LOAD DATA INFILE decline in performance Query for insert:

LOCK TABLE tbl WRITE;
ALTER TABLE tbl DISABLE KEYS;
load data local infile "E:/One.txt" into table tbl fields terminated by "\t" lines terminated by "\n" (user_id, sexid, cityid);
ALTER TABLE tbl ENABLE KEYS;
UNLOCK TABLES;


First 5 million inserted per 2 min, second 3 million per 20 min, after 200k per min.
Why decline perfomance?
How to recover insertion speed?
~200 million of records.
Type table InnoDB
Indexes are not disabled in InnoDB using DISABLE INDEX
(from http://dev.mysql.com/doc/refman/5.1/en/alter-table.html):

For MyISAM tables, key updating can be controlled explicitly. Use
ALTER TABLE ... DISABLE KEYS to tell MySQL to stop updating nonunique
indexes. Then use ALTER TABLE ... ENABLE KEYS to re-create missing
indexes


For InnoDB, you're stuck with these hints: http://dev.mysql.com/doc/refman/5.5/en/optimizing-innodb-bulk-data-loading.html

I think you should also remove the indexes and re-create them after you populated the table (the same thing you tried to do with DISABLE/ENABLE KEYS)