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From Berin Loritsch <blorit...@apache.org>
Subject [C2] JdbcConnection Suggested Setting
Date Fri, 04 May 2001 16:27:33 GMT
This is to pass on a little knowledge.  The JdbcConnection pool is
set up to use a Hard Resource Limit.  This is by design, because many
DB vendors charge you licensing based on number of simultaneous connections.
Also, the more open connections you have on a machine, the more stress
you place on the networking mechanisms.

There comes a problem, however when you are opperating a machine under
heavy load, and are using many threads to handle connections.  The
Hard Resource Limiting policy then can become a gamble (do I have
enough connections to handle the load?).  In order to minimize the
gamble, here is my formula for finding a good starting point.


1) How many connections does the greediest page require?
     * Keep in mind that the esql logicsheet only requires
       one connection at a time, but the SQLTransformer
       requires two connections at one time.  If both of
       these are used together, then you have 3 simultaneous
       connections open.
     * Do not count actions--they are executed sequentially
       before the page generation process.

2) What is the expected load on my machine?  If you have a relatively
   quiet site, you won't need as many open connections.  If your site
   requires logging in, how many simultaneous users will be active?
     * Calculate 1 thread for every 3pages/second
     * Alternatively count 1 thread for every simultaneous user

Creq = Cpmax * T

where

Creq = total number of required connections
Cpmax = result from step 1 above (Connections/Page Max)
T = number of simultaneous threads

Granted, there is always the possibility of all threads accessing a
database backed page at the same time--so if you force your servlet
engine to only listen to the same number of threads as the JdbcConnectionPool
has connections you will never get the dreaded "Not Enough Resources" Exception.

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