sys.dm_os_memory_cache_clock_hands (Transact-SQL)


THIS TOPIC APPLIES TO:yesSQL Server (starting with 2008)noAzure SQL DatabaseyesAzure SQL Data Warehouse yesParallel Data Warehouse

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

System_CAPS_ICON_note.jpg Note

To call this from Azure SQL Data Warehouse or Parallel Data Warehouse, use the name sys.dm_pdw_nodes_os_memory_cache_clock_hands.

Column nameData typeDescription
cache_addressvarbinary(8)Address of the cache associated with the clock. Is not nullable.
namenvarchar(256)Name of the cache. Is not nullable.
typenvarchar(60)Type of cache store. There can be several caches of the same type. Is not nullable.
clock_handnvarchar(60)Type of hand. This is one of the following:



Is not nullable.
clock_statusnvarchar(60)Status of the clock. This is one of the following:



Is not nullable.
rounds_countbigintNumber of sweeps made through the cache to remove entries. Is not nullable.
removed_all_rounds_countbigintNumber of entries removed by all sweeps. Is not nullable.
updated_last_round_countbigintNumber of entries updated during the last sweep. Is not nullable.
removed_last_round_countbigintNumber of entries removed during the last sweep. Is not nullable.
last_tick_timebigintLast time, in milliseconds, that the clock hand moved. Is not nullable.
round_start_timebigintTime, in milliseconds, of the previous sweep. Is not nullable.
last_round_start_timebigintTotal time, in milliseconds, taken by the clock to complete the previous round. Is not nullable.
pdw_node_idintApplies to: Azure SQL Data Warehouse, Parallel Data Warehouse

The identifier for the node that this distribution is on.

Requires VIEW SERVER STATE permission on the server.

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.

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