EBS vs local SSD in terms of latency you are using ms as your unit of measurement. If your query runs for 10s you will not notice anything. What is a few less ms for the life of a 10 second query.
To reiterate what Rob said. The query is probably slow because of your use case / data model, not the underlying disk. On 17 September 2014 14:21, Tony Anecito <adanec...@yahoo.com> wrote: > If you cached your tables or the database you may not see any difference > at all. > > Regards, > -Tony > > > On Tuesday, September 16, 2014 6:36 PM, Mohammed Guller < > moham...@glassbeam.com> wrote: > > > Hi - > > We are running Cassandra 2.0.5 on AWS on m3.large instances. These > instances were using EBS for storage (I know it is not recommended). We > replaced the EBS storage with SSDs. However, we didn't see any change in > read latency. A query that took 10 seconds when data was stored on EBS > still takes 10 seconds even after we moved the data directory to SSD. It is > a large query returning 200,000 CQL rows from a single partition. We are > reading 3 columns from each row and the combined data in these three > columns for each row is around 100 bytes. In other words, the raw data > returned by the query is approximately 20MB. > > I was expecting at least 5-10 times reduction in read latency going from > EBS to SSD, so I am puzzled why we are not seeing any change in performance. > > Does anyone have insight as to why we don't see any performance impact on > the reads going from EBS to SSD? > > Thanks, > Mohammed > > > -- Ben Bromhead Instaclustr | www.instaclustr.com | @instaclustr <http://twitter.com/instaclustr> | +61 415 936 359
