• Article

sys.dm_os_memory_cache_clock_hands (Transact-SQL)

Returns the status of each hand for a specific cache clock.

Column name

Data type

Description

cache_address

varbinary(8)

Address of the cache associated with the clock. Is not nullable.

name

nvarchar(256)

Name of the cache. Is not nullable.

type

nvarchar(60)

Type of cache store. There can be several caches of the same type. Is not nullable.

clock_hand

nvarchar(60)

Type of hand. This is one of the following:

  • External

  • Internal

Is not nullable.

clock_status

nvarchar(60)

Status of the clock. This is one of the following:

  • Suspended

  • Running

Is not nullable.

rounds_count

bigint

Number of sweeps made through the cache to remove entries. Is not nullable.

removed_all_rounds_count

bigint

Number of entries removed by all sweeps. Is not nullable.

updated_last_round_count

bigint

Number of entries updated during the last sweep. Is not nullable.

removed_last_round_count

bigint

Number of entries removed during the last sweep. Is not nullable.

last_tick_time

bigint

Last time, in milliseconds, that the clock hand moved. Is not nullable.

round_start_time

bigint

Time, in milliseconds, of the previous sweep. Is not nullable.

last_round_start_time

bigint

Total time, in milliseconds, taken by the clock to complete the previous round. Is not nullable.

Permissions

Requires VIEW SERVER STATE permission on the server.

Remarks

SQL Server stores information in memory in a structure called a memory cache. The information in the cache can be data, index entries, compiled procedure plans, and a variety of other types of SQL Server information. To avoid re-creating the information, it is retained the memory cache as long as possible and is ordinarily removed from the cache when it is too old to be useful, or when the memory space is needed for new information. The process that removes old information is called a memory sweep. The memory sweep is a frequent activity, but is not continuous. A clock algorithm controls the sweep of the memory cache. Each clock can control several memory sweeps, which are called hands. The memory-cache clock hand is the current location of one of the hands of a memory sweep.