query performance - Mailing list pgsql-general

I have this query in a table with 150 thowsand tuples and it takes to long

    t_documentcontent._id AS _id
    FROM t_documentcontent LIMIT 50 OFFSET 80000

here is the explain output

"Limit  (cost= 100058762.30..100058799.02 rows=50 width=58) (actual time=19433.474..19433.680 rows=50 loops=1)"
"  ->  Seq Scan on t_documentcontent  (cost=100000000.00..100110772.07 rows=150807 width=58) (actual time=53.934..19402.030 rows=80050 loops=1)"
"Total runtime: 19433.748 ms"

here the table structure

CREATE TABLE t_documentcontent(
    _id varchar(60) NOT NULL,
    _filesystem varchar(60) NOT NULL,
    _parent varchar(60) NOT NULL,
    _document varchar(60) NOT NULL,
    _title varchar NOT NULL,
    _resume varchar,
    _content varchar,
    _lang integer NOT NULL,
    _creationdate timestamp NOT NULL DEFAULT now(),
    _updatedate timestamp NOT NULL DEFAULT now(),
    _indexeddate timestamp NOT NULL DEFAULT now(),
    CONSTRAINT documentcontent_pkey PRIMARY KEY (_id),
    CONSTRAINT documentcontent_filesystem_fkey
        FOREIGN KEY (_filesystem) REFERENCES t_filesystem(_id) ON UPDATE CASCADE ON DELETE NO ACTION,
    CONSTRAINT documentcontent_parent_fkey FOREIGN KEY (_parent) REFERENCES t_node(_id) ON DELETE NO ACTION,
    CONSTRAINT documentcontent_document_fkey
        FOREIGN KEY (_document) REFERENCES t_node(_id) ON UPDATE CASCADE ON DELETE NO ACTION,
    CONSTRAINT documentcontent_lang_lang_fkey FOREIGN KEY (_lang) REFERENCES t_lang(_id)) WITHOUT OIDS;

Any ideas for improve this query performance.