[OSM-talk] live rendering

[Lester Caine]

Robert (Jamie) Munro wrote:
> I agree with the spool file idea. This is the only sensible way to do
> the global RSS feed, for example. Of course, one good way to implement
> the spool file is as a table in the DB that is updated with triggers :-)
> (see http://fibre.sf.net/ for my generic DB replication system that does
> just that)
> 
> OTOH, I'm not sure that the intensity of write access is the problem we
> have. I think (but this is only a hunch) the writing problems are mostly
> due to things being locked by the read operations. PostGres would remove
> these issues with it's MGA architecture.

Now you are right in my area :)
FiBRE is just one of the Firebird facilities that allow for load sharing 
without the need to go to the big boy databases. Firebird has always had MGA, 
triggers and UDF's, and for systems that require the sort of capacity that OSM 
already needs it has all the tools in place. Posgres is slowly catching up on 
THAT side of things - but I have to admit that Posgres has concentrated on 
areas like PostGIS instead.

Since we do not need to worry about licences for multiple systems, spreading 
the load across multiple machines is a doddle. All the writes to the system 
should be done to one machine, and once data is verified it is replicated out 
to multiple read servers. The replication data log is also the update script 
for remote copies of the data.

Triggers are added to the master server to carry out such operations as 
converting raw text into entries in secondary tables. We can maintain all of 
the 'free form' capabilities, but rather than storing every single copy of 
'secondary', these are converted into tags in a text table, and the triggers 
do all the conversion work. Automatically converting 'place=x','name=y' into a 
nice cross referenced location table is almost free!

-- 
Lester Caine - G8HFL
-----------------------------
Contact - http://home.lsces.co.uk/lsces/wiki/?page=contact
L.S.Caine Electronic Services - http://home.lsces.co.uk
MEDW - http://home.lsces.co.uk/ModelEngineersDigitalWorkshop/
Firebird Foundation Inc. - http://www.firebirdsql.org/index.php