title: cassandra read high iowait
body: <p><a href="https://i.stack.imgur.com/OQQRV.png" rel="nofollow noreferrer">data read per second</a></p>
  
  <p>I have a three node cassandra cluster。when I have multi thread querying from the cluster ,the io load is very high.The cluster holds about 80GB data per node.I use time window compact strategy and  time-window is ten hour.One sstable is about 1GB.Can some body help me with it.Thank you.<a href="https://i.stack.imgur.com/g71E0.png" rel="nofollow noreferrer">one sstable infomation </a><br>
  data is at a speed of 10000 per second .the cluster holds about 10 billion records .
  below is the schema information </p>
  
  <pre><code>CREATE TABLE point_warehouse.point_period (
      point_name text,
      year text,
      time timestamp,
      period int,
      time_end timestamp,
      value text,
      PRIMARY KEY ((point_name, year), time)
  ) WITH CLUSTERING ORDER BY (time DESC)
      AND bloom_filter_fp_chance = 0.01
      AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
      AND comment = ''
      AND compaction = {'class': 'org.apache.cassandra.db.compaction.TimeWindowCompactionStrategy', 'compaction_window_size': '10', 'compaction_window_unit': 'HOURS', 'max_threshold': '32', 'min_threshold': '4'}
      AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
      AND crc_check_chance = 1.0
      AND dclocal_read_repair_chance = 0.1
      AND default_time_to_live = 2592000
      AND gc_grace_seconds = 864000
      AND max_index_interval = 2048
      AND memtable_flush_period_in_ms = 0
      AND min_index_interval = 128
      AND read_repair_chance = 0.0
      AND speculative_retry = '99PERCENTILE';
  </code></pre>
  
  <p>and the query is <code>SELECT * from  POINT_PERIOD where POINT_NAME=? AND YEAR='2017' AND TIME &gt;'2017-05-23 12:53:24</code> order by time asc   LIMIT 1  ALLOW FILTERING'</p>
  
  <p>when execute this query concurrently the io load became extremely high like 200MB/s. thank you .</p>