fe_locks

fe_locks provides information about metadata locks in StarRocks FE. It is one of the system-defined views in the sys database.

The following fields are provided in fe_locks:

Field	Description
lock_type	Type of the lock (e.g., "DATABASE").
lock_object	Object identifier that is locked (database name, table name, etc.).
lock_mode	Lock mode. Valid values: EXCLUSIVE, SHARED.
start_time	When the lock was acquired.
hold_time_ms	Duration the lock has been held (in milliseconds).
thread_info	JSON string containing thread information (threadId, threadName).
granted	Whether the lock is currently granted.
waiter_list	Comma-separated list of threads waiting for this lock.

Lock Modes

• EXCLUSIVE: Only one thread can hold this lock at a time.
• SHARED: Multiple threads can hold this lock simultaneously.

Lock Types

• DATABASE: Database-level locks.
• TABLE: Table-level locks.

StarRocks manages metadata locks through the Lock Manager, which provides centralized lock management with table-level granularity.

Examples

Find long-running locks

SELECT lock_object, lock_mode, hold_time_ms, thread_info
FROM sys.fe_locks 
WHERE hold_time_ms > 10000  -- Locks held for more than 10 seconds
ORDER BY hold_time_ms DESC;

Check for lock contention

SELECT lock_object, COUNT(*) as lock_count
FROM sys.fe_locks 
WHERE granted = true
GROUP BY lock_object
HAVING COUNT(*) > 1;

Find waiting threads

SELECT lock_object, waiter_list
FROM sys.fe_locks 
WHERE waiter_list != '';

Notes

• Querying fe_locks requires OPERATE privilege.
• The view provides real-time information but may impact performance on systems with high lock activity.
• Use appropriate WHERE clauses to filter results when dealing with large numbers of locks.