High Bloom Filter FP Ratio

[Chris Hart]

Hi,

I have create the following table with bloom_filter_fp_chance=0.01:

CREATE TABLE logged_event (
  time_key bigint,
  partition_key_randomizer int,
  resource_uuid timeuuid,
  event_json text,
  event_type text,
  field_error_list map<text, text>,
  javascript_timestamp timestamp,
  javascript_uuid uuid,
  page_impression_guid uuid,
  page_request_guid uuid,
  server_received_timestamp timestamp,
  session_id bigint,
  PRIMARY KEY ((time_key, partition_key_randomizer), resource_uuid)
) WITH
  bloom_filter_fp_chance=0.010000 AND
  caching='KEYS_ONLY' AND
  comment='' AND
  dclocal_read_repair_chance=0.000000 AND
  gc_grace_seconds=864000 AND
  index_interval=128 AND
  read_repair_chance=0.000000 AND
  replicate_on_write='true' AND
  populate_io_cache_on_flush='false' AND
  default_time_to_live=0 AND
  speculative_retry='99.0PERCENTILE' AND
  memtable_flush_period_in_ms=0 AND
  compaction={'class': 'SizeTieredCompactionStrategy'} AND
  compression={'sstable_compression': 'LZ4Compressor'};


When I run cfstats, I see a much higher false positive ratio:

                Table: logged_event
                SSTable count: 15
                Space used (live), bytes: 104128214227
                Space used (total), bytes: 104129482871
                SSTable Compression Ratio: 0.3295840184239226
                Number of keys (estimate): 199293952
                Memtable cell count: 56364
                Memtable data size, bytes: 20903960
                Memtable switch count: 148
                Local read count: 1396402
                Local read latency: 0.362 ms
                Local write count: 2345306
                Local write latency: 0.062 ms
                Pending tasks: 0
                Bloom filter false positives: 147705
                Bloom filter false ratio: 0.49020
                Bloom filter space used, bytes: 249129040
                Compacted partition minimum bytes: 447
                Compacted partition maximum bytes: 315852
                Compacted partition mean bytes: 1636
                Average live cells per slice (last five minutes): 0.0
                Average tombstones per slice (last five minutes): 0.0

Any idea what could be causing this?  This is timeseries data.  Every time we 
read from this table, we read a single row key with 1000 
partition_key_randomizer values.  I'm running cassandra 2.0.11.  I tried 
running an upgradesstables to rewrite them, which didn't change this behavior 
at all.  I'm using size tiered compaction and I haven't done any major 
compactions.

Thanks,
Chris