Will redirecting queries to dev/null warm up indexes?
I see one of the comments in the question mentions caching indexes


  please note that only one index will be cached in the buffer pool (most probably PRIMARY, but check EXPLAIN to be sure). You may need secondary indexes in the cache as well, so you have to run additional SELECTs


It just so happens I have post from Feb 04, 2012 that lets you make those queries (MySQL warm procedure). From that post, here are the queries to show all queries you need to run:

LOADING INNODB BUFFER POOL

SELECT DISTINCT
    CONCAT('SELECT ',ndxcollist,' FROM ',db,'.',tb,
    ' ORDER BY ',ndxcollist,';') SelectQueryToLoadCache
    FROM
    (
        SELECT
            engine,table_schema db,table_name tb,
            index_name,GROUP_CONCAT(column_name ORDER BY seq_in_index) ndxcollist
        FROM
        (
            SELECT
                B.engine,A.table_schema,A.table_name,
                A.index_name,A.column_name,A.seq_in_index
            FROM
                information_schema.statistics A INNER JOIN
                (
                    SELECT engine,table_schema,table_name
                    FROM information_schema.tables WHERE
                    engine='InnoDB'
                ) B USING (table_schema,table_name)
            WHERE B.table_schema NOT IN ('information_schema','mysql')
            ORDER BY table_schema,table_name,index_name,seq_in_index
        ) A
        GROUP BY table_schema,table_name,index_name
    ) AA
ORDER BY db,tb


LOADING MyISAM KEY CACHE

SELECT DISTINCT CONCAT('SELECT ',ndxcollist,' FROM ',db,'.',tb,' ORDER 
BY ',ndxcollist,';') SelectQueryToLoadCache
FROM (SELECT engine,table_schema db,table_name tb,index_name,
GROUP_CONCAT(column_name ORDER BY seq_in_index) ndxcollist
FROM (SELECT 
B.engine,A.table_schema,A.table_name,A.index_name,A.column_name,A.seq_in_index
FROM information_schema.statistics A INNER JOIN
(SELECT engine,table_schema,table_name
FROM information_schema.tables
WHERE engine='MyISAM' AND table_schema
NOT IN ('information_schema','mysql')) B
USING (table_schema,table_name)
WHERE A.index_type &lt;&gt; 'FULLTEXT'
ORDER BY table_schema,table_name,index_name,seq_in_index) A
GROUP BY table_schema,table_name,index_name) AA
ORDER BY db,tb
;


LOADING INNODB BUFFER POOL AND MyISAM KEY CACHE

SELECT DISTINCT
    CONCAT('SELECT ',ndxcollist,' FROM ',
    db,'.',tb,' ORDER BY ',ndxcollist,';') SelectQueryToLoadCache
FROM (
    SELECT
        engine,table_schema db,table_name tb,index_name,
        GROUP_CONCAT(column_name ORDER BY seq_in_index) ndxcollist
    FROM (
        SELECT
            B.engine,A.table_schema,A.table_name,
            A.index_name,A.column_name,A.seq_in_index
        FROM
            information_schema.statistics A INNER JOIN
            (
                SELECT engine,table_schema,table_name
                FROM information_schema.tables
                WHERE engine IN ('InnoDB','MyISAM')
            ) B USING (table_schema,table_name)
        WHERE
            B.table_schema NOT IN ('information_schema','mysql')
            AND A.index_type &lt;&gt; 'FULLTEXT'
        ORDER BY
            table_schema,table_name,index_name,seq_in_index
        ) A
    GROUP BY
        table_schema,table_name,index_name
) AA
ORDER BY
    engine DESC,db,tb
;


Simply redirect the output to a text file like /root/IndexWarmup.sql

Then, login to mysql and run

mysql&gt; source /root/IndexWarmup.sql


OPTIONAL SUGGESTION

I would highly recommend upgrading to MySQL 5.6. Why? You can do the following:

Dump and Load a map of the InnoDB Buffer Pool Shutdown and Startup

[mysqld]
innodb_buffer_pool_dump_at_shutdown=1
innodb_buffer_pool_load_at_startup=1


Dump and Load a map of the InnoDB Buffer Pool on Demand

mysql&gt; set global innodb_buffer_pool_dump_now = 1;
mysql&gt; set global innodb_buffer_pool_load_now = 1;


That way, you never have to read index pages into the Buffer Pool you never access.

Please see the MySQL Documentation


innodb_buffer_pool_dump_at_shutdown
innodb_buffer_pool_load_at_startup
innodb_buffer_pool_dump_now
innodb_buffer_pool_load_now