title: cassandra Read performance with Collection
body: <p>I have the following columnfamily defined in cassandra</p>
  
  <pre><code>CREATE TABLE metric (
  period int,
  rollup int,
  tenant text,
  path text,
  time bigint,
  data list&amp;lt;double&gt;,
  PRIMARY KEY ((tenant, period, rollup, path), time)
  ) 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=0.100000 AND
  replicate_on_write='true' AND
  populate_io_cache_on_flush='false' AND
  default_time_to_live=0 AND
  speculative_retry='NONE' AND
  memtable_flush_period_in_ms=0 AND
  compaction={'class': 'SizeTieredCompactionStrategy'} AND
  compression={'sstable_compression': 'LZ4Compressor'};
  </code></pre>
  
  <p>Does the size of data list affect the read performance in cassandra ? If yes how can we measure it..?</p>
  
  <p>The issue is that the time taken to query Data-Set1 from cassandra to get 8640 rows (where # of elements in the data list for each row is 90) for a given path/period/rollup combination is more than the time required to query Data-Set 2 which is 8640 rows of data (where # of elements in the data list for each row is 10). </p>
  
  <p>Also if I run a performance test with 10 users accessing Data-Set1 simultaneously, then I start seeing cassandra timeouts in the backend, and it spends a lot of time in Garbage collection, but the same does not happen when I do the same by querying Data-Set2.</p>
  
  <p>So I am concluding that the number of elements in the data list is affecting performance. </p>
  
  <p>Are you seeing similar performance issues in your cassandra stack....?</p>