Re: 'Physical Reads' in statspack doesn't match I/O waits

<mccmx_at_hotmail.com> wrote in message
news:1145545488.647071.262530_at_v46g2000cwv.googlegroups.com...
> 9.2.0.6 on Windows
>
> I am getting unexpected results from a statsoack output:
>
> The 'physical reads' value in the "Instance Activity Stats" section is
> as follows:
>
> ....
> physical reads 1,075,088
> ....
>
> but this does not match the number of I/O waits in the "Top 5 Timed
> Events" section:
>
> Top 5 Timed Events
>
> db file sequential read 234,386
> db file scattered read 129,911
> ....
>
> Nor does it match the total number of reads in the "Tablespace I/O
> Stats" section:
>
> 364,373
>
> So the value in the "Instance Activity Stats" appears to be the
> incorrect value. However the SQL section seems to base its '%Total'
> value for a statement on this value rather than the other value.
>
> Does the 'physical reads' stat include other I/O that is not included
> in the other 2 sections..?!?
>
> Thanks in advance
>
> Matt
>

System stats

    "physical reads" is the number of _blocks_ read

Tablespace IO

    "reads" is the number of read requests.

            multiply per tablespace by "Av blks/read"
            to get to the physical reads in system stats

db file scattered reads = number of multiblock requests db file sequential reads = number of single block read requests

    These two sum (very nearly) to the reads in tablespace I/O

-- 
Regards

Jonathan Lewis
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