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From Perrin Harkins <>
Subject Re: Persisting data across authenticate <-> authorize ?
Date Mon, 13 Dec 2004 20:10:39 GMT
On Mon, 2004-12-13 at 12:58 -0700, Tim Pushor wrote:
> For example, what I need to do (at a high level) is be able to add 
> entries to the cache with a minimum TTL, and be able to have the ability 
> to reset the TTL on individual entries as need be.

Anything with individual TTL settings per item will let you do this.

> >In what way?  BerkeleyDB can handle tremendous amounts of data, and the
> >locking is more efficient than what IPC::Shareable uses.
> >
> >  
> >
> Perhaps - I just think that there has to be a more efficient way of 
> sharing data between processes than writing it to disk.

It doesn't normally go to disk with BerkeleyDB.  There's a shared memory
cache.  Even things that just use the filesystem are really not going to
disk on Linux, since they are effectively using the VM system as shared

> The module I 
> wrote was for a busy community type site where all access was 
> authenticated, so I spread the data across multiple db's to reduce lock 
> contention.

Page-level locking would probably work better than that, but in my
experience I never found the file-level locking in BerkeleyDB's simple
mode to be an issue.

> To really be honest, I have never really used shared memory 
> much (in any programming language) so I don't really understand the main 
> issues - but I thought locking (in the perl module) was done with 
> semaphores...

I don't know how BerkeleyDB implements it, but it's in the C code, not
in the Perl code.

The real problem with shared memory things like IPC::Shareable is that
they have to serialize and de-serialize your entire data structure using
Storable every time you read or write it.  They have no way to address
individual entries.  The fast modules handle entries individually.

- Perrin

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