sp_sysmon diff between cache search miss and cache miss

[Former Member]

Hi all,

I have a question about sp_sysmon output, more precisely the figures between 'task context switch due to cache search miss' and 'cache miss' in data cache management.

Let's take an example of sp_sysmon.

The task context switch due to cache search miss shows the number below

Cache Search Misses              22.6          43.3       13582       9.7 %

This number looks high and my data cache might not be well configured but if I look at the Data Cache Management section , I have

Cache Statistics Summary (All Caches)

  -------------------------------------

                                  per sec      per xact       count  % of total

                             ------------  ------------  ----------  ----------

    Cache Search Summary

      Total Cache Hits            15436.0       29495.5     9261597      99.9 %

      Total Cache Misses             22.6          43.3       13586       0.1 %

Now the total cache misses looks fairly low and my data cache seems OK for me.

Could you explain me the difference between the 9.7% on one hand and the 0.1% on the other hand?

Thanks

Simon

[Former Member · Accepted solution]

To rephrase what Avinash said:

• Roughly 10% of your tasks dropped off the run queue since they hit a "cache miss".
• Overall you cache hit statistics is pretty good.  You will not be able to solve the 10% context switch due to cache miss by simply making the cache bigger.  You will have to dig in to see which objects are missing from the cache and if you can identify the objects that are constantly missing you may find a way to amend this (say by using a named cache)

HTH.

[Former Member]

Thanks Avinash, Andrew for your inputs.

I'll try to find out those missing objects and potentially bind them to a named cache.

Simon

[former_member89972]

Can not compare percentages like that.

First figure 9.7%  is based on "total number of context switches" so the the denominator to calculate percent is total number of context switches.

For the second figure it is based on total number of hits+misses within all data caches. So hits + misses will add up to 100% as you can see.

Avinash