See who is blocking whom.

How it works

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• Each row is a waiting session and the session it waits for.
• A root blocker blocks others but is not blocked itself. Ending a session in the middle of a chain fixes nothing.
• A root blocker that is missing from your rows is usually idle with an open transaction. It holds locks without running anything, so blocking queries don't list it as a request.
• Sessions that wait for each other in a loop are a deadlock.

Queries that produce the right output

• SQL Server: step 1 of How to find what's blocking in SQL Server, or sp_who2.
• PostgreSQL: step 1 of How to find blocking and deadlocks in PostgreSQL.
• MySQL 8: SELECT waiting_pid, blocking_pid, waiting_query FROM sys.innodb_lock_waits;