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Re: memcached and PostgreSQL

From: Mike Rylander <mrylander(at)gmail(dot)com>
To: Greg Stark <gsstark(at)mit(dot)edu>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: memcached and PostgreSQL
Date: 2004-11-17 16:18:02
Message-ID: b918cf3d041117081859c17b9a@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On 17 Nov 2004 03:08:20 -0500, Greg Stark <gsstark(at)mit(dot)edu> wrote:
> Josh Berkus <josh(at)agliodbs(dot)com> writes:
> 
> > So memcached becomes a very good place to stick data that's read often but not
> > updated often, or alternately data that changes often but is disposable.   An
> > example of the former is a user+ACL list; and example of the latter is web
> > session information ... or simple materialized views.
> 
> I would like very much to use something like memcached for a materialized view
> I have. The problem is that I have to join it against other tables.
> 
> I've thought about providing a SRF in postgres to read records out of
> memcached but I'm unclear it would it really help at all.
> 
> Has anyone tried anything like this?

I haven't tried it yet, but I plan too.  An intersting case might be
to use plperlu to interface with memcached and store hashes in the
cache via some external process, like a CGI script.  Then just define
a TYPE for the perl SRF to return, and store the data as an array of
hashes with keys matching the TYPE.

A (perhaps useless) example could then be something like:

CREATE TYPE user_info AS ( sessionid TEXT,  userid INT, lastaccess
TIMESTAMP, lastrequest TEXT);

CREATE FUNCTION get_user_info_by_session ( TEXT) RETURNS SETOF user_info AS $$
  use Cache::Memcached;

  my $session = shift;

  my $c = $_SHARED{memcached} || Cache::Memcached->new( {servers =>
'127.0.0.1:1111'} );

  my $user_info = $m->get('web_access_list');

  # $user_info looks like
  # [ {userid => 5, lastrequest => 'http://...', lastaccess => localtime(),
  #    sessionid => '123456789'}, { ...} ]
  # and is stored by a CGI.

  @info = grep {$$_{sessionid} eq $session} @$user_info;

  return \(at)info;
$$ LANGUAGE 'plperlu';

SELECT u.username, f.lastrequest FROM users u,
get_user_info_by_session('123456789') WHERE f.userid = u.userid;


Any thoughts? 

> 
> --
> greg
> 
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-- 
Mike Rylander
mrylander(at)gmail(dot)com
GPLS -- PINES Development
Database Developer

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