Skip site navigation (1) Skip section navigation (2)

Re: Testing Sandforce SSD

From: Greg Smith <greg(at)2ndquadrant(dot)com>
To: Matthew Wakeling <matthew(at)flymine(dot)org>
Cc: Yeb Havinga <yebhavinga(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Testing Sandforce SSD
Date: 2010-07-26 18:34:39
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Matthew Wakeling wrote:
> Yeb also made the point - there are far too many points on that graph 
> to really tell what the average latency is. It'd be instructive to 
> have a few figures, like "only x% of requests took longer than y".

Average latency is the inverse of TPS.  So if the result is, say, 1200 
TPS, that means the average latency is 1 / (1200 transactions/second) = 
0.83 milliseconds/transaction.  The average TPS figure is normally on a 
more useful scale as far as being able to compare them in ways that make 
sense to people.

pgbench-tools derives average, worst-case, and 90th percentile figures 
for latency from the logs.  I have 37MB worth of graphs from a system 
showing how all this typically works for regular hard drives I've been 
given permission to publish; just need to find a place to host it at 
internally and I'll make the whole stack available to the world.  So far 
Yeb's data is showing that a single SSD is competitive with a small 
array on average, but with better worst-case behavior than I'm used to 

Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support

In response to


pgsql-performance by date

Next:From: Greg SmithDate: 2010-07-26 18:40:43
Subject: Re: Testing Sandforce SSD
Previous:From: Greg SpiegelbergDate: 2010-07-26 16:26:45
Subject: Re: Testing Sandforce SSD

Privacy Policy | About PostgreSQL
Copyright © 1996-2017 The PostgreSQL Global Development Group