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From Tyler Hobbs <>
Subject Re: High Bloom filter false ratio
Date Thu, 18 Feb 2016 16:57:27 GMT
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

There are also a couple of recent improvements to bloom filters:

On Thu, Feb 18, 2016 at 1:35 AM, Anishek Agarwal <> 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 <>

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