Information Schema INNODB_SYS_SEMAPHORE_WAITS Table

The INNODB_SYS_SEMAPHORE_WAITS table displays threads currently waiting for semaphores, which is useful for debugging high-concurrency contention.

The Information Schema INNODB_SYS_SEMAPHORE_WAITS table is meant to contain information about current semaphore waits. At present it is not correctly populated. See MDEV-21330.

The PROCESS privilege is required to view the table.

It contains the following columns:

Column	Description
THREAD_ID	Thread id waiting for semaphore
OBJECT_NAME	Semaphore name
FILE	File name where semaphore was requested
LINE	Line number on above file
WAIT_TIME	Wait time
WAIT_OBJECT
WAIT_TYPE	Object type (mutex, rw-lock)
HOLDER_THREAD_ID	Holder thread id
HOLDER_FILE	File name where semaphore was acquired
HOLDER_LINE	Line number for above
CREATED_FILE	Creation file name
CREATED_LINE	Line number for above
WRITER_THREAD	Last write request thread id
RESERVATION_MODE	Reservation mode (shared, exclusive)
READERS	Number of readers if only shared mode
WAITERS_FLAG	Flags
LOCK_WORD	Lock word (for developers)
LAST_READER_FILE	Removed
LAST_READER_LINE	Removed
LAST_WRITER_FILE	Last writer file name
LAST_WRITER_LINE	Above line number
OS_WAIT_COUNT	Wait count

_{This page is licensed: CC BY-SA / Gnu FDL}