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Hanson edited comment on CASSANDRA-7549 at 7/16/14 8:37 AM: ------------------------------------------------------------ When the Query needs to access an SSTable, the OS will cache this SSTable. But the Read block size is too small (~40KB observed by “iostat”), so it spends a long time to cache it into memory (my machine has plenty of memory). During the caching period, the Query is very slow (only hundreds TPS); after the caching done, the Query is very fast (several thousands TPS). You mentioned “8Kb read ahead”, is it handled by Cassandra or OS disk driver parameter? I have tried: cat /sys/block/sdb/queue/read_ahead_kb 128 echo 1024 > /sys/block/sdb/queue/read_ahead_kb But no impact to the Read disk I/O per "iostat". was (Author: he902): When the Query needs to access an SSTable, the OS will cache this SSTable. But the Read block size is too small (~40KB observed by “iostat”), so it spends a long time to cache it into memory (my machine has plenty of memory). During the caching period, the Query is very slow (only hundreds TPS); after the caching done, the Query is very fast (thousand TPS). You mentioned “8Kb read ahead”, is it handled by Cassandra or OS disk driver parameter? I have tried: cat /sys/block/sdb/queue/read_ahead_kb 128 echo 1024 > /sys/block/sdb/queue/read_ahead_kb But no impact to the Read disk I/O > Heavy Disk Read I/O > ------------------- > > Key: CASSANDRA-7549 > URL: https://issues.apache.org/jira/browse/CASSANDRA-7549 > Project: Cassandra > Issue Type: Improvement > Environment: Cassandra 2.0.6 > Reporter: Hanson > > We observed heavy disk Read I/O, sometimes almost ~100% disk I/O %util. The > block size for Disk Read seems too small per “iostat”: > - DB Query: ~40KB per read > - SSTables Compaction : ~120KB per read > Could it use larger block size for Disk Read? (from Cassandra or OS disk > driver tuning) -- This message was sent by Atlassian JIRA (v6.2#6252)