[Exim] Performance comparison, LDAP vs. lsearch

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Autor: Christian Balzer
Data:  
Para: exim-users
Asunto: [Exim] Performance comparison, LDAP vs. lsearch
Hello,

I'm trying to get a rough, rule of thumb, ballpark figure of where
the break even point of doing lsearch local file lookups versus ones
to a remote LDAP database might be.

Lets assume that there are no I/O, network or CPU bottlenecks in either
scenario, what I'm trying to compare here is the cost (time wise) in
query setup and execution.
A further assumption would be that for each mail/address a total of 20
lookups will be required. I can hear the shouts of "Twenty? How did the
loon wind up with that high number?" already, but it's a good estimate
for what I have in mind.

With LDAP one is looking at the overhead to establish a TCP connection to
a remote system, but the database queries are of course a lot faster than
lsearch (at least after a certain DB size).
With lsearch the TCP overhead is gone, the files will be completely cached
for all practical purposes and fast, up a point.

Right now one example would be a 140KB file with 7500 addresses in it
(users that have a specific spam filtering activated) which seems faster
or at least as fast as LDAP.

My gut feeling is that lsearch would do fine (on this particular hardware)
up to about 1MB file size and 50000 addresses before LDAP becomes a
decisively better choice.

Any (educated) guesses and insights how realistic this is and where that
break even point might be?

Regards,

Christian Balzer
--
Christian Balzer        Network Engineer        Engineering
chibi@???       Global OnLine Japan/Exodus Communications K.K.
http://www.gol.com/