Which AWS database services are designed for storing logging records like log4j or log4perl?
Since you're looking at storing and querying 135,000,000 * 30 * 10 records that likely wouldn't benefit from traditional RDBMS features, I think Hadoop would be the way to go.

My experience is exclusively with Microsoft Azure - if you're not attached to Amazon you might check it out. Either way, Hadoop is open source so the majority of operations and activity should be the same regardless of your platform provider. I'd go with an option that allows you to test the performance of different cluster sizes so you're only paying for what you really need (especially with the 10x increase as an unknown right now).

The following link, despite its Azure focus, gives you a good tutorial of how to query log4j records with Hive. Amazon EMR appears to have great documentation.

Key points for your situation:
Create a table structure over your files:

    CREATE EXTERNAL TABLE log4jLogs
    (t1 string, t2 string, t3 string, t4 string, t5 string, t6 string, t7 string)
    ROW FORMAT DELIMITED FIELDS TERMINATED BY ';'
    STORED AS TEXTFILE LOCATION 'yourdrive:///logs/';


With the table defined you can then query similar to SQL:

    SELECT t4 AS sev, COUNT(*) AS ErrorCount
    FROM log4jLogs
    WHERE t4 = '[ERROR]'
    AND INPUT__FILE__NAME LIKE '%.log' GROUP BY t4;


With the EXTERNAL definition you can have multiple files and the table will include them all, so just drop them in the appropriate directory. If you're keeping 30 days worth you may want to get fancier and separate days into different folder structures/partition your Hive table.