency level of the operation. *But*, please note that this is also true for *every* other write in Cassandra. I.e. for non-counters writes, we *always* replicate the write to every replica regardless of the consistency level. The only thing the CL change is how many acks from said replica we wait for before returning a success to the client. And it works the exact same way for counters with replicate_on_write.
Or put another way, by default, counters works exactly as normal writes as far CL is concerned. So no, replicate_on_write does *not* set the CL to ALL regardless of what you set. However, if you set replicate_on_write to false, we will only write the counter to 1 replica. Which means that the only CL that you will be able to use for writes is ONE (we don't allow ANY for counters). -- Sylvain On Fri, May 31, 2013 at 9:20 AM, Peter Schuller <peter.schul...@infidyne.com > wrote: > This is incorrect. IMO that page is misleading. > > replicate on write should normally always be turned on, or the change > will only be recorded on one node. Replicate on write is asynchronous > with respect to the request and doesn't affect consistency level at > all. > > > On Wed, May 29, 2013 at 7:32 PM, Andrew Bialecki > <andrew.biale...@gmail.com> wrote: > > To answer my own question, directly from the docs: > > > http://www.datastax.com/docs/1.0/configuration/storage_configuration#replicate-on-write > . > > It appears the answer to this is: "Yes, CL.QUORUM isn't necessary for > > reads." Essentially, replicate_on_write sets the CL to ALL regardless of > > what you actually set it to (and for good reason). > > > > > > On Wed, May 29, 2013 at 9:47 AM, Andrew Bialecki < > andrew.biale...@gmail.com> > > wrote: > >> > >> Quick question about counter columns. In looking at the > replicate_on_write > >> setting, assuming you go with the default of "true", my understanding > is it > >> writes the increment to all replicas on any increment. > >> > >> If that's the case, doesn't that mean there's no point in using > CL.QUORUM > >> for reads because all replicas have the same values? > >> > >> Similarly, what effect does the read_repair_chance have on counter > columns > >> since they should need to read repair on write. > >> > >> In anticipation a possible answer, that both CL.QUORUM for reads and > >> read_repair_chance only end up mattering for counter deletions, it's > safe to > >> only use CL.ONE and disable the read repair if we're never deleting > >> counters. (And, of course, if we did start deleting counters, we'd need > to > >> revert those client and column family changes.) > > > > > > > > -- > / Peter Schuller (@scode, http://worldmodscode.wordpress.com) >
