I write on Perl/bash for Linux systems.
Worked with mysql: administration (backup, master-slave replication), some query optimization, DB-schema optimization, big-tables (up to 10 millions records in table), InnoDB/MyISAM tables, etc.
Have experience in web-scraping.
Worked with xml/excel-files parsing, Google Analytics (only programming, not optimizations).
Know a little PostgreSQL, php, python.