writing CGI::Session sessions only when necessary

[Jonathan Swartz <SW...@POBOX.COM>]

On our site we create a new CGI::Session object at the beginning of  
the request, so that it can be used anywhere in the web code.

However, sessions are rarely written to, so at the end of the request  
I'd like to avoid actually writing out a new session to backing store  
unless a param actually got set. The expense of writing out new  
sessions, and cleaning them up later, has become significant.

I couldn't figure out a way to do this with the public CGI::Session  
API, but I managed to get it to work this way:

    1   my $session = CGI::Session->new(...);
    2   $session->_unset_status(CGI::Session::STATUS_MODIFIED);
    3
    4   # ... web code gets executed here ...
    5
    6   if (!$session->_test_status(CGI::Session::STATUS_MODIFIED)) {
    7       $session->_reset_status;
    8   }
    9   $session->flush();

I initially reset the modified bit on line 2. Then on line 6, if the  
modified bit is still unset (meaning no param was ever set), I clear  
the status entirely, which causes the flush() on line 9 to be a no-op.

Is there a better, e.g. supported, way to do this? How do other people  
prevent new sessions from getting written to the backing store  
unnecessarily?

Thanks
Jon

Re: writing CGI::Session sessions only when necessary

[Jonathan Swartz <SW...@pobox.com>]

On Jan 27, 2010, at 2:45 PM, Perrin Harkins wrote:

> On Tue, Jan 26, 2010 at 7:42 PM, Jonathan Swartz <SW...@pobox.com>  
> wrote:
>> On our site we create a new CGI::Session object at the beginning of  
>> the
>> request, so that it can be used anywhere in the web code.
>>
>> However, sessions are rarely written to, so at the end of the  
>> request I'd
>> like to avoid actually writing out a new session to backing store  
>> unless a
>> param actually got set.
>
> It might be simpler to just write immediately when you set a param.
> It's simple and foolproof, and it's only a negative for performance if
> you normally set multiple params in a single request.
>
> If your ultimate goal is to fix performance on your servers, I'd
> recommend looking at using encrypted data in a cookie and ditching
> server-side session storage.
>

True. My solution only involves a couple of lines of code, so it isn't  
going to get much simpler. It would just be ideal if I could use the  
public API. And this seems like an optimization that others might want.

Re: writing CGI::Session sessions only when necessary

[Perrin Harkins <ph...@gmail.com>]

On Tue, Jan 26, 2010 at 7:42 PM, Jonathan Swartz <SW...@pobox.com> wrote:
> On our site we create a new CGI::Session object at the beginning of the
> request, so that it can be used anywhere in the web code.
>
> However, sessions are rarely written to, so at the end of the request I'd
> like to avoid actually writing out a new session to backing store unless a
> param actually got set.

It might be simpler to just write immediately when you set a param.
It's simple and foolproof, and it's only a negative for performance if
you normally set multiple params in a single request.

If your ultimate goal is to fix performance on your servers, I'd
recommend looking at using encrypted data in a cookie and ditching
server-side session storage.

- Perrin