[OSM-dev] Is there a way to use simple schema without hstore

Brett Henderson brett at bretth.com
Sat Nov 20 00:38:33 GMT 2010


On Fri, Nov 19, 2010 at 7:37 PM, Andreas Kalsch <andreaskalsch at gmx.de>wrote:

>  Hi Brett,
>
> thanks for your elaborate answer! Now I am up to date. Some ideas regarding
> my use case ...
>
> Am 18.11.10 23:50, schrieb Brett Henderson:
>
> Hi Andreas,
>
> The change was made mostly for performance reasons.  With a full planet
> imported into the database, bounding box style queries are now approximately
> 10 times faster.  This is due to a couple of reasons:
>
>    - All data (with the exception of relations) is now clustered by
>    geographical location.  This drastically improves performance where data is
>    being processed for a limited area.
>    - The nodes and ways tables are the only tables that have a geometry
>    column, thus other data must be embedded in those tables in order to make
>    use of clustering.
>
>  My concept is always to use _1_ table for all geometries and to create
> extractions when I need them. Because a geom column can store any type, so
> it is a more unifying concept.
>

I'm not following.  Are you suggesting that node and way tables be merged?


>
> I don't understand your comment regarding NoSQL.  The main change is that
> now you will have to deal with a more complex hstore column type on the
> nodes/ways tables, but otherwise the same data still exists and can still be
> manipulated with SQL statements.  The data is less relational that it was
> previously, but tag data is not terribly useful without access to parent
> entities so grouping them together shouldn't result in loss of
> functionality.
>
>
> You can still populate separate tags tables if you wish by running your own
> separate query to pull the hstore column apart.
>
> This is what I need to do sooner or later, when I will update. It's
> important for me to use a separate table for tags, because I run a script
> that will correct the tags of relations (from outer ways to relations), and
> I don't want to rewrite this and other scripts that depend on this schema
> every time the version changes.
> Running an extra script that fetches the hstore tags and puts them into a
> separate table will add the time that PBF gave me ;(
> My main concern is that with the next big schema update I _have_ to patch
> the schema. On the long run it is great to be conservative about such
> changes or *)
>

My best suggestion is to continue running the old Osmosis.  The old version
still works so don't upgrade.  As Frederik suggests you can run the two
versions alongside each other and pipe data between them as necessary.


>
>
> If you're applying diffs to the database you can enhance the
> osmosisUpdate() function (initially empty, but can be customised) to keep
> your separate tags tables up to date during each diff application.  You will
> need to run the "pgsql_simple_schema_0.6_action.sql" script against the
> database so that all actions during a diff are logged and can be used by
> your osmosisUpdate function to know which records need to be re-processed.
>
> Is it possible to truncate the actions table for myself so that a separate
> script can access the changes?
>
> This is another important point. In the moment, I manually populate my own
> "current_features" tables after an update that are populated with all
> features, whose tstamp is >= the time of the last update. A little overhead
> ... I see that this table exists in 0.36 as well, so I could use it, if I
> can truncate it manually?
>

As Sarah suggests, the way to do this is to create your own table and
populate it from the actions table within the osmosisUpdate function.  The
overhead in doing this should be relatively small.


>
> The older Osmosis 0.36 is still available so you don't have to upgrade.  It
> remains compatible with 0.6 XML files.  Finally, if there is enough demand
> for the older schema style the old tasks can be pulled back out of SVN and
> run alongside the new ones, but I'm not keen to do that without good
> reason.  I did consider trying to support both styles of table in the same
> tasks by dynamically detecting what tables are installed, but it increases
> the code complexity considerably and I didn't think the effort was
> worthwhile.
>
> *) With that, you would provide a downward compatible solution that I would
> appreciate a lot!
>

I'm hesitant to do this for one person's use case.  I don't mean to be
unhelpful, but I have to be very careful about where spend my limited time
on Osmosis and for this reason I try to keep things as simple as possible.
That sometimes means removing old obsolete functionality and breaking
compatibility from time to time.

Can you make do with the older version for now?  If enough demand comes up
for the old style schema then I'll look into it.  Alternatively I'm always
happy to accept a patch :-)


>
> Is it necessary that Osmosis makes the schema checks? What about giving
> each schema a unique ID and then let the user point Osmosis to this ID and
> let it fail, if the user has installed the wrong schema?
>

I don't understand your suggestion.  The schema currently has a schema_info
which contains a version number, that is all.  It fails if the wrong version
is detected.  But you can tell it to ignore the schema version with
validateSchemaVersion=no where it will blindly attempt to use the schema and
fail if it can't find the tables/columns it needs.

Brett
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