At 02:02 PM 1/8/01 -0800, Sander van Zoest wrote:
>On Mon, 8 Jan 2001, Simon Rosenthal wrote:
>
> > an RDBMS is not much more trouble to purge, if you have a
> > time-of-last-update field. And if you're ever going to access your cache
> > from multiple servers, you definitely don't want to deal with  locking
> > issues for DBM and filesystem based solutions ;=(
>
>RDBMS does bring replication and backup issues. The DBM and FS solutions
>definately have their advantages. It would not be too difficult to write
>a serialized daemon that makes request over the net to a DBM file.
>
>What in you experience makes you pick the overhead of an RDBMS for a simple
>cache in favor of DBM, FS solutions?

We cache user session state  (basically using Apache::Session) in a small 
(maybe 500K records) mysql database , which is accessed by multiple web 
servers. We made an explicit decision NOT to replicate or backup this 
database - it's very dynamic, and the only user visible consequence of a 
loss of the database would be an unexpected login screen - we felt this was 
a tradeoff we could live with.  We have a hot spare mysql instance which 
can be brought into service immediately, if required.

  I couldn't see writing a daemon as you suggested  offering us any 
benefits under those circumstances, given that RDBMS access is built into 
Apache::Session.

I would not be as cavalier as this if we were doing anything more than 
using the RDBMS as a fast cache. With decent hardware (which we have - Sun 
Enterprise servers  with nice fast disks and enough memory) the typical 
record retrieval time  is around 10ms, which  even if slow compared to a 
local FS access is plenty fast enough in the context of the processing we 
do for dynamic pages.

Hope this answers your question.

-Simon



>
>--
>Sander van Zoest                                         [[EMAIL PROTECTED]]
>Covalent Technologies, Inc.                           http://www.covalent.net/
>(415) 536-5218                                 http://www.vanzoest.com/sander/

-----------------------------------------------------
Simon Rosenthal ([EMAIL PROTECTED])          
Web Systems Architect
Northern Light Technology
One Athenaeum Street. Suite 1700, Cambridge, MA  02142
Phone:  (617)621-5296  :       URL:  http://www.northernlight.com
"Northern Light - Just what you've been searching for"

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