[mkgmap-dev] Out of heap space: Too many tags?

Wed Feb 25 07:04:13 GMT 2009

On Tue, 24 Feb 2009, Steve Ratcliffe wrote:

> On Tue, Feb 24, 2009 at 10:17:47PM +0100, Wolfgang v. Hansen wrote:
>> I just tried to compile a relatively small tile and got an out of 
>> memory error from Java! [...] The number of tags is ten times the 
>> number of nodes in the file.
>
> The typical ratio in the UK seems to be about the same number or slightly
> more tags as nodes.  So ten times is a lot.  In places where there
> have been data imports it is probably more normal to have large numbers
> of tags though.
>
> Normally the number of nodes determines the amount of memory needed, but
> if there are so many more tags then they will indeed require even more
> memory.

So I was right. Obviously these were all addresses so it might well be 
possible that tags might dominate the planet.osm in the future. In 
addition, as tags are the free-style way to add information, many of them 
will not be recognized by a particular software such as mkgmap.

Is it feasible to filter the tags while reading the file? One could 
ingnore unknown tags entirely and convert the known ones to a (compressed) 
internal representation.

-Wolfgang