In [url=https://msdn.microsoft.com/en-us/library/dn148262.aspx]this Microsoft whitepaper[/url] (and word for word in Kalen Delaney's SQL Server 2012 Internals Book, except Delaney's book doesn't state that two IOs and two context switches account for 1 tick, her book says this is 1:1), it is claimed that a plan cache entries' cost is calculated as follows:------------------------------------------------------------------------------Cost = I/O cost + context switch cost (a measure of CPU cost) + memory costThe individual parts of the cost are calculated as follows.• Two I/Os cost 1 tick, with a maximum of 19 ticks.• Two context switches cost 1 tick, with a maximum of 8 ticks.• Sixteen memory pages (128 KB) cost 1 tick, with a maximum of 4 ticks.------------------------------------------------------------------------------When I join [i]sys.dm_exec_cached_plans[/i] to [i]sys.dm_os_memory_cache_entries[/i] on [i]memory_object_address[/i] to view the cost of my plan cache entries, I can see this maps to the documented cost [i]n[/i] as 2^n for some plans, but not all; in my testing the majority deviate.I see plans with the maximum negative signed integer (-2,147,483,648) as well, is anyone aware what that may mean?Is there any further information on the discrepancies?[b]Query for Reference:[/b][code="sql"]SELECT db_name(st.dbid) [database_name] ,object_name(st.objectid, st.dbid) [OBJECT_NAME], objtype, refcounts, usecounts, cast((size_in_bytes/power(2.0,20)) as decimal(10,2)) [size_in_mb], disk_ios_count, context_switches_count, pages_kb as MemoryKB, original_cost, current_cost, case when original_cost > 0 then log(original_cost,2) else original_cost end as [lg_cost] --DOCUMENTED COST CALCULATION ,case when disk_ios_count/2 > 19 then 19 else disk_ios_count/2 end [disk_io_cost] ,case when context_switches_count/2 > 8 then 8 else context_switches_count/2 end [cpu_cost] ,case when (pages_kb/(8*16)) > 4 then 4 else (pages_kb/(8*16)) end [pages_cost] , (case when disk_ios_count/2 > 19 then 19 else disk_ios_count/2 end ) + (case when context_switches_count/2 > 8 then 8 else context_switches_count/2 end) + (case when (pages_kb/(8*16)) > 4 then 4 else (pages_kb/(8*16)) end) [documented_cost_calculation] FROM sys.dm_exec_cached_plans pCROSS APPLY sys.dm_exec_sql_text(plan_handle) stJOIN sys.dm_os_memory_cache_entries eON p.memory_object_address = e.memory_object_addressWHERE cacheobjtype = 'Compiled Plan'AND type in ('CACHESTORE_SQLCP', 'CACHESTORE_OBJCP')and objtype = 'proc'order by original_cost[/code]Note: changing the 2:1 ratio to 1:1 results in a similar number of misses
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