[OSM-dev] Question: Tags key and value maximum length

Lars Francke lars.francke at gmail.com
Tue Apr 21 12:39:01 BST 2009

> The 255 limit is from MySQL. For the timebeing we are are trying to be
> compatible with MySQL for people who are still using MySQL. Many developers
> will not have had time to switch their development/production databases from
> MySQL to Postgres yet.

But MySQL must have a way to save text with more than 255 characters?
Found it: "Values in VARCHAR columns are variable-length strings. The
length can be specified as a value from 0 to 65,535. The effective
maximum length of a VARCHAR is subject to the maximum row size (65,535
bytes, which is shared among all columns) and the character set used."

> The limit also prevents problems of people putting huge amounts of data into
> them, thus causing problems elsewhere on the api, through huge documents
> being produced.

Well I can put houge amounts of data into multiple tags as well if I
really wanted. And to 'ban' one thing in the fear of it being misused
is in my opinion not the right way to go. I don't really want
unlimited size but an increase to something more sensible.

> If you want to put more than 255 chars, then you need to split it over
> multiple tags:
> description =
> description_1=
> description_2 =
> etc

Sorry but I think that is rather...well not the best way to go ;-)

I won't nag you any longer I just wanted to register my concerns and
to provide a (hopefully) valid point as to why a higher limit makes

Anyway: Thanks to all the people for their work on 0.6 and for the
"migration team" for the weekend work on the servers!


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