I've got a table structure that can be summarized as follows:

pagegroup
* pagegroupid
* name

has 3600 rows

page
* pageid
* pagegroupid
* data

references pagegroup; has 10000 rows; can have anything between 1-700 rows per pagegroup; the data column is of type mediumtext and the column contains 100k - 200kbytes data per row

userdata
* userdataid
* pageid
* column1
* column2
* column9

references page; has about 300,000 rows; can have about 1-50 rows per page

The above structure is pretty straight forwad, the problem is that that a join from userdata to page group is terribly, terribly slow even though I have indexed all columns that should be indexed. The time needed to run a query for such a join (userdata inner_join page inner_join pagegroup) exceeds 3 minutes. This is terribly slow considering the fact that I am not selecting the data column at all. Example of the query that takes too long:

SELECT userdata.column1, pagegroup.name
FROM userdata
INNER JOIN page USING( pageid )
INNER JOIN pagegroup USING( pagegroupid )

Please help by explaining why does it take so long and what can i do to make it faster.

Edit #1

Explain returns following gibberish:

id  select_type  table      type    possible_keys        key      key_len  ref                         rows    Extra
1   SIMPLE       userdata   ALL     pageid                                                             372420
1   SIMPLE       page       eq_ref  PRIMARY,pagegroupid  PRIMARY  4        topsecret.userdata.pageid   1
1   SIMPLE       pagegroup  eq_ref  PRIMARY              PRIMARY  4        topsecret.page.pagegroupid  1

Edit #2

SELECT
u.field2, p.pageid
FROM
userdata u
INNER JOIN page p ON u.pageid = p.pageid;
/*
0.07 sec execution, 6.05 sec fecth
*/

id  select_type  table  type    possible_keys  key      key_len  ref                rows     Extra
1   SIMPLE       u      ALL     pageid                                              372420
1   SIMPLE       p      eq_ref  PRIMARY        PRIMARY  4        topsecret.u.pageid 1        Using index

SELECT
p.pageid, g.pagegroupid
FROM
page p
INNER JOIN pagegroup g ON p.pagegroupid = g.pagegroupid;
/*
9.37 sec execution, 60.0 sec fetch
*/

id  select_type  table  type   possible_keys  key          key_len  ref                      rows  Extra
1   SIMPLE       g      index  PRIMARY        PRIMARY      4                                 3646  Using index
1   SIMPLE       p      ref    pagegroupid    pagegroupid  5        topsecret.g.pagegroupid  3     Using where

Moral of the story

Keep medium/long text columns in a separate table if you run into performance problems such as this one.