How is the buf_cachehit_ratio checkpoint calculation done by sqlserver probe

Document ID:  TEC1417647
Last Modified Date:  07/17/2017
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How is buf_cachehit_ratio checkpoint calculation done by sqlserver probe 

sql_server 5.10 sql_server 5.2x

Query executed for buf_cachehit_ratio checkpoint:

select convert(dec(12,0),a.cntr_value) as page_lookups, convert(dec(12,0),b.cntr_value) as page_reads, convert(dec(12,0),c.cntr_value) as page_writes from master.dbo.sysperfinfo a, master.dbo.sysperfinfo b, master.dbo.sysperfinfo c where a.counter_name = 'Page lookups/sec' and b.counter_name = 'Page reads/sec' and c.counter_name = 'Page writes/sec'


Variables :

lookups = Delta of current & last sample value of page_lookups column value

reads = Delta of current & last sample value of page_reads column value

writes = Delta of current & last sample value of page_writes column value


Formula :

if (lookups > 0) {


                hit = ((lookups - reads - writes) / lookups) *100;


else {

                hit = 100;



This 'hit' value is sent as QOS and gets compared with the threshold

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