[OSM-dev] Complete history of OSM data - questions and discussion

[Tom Hughes]

On 12/11/09 16:28, Lars Francke wrote:

> I am partly done with my Java version. There are a few
> questions/problems/remarks:

Is Java really up to this job from a performance point of view?

> - Is there a dump of the database available from just prior to the
> switch from API 0.4 to 0.5? I could try to use that to merge the
> history of the segments to the ways (as briefly discussed by Frederik)

There is a dump, but it's a mysql dump so not easily readable. There may 
be a planet around somewhere as well but I don't think it will be 
synchronised to the actual shutdown time or have any history.

> - Any information on the size (in rows) of the tables would be nice
> (for testing purposes)

It should be fairly obvious for the main tables as they just contain a 
row for each object.

> - What is the default_statistics_target for the columns/tables in
> question? Are there any other options set that would affect the query
> planner? I've seen the query planner make wildly inappropriate
> decisions so I'll try to check if the statements I use will work. I
> used the same technique as planet.c and only adapted the queries to
> versions and history tables.

I'm not quite sure what you think knowing the value of that setting is 
going to help with. You only need to worry about optimising your queries 
if it turns out the planner gets them wrong but it's rarely a problem 
with Postgres especially with the kind of simple queries a dumper uses.

> - Do I have to take precautions in regards to database/machine/disk
> load? I could do something like the Auto-Vacuum daemon[2] or
> monitoring the load.

Auto vacuum is on by default these days I believe. It's not something an 
ordinary user has any control over anyway.

Tom

-- 
Tom Hughes (tom at compton.nu)
http://www.compton.nu/