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From "David Wortham" <>
Subject Re: load data at server startup - is ap_hook_post_config() the right place?
Date Fri, 23 Mar 2007 23:25:05 GMT
   My recommendations (some of which are off topic for this list):
(1) If you are almost done with the module, why not go ahead and test to see
if each child process is getting a unique copy of the server_config_struct?
It is possible that if you never try to write to that data after server
startup (i.e. from a request handling function or a filter function) that
you will see many/all of the child processes using the same
server_config_struct (printf the struct as an integer using "%d"... that
will give you an integer representation of the struct's memory location).
There may be no problem (or you may see that the total RAM consumed is
(2) Try not using a server_config_struct merge  function.  If your child
process doesn't write to the server_config_struct (possibly only done by the
merge function).
(3) Have you considered using a single Apache server with only a list of
mod_proxy directives to act as the load balancer?  I'm not saying this is
the best way to go, but this may help you distribute your VHosts and
directories the way you want (Perhaps faster than you think).  Do a search
for pages containing both mod_rewrite and mod_proxy if you are unfamiliar
with this technique. (I'm not sure this technique works with fully redundant
servers and/or directories).
(4) You may save programming time by calling a PERL/PHP/otehr_language
script to update a file from your DB SELECT statement.  Call your script
before httpd start|restart|stop.  Then all you have to do to update your
server_config_struct is to unserialize the file into your struct.

If each of your 10~20 servers are identical (all contain all VHosts and all
directories) then your current layout may be one of the optimal schemes
(given the extreme redundancy).
However, (I don't know the particulars of your requirements, but) I would
think you could have the main Apache server (which receives ALL initial
requests and loadbalances) distribute the requests by domain.  That server
should hand off requests to one of, say, 4 servers.  These 4 servers should
further load-balance to 4 other servers (which can include itself) based on
a combination of the domain/directory (giving you a 1-4-4 tree).
You may run into weird session problems (including problems with the
loadbalancer) if you are sending the same visitor to two different
end-Apache servers with the same MX/domain based on different directories,
you may run into session problems (I'm not speaking from experience, just


On 3/23/07, Danie Qian <> wrote:
> ----- Original Message -----
> From: "David Wortham" <>
> To: <>; "Danie Qian" <>
> Sent: Friday, March 23, 2007 2:39 PM
> Subject: Re: load data at server startup - is ap_hook_post_config() the
> right place?
> > Daniel,
> >    AFAIK, "mutex" refers to mutual exclusion.  It is commonly referred
> to
> > in relation to multi-threading but can apply to an inter-process scheme
> > too.  I would assume that only one thread of one (child) process can
> > access
> > a given resource at a given time, but you should refer to the
> > documentation
> > of any code you use for those specifics.  I'm sorry, but I don't have
> any
> > personal experience with mutex and the APR libs.
> >
> >   Are you talking about adjusting your Apache child/thread setup for
> > development or are you targeting your module to only Apache
> installations
> > with specific configuration (i.e. single-thread mode)?
> > If you are worried about the size of a child process'
> > server_config_struct,
> > you could just program it to take a lot of room in the
> > server_config_struct
> > and recommend that Apache be configured for only one child-process.  I
> > would
> > recommend against it, but it doesn't seem like a terrible idea.  There
> > will
> > probably be significant performance hits on certain
> > OSes/Apache-deployments
> > (*NIX) and less on others (likely WinNT since I believe it defaults to a
> > single-child process with a large thread-count).
> >
> >   Also, what are you using this giant list of URIs for?  There may be a
> > more efficient way of distributing the processing load (and, therefore,
> > speeding up the overall Apache response time).  If I read your first
> post
> > to
> > this list correctly, you are using a table (as in apr_table_*, a DB
> table,
> > or other?) with a large number of URLs.  You aren't walking through a
> > sequential list of URLs in apr_tables are you?  Are the "URI"s you're
> > storing full URIs, domain names, or MXs?  Perhaps you could use some
> help
> > with your overall design of the module (or maybe there's an existing
> > module
> > that does what you want).
> >
> Hi Dave,
> To be more meaningful about what I am talking about, here is our setup: We
> have around 5 thousand sites running on a few web-farmed locations. Each
> location has about 10~20 linux apache servers running behind a load
> balancer. Every apache usually has 40~50 child processes running to serve
> the amount traffic. Internally every site is maintained as one of our
> products with all its operation information stored in mysql databases.
> With
> the information from one of the tables we can decide where the site folder
> is by looking at the site name and some other fields associated with the
> site. What I am thinking to do with the module is to load all the relevant
> fields into apache memory space upon apache startup and let every request
> look up from that chunk of memory for better performance. so as u can see
> we
> are nailed a setup of multiple processes and probably single thread mode
> in
> apache.
> Thanks,
> Daniel

David Wortham
Senior Web Applications Developer
Unspam Technologies, Inc.
1901 Prospector Dr. #30
Park City, UT 84060
(435) 513-0672

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