Cheatsheet

I have always neglected to write down java tools and commands that I use for troubleshooting. I will try to put in on this page. Memory and Threads There are many tools to measure java memory. In my experience, the easiest way to troubleshoot locally is to hook your development environment up to VisualVM. There are even plugins for it in e.g. IntelliJ. It is probably possible to do this to a production server as well, but that would likely impact performance. If you have access to the server, and have nothing prepared, you can do a heap-dump, which you can copy over and analyze in your local VisualVM. Taking heap dumps is done by jcmd 1 GC.heap_dump /tmp/dump.hprof. ...

Collection of powershell stuff. Curl replacement Invoke-WebRequest -Uri http://localhost Invoke-WebRequest -Uri http://localhost -Method POST $cred = Get-Credential Invoke-WebRequest -Uri http://localhost -Method POST -Credential $cred -UseBasicParsing

Starting mysql # Same username, no password mysql -p # Password protected mysql -u user mysql -h hostname Create user CREATE USER me GRANT ALL PRIVILEGES ON database_name.* TO 'me'@'%'; ALTER USER 'me'@'%' IDENTIFIED BY 'newPass'; Connect to databaes SHOW DATABASES; SHOW DATABASES LIKE 'ok%'; USE mysql; See database tables SHOW TABLES; SHOW TABLES LIKE 'ok%'; SELECT * FROM important_stuffs; Extend tables ALTER TABLE important_stuffs ADD description VARCHAR(100); ALTER TABLE important_stuffs ADD description VARCHAR(100) AFTER severity; ALTER TABLE important_stuffs ADD description VARCHAR(100) FIRST; Delete from tables SELECT * FROM important_stuffs WHERE severity="low"; DELETE FROM important_stuffs WHERE severity="low"; Insert into tables INSERT INTO important_stuffs VALUES("Wow, so important", "high"); INSERT INTO important_stuffs SET description="Wow, so important", severity="high"; Show access rights SHOW GRANTS; Change all email addresses to my (when mailserver is activated) UPDATE users SET email= CONCAT('me+', id, '@iix.se'); General log show variables like 'general_log%'; SET GLOBAL general_log = 'ON'; SET GLOBAL general_log = 'OFF'; Run query without cache SELECT SQL_NO_CACHE * from users where name like 'Ol%'; Indexes SHOW INDEX FROM users; ALTER TABLE users ADD INDEX index_name(firstName); CREATE INDEX index_name ON users(firstName); ALTER TABLE users DROP INDEX users; DROP INDEX index_name ON users; Explain/describe EXPLAIN users; DESCRIBE users; DESC users; DESC SELECT * FROM users; Profiling SET SESSION profiling = 1; SHOW PROFILES; SHOW PROFILE FOR QUERY 3; SHOW STATUS LIKE 'Last_Query_Cost'; Collation show variables like "collation_database"; SELECT SCHEMA_NAME 'database', default_character_set_name 'charset', DEFAULT_COLLATION_NAME 'collation' FROM information_schema.SCHEMATA;