defined max length

Hello ALL.

Where can I find (and set if need) all defined max length restrictions of PostgreSQL
server.
for example,
    max lenght of VARCHAR,
or any variable-length array,
or max query length and so on ?

I'm using PostgreSQL 7.2, RH linux 7.2


Thanks in advance.


--
Best regards,
 lexx                            mailto:lexx@gorodok.net