> If one big query doesn't cause problems Every row you read becomes a (roughly) RF number of tasks in the cluster. If you ask for 100 rows in one query it will generate 300 tasks that are processed by the read thread pool which as a default of 32 threads. If you ask for a lot of rows and the number of nodes in low there is a chance the client starve others as they wait for all the tasks to be completed. So i tend to like asking for fewer rows.
Cheers ----------------- Aaron Morton New Zealand @aaronmorton Co-Founder & Principal Consultant Apache Cassandra Consulting http://www.thelastpickle.com On 7/11/2013, at 12:19 pm, Dan Gould <d...@chill.com> wrote: > Thanks Nate, > > I assume 10k is the return limit. I don't think I'll ever get close to 10k > matches to the IN query. That said, you're right: to be safe I'll increase > the limit to match the number of items on the IN. > > I didn't know CQL supported stored procedures, but I'll take a look. I > suppose my question was asking about parsing overhead, however. If one big > query doesn't cause problems--which I assume it wouldn't since there can be > multiple threads parsing and I assume C* is smart about memory when > accumulating results--I'd much rather do that. > > Dan > > On 11/6/13 3:05 PM, Nate McCall wrote: >> Unless you explicitly set a page size (i'm pretty sure the query is >> converted to a paging query automatically under the hood) you will get >> capped at the default of 10k which might get a little weird semantically. >> That said, you should experiment with explicit page sizes and see where it >> gets you (i've not tried this yet with an IN clause - would be real curious >> to hear how it worked). >> >> Another thing to consider is that it's a pretty big statement to parse every >> time. You might want to go the (much) smaller batch route so these can be >> stored procedures? (another thing I havent tried with IN clause - don't see >> why it would not work though). >> >> >> >> >> On Wed, Nov 6, 2013 at 4:08 PM, Dan Gould <d...@chill.com> wrote: >> I was wondering if anyone had a sense of performance/best practices >> around the 'IN' predicate. >> >> I have a list of up to potentially ~30k keys that I want to look up in a >> table (typically queries will have <500, but I worry about the long tail). >> Most >> of them will not exist in the table, but, say, about 10-20% will. >> >> Would it be best to do: >> >> 1) SELECT fields FROM table WHERE id in (uuid1, uuid2, ...... uuid30000); >> >> 2) Split into smaller batches-- >> for group_of_100 in all_30000: >> // ** Issue in parallel or block after each one?? >> SELECT fields FROM table WHERE id in (group_of_100 uuids); >> >> 3) Something else? >> >> My guess is that (1) is fine and that the only worry is too much data >> returned (which won't be a problem in this case), but I wanted to check that >> it's not a C* anti-pattern before. >> >> [Conversely, is a batch insert with up to 30k items ok?] >> >> Thanks, >> Dan >> >> >> >> >> -- >> ----------------- >> Nate McCall >> Austin, TX >> @zznate >> >> Co-Founder & Sr. Technical Consultant >> Apache Cassandra Consulting >> http://www.thelastpickle.com >
