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From: larry@xanadu.uucp (Larry Rowe)
Newsgroups: comp.misc,comp.databases
Subject: Re: RDBMS performance - disks, cache, O/S
Message-ID: <3329@zen.berkeley.edu>
Date: Tue, 18-Aug-87 21:41:19 EDT
Article-I.D.: zen.3329
Posted: Tue Aug 18 21:41:19 1987
Date-Received: Thu, 20-Aug-87 06:38:25 EDT
References: <1170@geac.UUCP>
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Reply-To: larry@xanadu.UUCP (Larry Rowe)
Organization: Postgres Research Group, UC Berkeley
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Xref: mnetor comp.misc:1064 comp.databases:423

In article <1170@geac.UUCP> john@geac.UUCP (John Henshaw) writes:
>Every time I try to have a meaningful discussion regarding the relative
>performance of various RDBMSs, the issue of comparing disk/memory performance
>arises. ...

unfortunately, it is much worse than that.  i've noticed that the load factor
and distribution of free pages on a disk system can have a dramatic
impact on the avg i/o time, hence the benchmark time.  

my sense is that the systems are roughly comparable if there isn't a major
difference.  for example, suppose system A does .5 TP1's a second and
system B does 5 TP1's a second.  this is probably a measurable difference
attributable to differences in the implementations (e.g., how good is the
query optimizer, is reading/writing the log optimized, does the system
do group commits, etc.).  however, even with this big a difference it
may be that system A isn't installed properly (i.e., not enough memory
is allocated for buffers, or locks, or ...). 

in general, my advice is...
1. pick a representative benchmark you want to compare the system on.
(choose this carefully, don't let a vendor define this for you since the
vendor will slant the benchmark to what he knows his system will do well.)
2. run the benchmark.
3. show it to both vendors, ask them to help you improve it.

then, throw out the results from the benchmark and ask yourself:
1. which system was easiest to use?
2. which vendor helped you the most?  (remember, the vendor had better
help you before you spend your money, because he's not likely to give
you more help after he's got your money.)
3. which system gave you twice the maximum performance you think you need.

these questions will help you figure out which system/vendor is likely
to help you solve your problem.  lastly, find another user of the system
that has a nearly identical application and workload to your environment
and ask him which system solves his problem.

life's not easy, but you don't have to find the absolutely optimal 
performing system.
	larry