How do I retreive text very QUICKLY from the database ? . . .

Hey All,

I am trying to find a way to retreive character data from a table very
quickly.  My data is a large string (about 250 MB worth of text) of DNA
sequence.  I am currently storing the data as a Postgres "text" datatype.
The character data is in its own table and occupies one row and one column.

I would like to retreive a substring from this very long string.  I have
tried the built-in Postgres string functions to get a substring out from the
table, but it is too slow.  Is there a very fast way to retreive substrings
of character data from the database?

Does changing the datatype help (instead of using the "text" datatype)?

Thank you for any help.

Sincerely,
Peter