[Dovecot] quick question

[Timo Sirainen]

On Fri, 2010-01-22 at 19:31 +0200, Timo Sirainen wrote:
> Better would be to have some kind of a database that externally monitors
> what servers are up and where users currently have connections, and
> based on that decide where to redirect a new connection. Although that's
> also slightly racy unless done carefully.

Wonder if something like this would work:

servers (
  id integer,
  host varchar,
  ip varchar,
  last_time_healty timestamp,
  connection_count integer,
  new_connections_ok boolean
);

user_connections (
  user_id integer primary key,
  server_id integer,
  last_lookup timestamp,
  imap_connections integer
);

Then some kind of logic that:

 - if user already exists in user_connections table AND
(imap_connections > 0 OR last_lookup>now() - 1 hour) use the old
server_id

 - otherwise figure out a new server for it based on servers'
connection_count and new_connections_ok.

 - when inserting, handle on duplicate key error

 - when updating, use update user_connections .. where user_id = $userid
and server_id = $old_server_id, and be prepared to handle when this
returns 0 rows updated.

Once in a while maybe clean up stale rows from user_connections. And
properly keeping track of imap_connections count might also be
problematic, so maybe once in a while somehow check from all servers if
the user actually still has any connections.
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