From: johnl@obelix.informix.com (Jonathan Leffler)
Newsgroups: comp.databases.informix
Subject: Re:  SE vs OL - Lets get to the crux.
Date: 13 Nov 1992 12:43:07 -0500
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Reply-To: johnl@obelix.informix.com (Jonathan Leffler)
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>From: uunet!elsouth!john (John White)
>Subject: SE vs OL - Lets get to the crux.
>Date: Fri, 6 Nov 1992 19:41:29 GMT
>X-Informix-List-Id: <news.2079>

John says:
>   On the other hand, I do think this is the right forum for
>one of the non-application-specific issues that was brought up.
>It has been repeatedly pointed out that OnLine doesn't show its
>performance increase at lower user numbers. I've been promised that
>OnLine is buttloads better when the user count goes up. I don't
>think so.

>   TEST:
>   o Put 50 users on each of two machines
>   o One machine running OnLine
>   o One running Standard Engine
>   o Have all of the users pull up perform screens.
>   o Have the users do nothing (easy).
>   o Run database performance tests on each machine.

>   I think you'll get very similar numbers to when there is a single
>user. I submit that the important factor in the equation is not the
>number of users, it is more likely the number or transactions per
>second, or the number of transactions per user per second.

I wouldn't regard 50 people doing nothing as 50 users -- what people mean
is that when 50 users are using the database more or less actively, the
pooling of the data with OnLine gives performance benefits which are not
available with SE.  So, yes, you are right, it is the number of
transactions going on per user per second which is relevant, but the number
of users involved is also relevant, not least because if one user is held
up waiting for data from disc, other user's can be dealt with, whereas if
there is only one user, the system has to wait in idle mode.

>   Having said that and feeling the incoming corrections in my
>peripheral conscience, I ask four things:

>   1) That we stick to the subject at hand. I don't want to hear about
>      how performance is not the issue, because performance IS the
>      issue.

Agreed.

>   2) If I'm wrong, what is the correct answer? What is that elusive
>      most-important-factor (X), that as X increases, the performance
>      of OnLine does not degrade as rapidly as Standard Engine.

I would suggest that X is the number of concurrent, active users.

>   3) How does a person measure this factor on his active system? How
>      can I say with confidence that at my shop X = 4.63?

Is this the same X?  I'm not clear.

>   4) What is the break point? At what point do the performance gains
>      that OnLine brings make up for its overhead costs? i.e. When X > 2.

It depends on the size of the database, the user population, the required
availability of the database.  And which X are we referring to?

Fundamentally, the answer will vary from installation to installation,
depending on the workload.  Not very satisfactory for anyone as an answer,
but "It depends..." is depressingly often the best answer one can give.  I
spend a lot of my time saying "It depends..." and elaborating what it
depends on.

Yours,
Jonathan Leffler (johnl@obelix.informix.com) #include <disclaimer.h>