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Date: Fri, 17 Feb 2012 20:53:02 -0500
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Subject: how to best implement my own connection pool
From: Sam Carleton <scarleton@miltonstreet.com>
To: modules-dev@httpd.apache.org
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I am working on a short term solution to a bigger issue.  The long term
solution is switch databases, that is next on the list, after I patch the
current DB.

My background:  I am the sole developer of this product that uses lots of
technologies, one of them is Apache Modules.  It has been a long while,
likes a year+ since I have had to do anything really hard core, so I am not
100% up to speed with terms and exact techniques.  My ultimate goal in this
post is to get some definition/direction as to know were to start on this
short term solution.

I am currently using the DB, SQLite.  It is a great and outstanding DB,
except...  It is File Locking database, when one thread/process writes to
it, the whole DB is locked.  This is all fine and dandy, except there is
one query (not an update/insert/delete) that is pretty intensive and runs a
LOT, could be as much as 10~20 times a second.  The great part is... It is
somewhat static, so I would like to create a system to pool the result in
memory and refresh it when it needs to be changed.  Here is the pseudo
code:

Process 1 (not Apache) that creates the static file:

   1. Create a Lock file: query.results.lock
   2. Dump results from query to a text file: query.results
   3. Remove Lock file

Right now a request comes in via Axis2/C module (a web service).  The WS is
what needs access to this new piece.  I have already done a lot of hacking
on the Axis2/C piece so within the WS code, I have access to the core of
the Apache request, server, etc.  So in the WS, I want to make a call into
this "connection pooling" code to do the following:

   1. Check to see if query.results is in memory, if not load it
   2. Check to see there is a lock file, if so use the copy in memory for
   this 'connection'
   3. Check to see if the last modified date/time is newer then in memory,
   if so, load it, else use what is memory

Basically what I am looking for is the same basic connection pooling that
is implemented in the mod_dbd.  Is there an easy way to do this, or will I
simple need to get into the internals of the mod_dbd to figure out what it
is doing and do it myself.

Sam

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