It is true that there are potentially better places to setup the hash,
but it is best to check for a null pointer
for the hash object anyway any time you use it. The setup itself is also
very fast; you just don't want to do
it every time. Note in my init function I forgot a 'hash = new hashc()'.
Also; if you are going to do this, you will likely have a preset list of
domains you are using.
In such a case, the best type of hash to use would be a 'minimal perfect
hash'.
You could use the 'gperf' library to generate a suitable algorithm to
map your domain strings
into an array.
On 3/7/2011 10:30 AM, AD wrote:
Cool, as for the startup, i wonder if you can instead of trying to
insert into VCL_Init, try to do just, as part of the startup process
hit a special URL to load the hash_Table. Or another possibility
might be to load an external module, and in there, populate the hash.
On Mon, Mar 7, 2011 at 9:45 AM, David Helkowski <[email protected]
<mailto:[email protected]>> wrote:
vcl configuration is turned straight into C first of all.
You can put your own C code in both the functions and globally.
When including headers/libraries, you essentially just have to
include the code globally.
I am not sure if there is any 'init' function when varnish is
called, so I was suggesting that
the hash be initiated by just checking if the hash has been
created yet.
This will cause a penalty to the first vcl_recv call that goes
through; but that shouldn't
matter.
Note that I just passed a dummy number as an example to the custom
config, and that
I didn't show how to do anything in the custom function. In this
example, all custom
stuff would be in straight C. You would need to use varnish itself
to compile what config
you want and look at the C code it generates to figure out how to
tie in all your custom
configs....
eg:
C{
#include "hash.c" // a string hashing store/lookup libary;
you'll need to write one
// or possibly just use some freely available one.
hashc *hash=0;
void init_hash() {
if( hash ) return;
hash.store( 'test.com <http://test.com>', &test_com );
// same for all domains
}
void test_com( int n ) {
// custom vcl_recv stuff for domain 'test'
}
}
sub vcl_recv {
C{
char *domain;
// [ place some code to fetch domain and put it in domain here ]
if( !hash ) init_hash();
void (*func)(int);
func = hash.lookup( domain );
func(1);
}
}
On 3/7/2011 9:23 AM, AD wrote:
but dont all the configs need to be loaded at runtime, not sure
the overhead here? I think what you mentioned seems like a
really innovative way to "call" the function but what about
anyimpact to "loading" all these configs?
If i understand what you are saying, i put a "call test_func;" in
vcl_recv which turned into this in C
if (VGC_function_test_func(sp))
return (1);
if
Are you suggesting your hash_table would take over this step ?
Adam
On Mon, Mar 7, 2011 at 8:02 AM, David Helkowski
<[email protected] <mailto:[email protected]>> wrote:
The best way would be to use a jump table.
By that, I mean to make multiple subroutines in C, and then
to jump to the different subroutines by looking
up pointers to the subroutines using a string hashing/lookup
system.
You would also need a flag to indicate whether the hash has
been 'initialized' yet as well.
The initialization would consist of storing function pointers
at the hash locations corresponding to each
of the domains.
I attempted to do this myself when I first started using
varnish, but I was having problems with varnish
crashing when attempting to use the code I wrote in C. There
may be limitations to the C code that can be
used.
On 3/6/2011 5:39 PM, AD wrote:
Hello,
what is the best way to run an instance of varnish that may
need different vcl configurations for each hostname. This
could end up being 100-500 includes to map to each hostname
and then a long if/then block based on the hostname. Is
there a more scalable way to deal with this? We have been
toying with running one large varnish instance with tons of
includes or possibly running multiple instances of varnish
(with the config broken up) or spreading the load across
different clusters (kind of like sharding) based on hostname
to keep the configuration simple.
Any best practices here? Are there any notes on the
performance impact of the size of the VCL or the amount of
if/then statements in vcl_recv to process a unique call
function ?
Thanks
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