[Koha-zebra] Perl Zoom Persistent Connections

[Sebastian Hammer]

Although as Mike points out, Z39.50 is a stateful protocol, it is often 
used in a non-stateful way in a web environment.

The PHP/YAZ 'persistent' connections means something a little different. 
Basically, it allows the webserver, when PHP is installed as a module, to 
keep connections open to the server between HTTP requests. This is a naive 
type of persistency, as the same connection may be shared among different 
users. However, it does potentially reduce the overheads associated with 
opening connections and initializing associations.. it is intended for use 
in applications with large numbers of transactions where it's useful to 
limit network traffic.. obviously, it does NOT work well if user-specific 
authentication is used against the server.

PHP/YAZ, in combination with the YAZ proxy, can be used to implement a more 
clever kind of persistency. It can actually keep user-specific sessions 
alive against a target, and associate each new incoming request with the 
right session based on a cookie. To this end, it uses an ID-specific 
extension to Z39.50, which is also supported by the YAZ/ZOOM (and YAZ/PHP) API.

--Sebastian

At 07:44 PM 8/19/2005 +0200, Thomas D wrote:
>PHP/YAZ was not written to use Zoom.  PHP/YAZ has persistent connections.
>
>Persistent connections are kept alive continuously and should not require
>reinitialisation of a new connection for each query, nor should they time
>out arbitrarily when the server determines your connection is inactive or
>becomes 'tired' of serving more results.
>
>yaz_connect() parameter options include persistent.
>
>This seems ussefull except for the problem of closing a persistent connection.
>
>"persistent"
>
>"    A boolean. If TRUE the connection is persistent; If FALSE the
>connection is not persistent. By default connections are persistent."
>
>"        Note: If you open a persistent connection, you won't be able to
>close it later with yaz_close()."
>
>Yaz_connect. PHP manual. The PHP Group. 2005.
>http://www.php.net/manual/en/function.yaz-connect.php .
>
>
>Thomas D
>
>
>Quoting Mike Taylor <mike at miketaylor.org.uk> :
> > ---------------- Beginning of the original message ------------------
> >
> > > Date: Fri, 19 Aug 2005 17:31:07 +0200
> > > From: Thomas D <koha at alinto.com>
> > >
> > > Will the forthcoming Perl bindings for Zoom support
> > persistent
> > > Z39.50 connections?
> >
> > Of course -- that is the only kind of Z39.50 connection.
> > Z39.50 is
> > not stateless like HTTP: all communication is of the form
> >
> >       open a connection
> >       while you're still interested {
> >               send a request
> >               wait for the response
> >               do something with it
> >       }
> >
> > > If there will be support for persistent connections, will
> > that
> > > support include a means to close those connections on
> > command;
> > > without killing the process from the shell, removing power
> > to the
> > > system or some other drastic measure [...]
> >
> > Yes, the $zoom->close() method will do this.
> >
> > > [...] as may be required for some existing Zoom bindings
> > with no
> > > means to close a persistent connection?
> >
> > There are none to my knowledge.  The ZOOM Abstract API
> > mandates a
> > Close method for Connection object -- see:
> >       http://zoom.z3950.org/api/zoom-1.4.html#3.2.6
> > and it is implemented (under the name
> > ZOOM_connection_destroy()) but
> > the ZOOM-C binding -- see:
> >       http://indexdata.com/yaz/doc/zoom.tkl#zoom.connections
> > and also by the current Perl implementation, the Net::Z3950
> > module --
> > see:
> >       http://perl.z3950.org/docs/Z3950/Connection.html#close()
> >
> > I am not quite sure what your question means ...
> >
> >  _/|_
> > ___________________________________________________________________
> > /o ) \/  Mike Taylor  <mike at miketaylor.org.uk>
> > http://www.miketaylor.org.uk
> > )_v__/\  "No one in charge of Christianity seems to be that
> > convinced
> >       about the product" -- Tim Rice.
> >
> >
> >
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>
>
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--
Sebastian Hammer, Index Data, www.indexdata.com
Direct phone: (603) 209-6853 Fax: (603) 357-1813