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📎 #deadlock #sql #mysql
innodb_semaphore_metrics
SHOW ENGINE INNODB STATUS; study
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SEMAPHORES
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OS WAIT ARRAY INFO: reservation count 9441065
OS WAIT ARRAY INFO: signal count 8293591
RW-shared spins 0, rounds 29778623, OS waits 5644464
RW-excl spins 0, rounds 52192763, OS waits 846515
RW-sx spins 102704, rounds 1242783, OS waits 15699
Spin rounds per wait: 29778623.00 RW-shared, 52192763.00 RW-excl, 12.10 RW-sx
OS WAIT ARRAY INFO
| Term | Description |
|---|---|
reservation count | number of times threads have reserved a spot |
signal count | number of times threads have been signalled |
Sempaphores
| Sempaphore type | Description |
|---|---|
RW-shared | used for shared access (read) |
RW-excl | used for exclusive access (write) |
RW-sx | for special case where thread upgrades from shared to exclusive access |
| Metric | Description |
|---|---|
spins | number of times a thread has "spun" (busy-waited) while trying to acquire the semaphore |
rounds | total number of times threads have attempted to acquire the semaphore |
OS waits | number of times threads have had to wait in OS's wait queue because semaphore not available |
Spin rounds per wait | The average number of spin attempts before resorting to an OS wait |