[mkgmap-dev] [PATCH v1] Reduce memory footprint of tags

Mon Feb 8 20:59:29 GMT 2010

Hi

> method. This ensures that the String "highway" exists only once when
> stored as tag. Additionally the values of the most common tags with a
> limited number of different values are also interned. (It makes sense to
> intern the value of a highway tag but it does not make sense to intern
> the value of a name tag because the share rate of the name tag values is
> too low).
>
> This all might sound embarrasing but the String objects that are
> returned from the XML reader are not interned. You can test this easily
> by exchanging the put method in class tag:

> I have seen memory reductions of > 10%.

This is all very true.

In fact the patch on the style-speed branch sneakily does an equivalent 
thing to itern'ing the key values, which does indeed save a lot of
memory.  So we do not need to add intern() inside Tags.put

The intern on the values has less effect but might be still worth doing.

..Steve