[jira] [Resolved] (CASSANDRA-7549) Heavy Disk Read I/O

["Benedict (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-7549?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Benedict resolved CASSANDRA-7549.
---------------------------------

    Resolution: Invalid

What you're asking for is not generally optimal behaviour, so is not something we would consider defaulting to in Cassandra. For a dataset larger than memory reading more data than you need to answer the query is going to severely hurt performance. What you probably want to do is to set populate_io_cache_on_flush to true, so that the data is left in memory after a flush (by default in 2.0 it is evicted to ensure other live data is not affected, although in 2.1 this is no longer the case)

> 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)



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