How many partition keys exists for the table which shows this problem (or provide nodetool cfstats for that table)?
On Thu, Feb 18, 2016 at 11:38 AM, daemeon reiydelle <daeme...@gmail.com> wrote: > The bloom filter buckets the values in a small number of buckets. I have > been surprised by how many cases I see with large cardinality where a few > values populate a given bloom leaf, resulting in high false positives, and > a surprising impact on latencies! > > Are you seeing 2:1 ranges between mean and worse case latencies (allowing > for gc times)? > > Daemeon Reiydelle > On Feb 18, 2016 8:57 AM, "Tyler Hobbs" <ty...@datastax.com> wrote: > >> You can try slightly lowering the bloom_filter_fp_chance on your table. >> >> Otherwise, it's possible that you're repeatedly querying one or two >> partitions that always trigger a bloom filter false positive. You could >> try manually tracing a few queries on this table (for non-existent >> partitions) to see if the bloom filter rejects them. >> >> Depending on your Cassandra version, your false positive ratio could be >> inaccurate: https://issues.apache.org/jira/browse/CASSANDRA-8525 >> >> There are also a couple of recent improvements to bloom filters: >> * https://issues.apache.org/jira/browse/CASSANDRA-8413 >> * https://issues.apache.org/jira/browse/CASSANDRA-9167 >> >> >> On Thu, Feb 18, 2016 at 1:35 AM, Anishek Agarwal <anis...@gmail.com> >> wrote: >> >>> Hello, >>> >>> We have a table with composite partition key with humungous cardinality, >>> its a combination of (long,long). On the table we have >>> bloom_filter_fp_chance=0.010000. >>> >>> On doing "nodetool cfstats" on the 5 nodes we have in the cluster we are >>> seeing "Bloom filter false ratio:" in the range of 0.7 -0.9. >>> >>> I thought over time the bloom filter would adjust to the key space >>> cardinality, we have been running the cluster for a long time now but have >>> added significant traffic from Jan this year, which would not lead to >>> writes in the db but would lead to high reads to see if are any values. >>> >>> Are there any settings that can be changed to allow better ratio. >>> >>> Thanks >>> Anishek >>> >> >> >> >> -- >> Tyler Hobbs >> DataStax <http://datastax.com/> >> >
