Databases Reference
In-Depth Information
and be comfortable with the output they provide. In addition, s
ys.dm_os_waiting_tasks
will
display a list of any tasks that are currently waiting on a resource, providing a useful
session_id
column that can be used to hook into other useful DMVs for information about sessions and
the like.
sys.dm_os_wait_stats
This DMV has i ve columns.
➤
wait_type
➤
waiting_tasks_count
➤
wait_time_ms
➤
max_wait_time_ms
➤
signal_wait_time_ms
The i rst three were described earlier.
max_wait_time_ms
shows the largest wait time for a single
wait since the DMV was cleared.
signal_wait_time_ms
is less relevant for latches, although it does
get used if threads hit spinlock barriers.
sys.dm_os_latch_stats
This DMV has four columns.
➤
latch_class
➤
waiting_requests_count
➤
wait_time_ms
➤
max_wait_time_ms
These columns have all been described earlier.
sys.dm_os_spinlock_stats
This DMV has six columns.
➤
name
➤
collisions
➤
spins
➤
spins_per_collision
➤
sleep_time
➤
backoffs
A collision is recorded when a spinlock tries to acquire a resource but i nds it unavailable. As a
result, the spinlock starts spinning. This increases the spins but the collision has already been
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