Re: dictionary misses VS Read consistency

Now I understand why I can't get my hit-rate up because of what you say. On one of my (?) databases WITHOUT synonyms I have a Dictionary cache hit rate of 99,94%
One another WITH synonyms ! can't seem to get it over 97%. Not a problem, but still....

Of course the Library-cache is important too, but if your Dictionary cache is low, it will be a problem to get the Library-cache up. (99.7% in the first case).
My problem is obviously not in this caches, but merely in my read-consistency, it's only 35.5% :-(
The nature of the first database is, that ALL records are addressed regularly, and I can't keep them all in memory (The computer can't either)

The main idea is, not to overvalue the Dictionary- and Library caches. A larger SGA will do the job. A low read-consistency like mine is killing your performance!
Spreading the data over 40 disks with 8 controllers is just one of the 'workarounds' we applied. Next step is to introduce Veritas filesystem with the Filesystem- to Raw device add-on (Don't ask me how it works, we have a Sun-specialist for these matters)

Eric Lansu
www.sonera.com

P.S. The ", after the second line in the script is missing, but no-one overlooked this of course...

• Original Message ----- From: "Steve Adams" <steve.adams_at_ixora.com.au> To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Tuesday, 23 May 2000 00:58 Subject: RE: dictionary misses

> Hi Ruth,
>
> It depends on whether you use synonyms.
> If you don't use ANY synonyms, then hit rates of 99% can be seen.
> If you do, then the hit rates can be very low.
>
> Note also that it is the library cache hit rate that you should focus on,
not the dictionary cache one.
> The dictionary cache is used merely to load the library cache if you get a
miss there.
> (OK, that's an over-statement because it ignores the locking
functionality, but you get the idea).
>
> Regards,
> Steve Adams
> http://www.ixora.com.au/
> http://www.oreilly.com/catalog/orinternals/
> http://www.christianity.net.au/
>
>
> -----Original Message-----
> From: Ruth Gramolini [SMTP:rgramolini_at_tax.state.vt.us]
> Sent: Tuesday, May 23, 2000 12:46 AM
> To: Multiple recipients of list ORACLE-L
> Subject: dictionary misses
>
> Hi all,
>
> Can anyone tell me the acceptable range for dictionary misses when using
> this script?
> SELECT SUM(getmisses) "Dict Misses",
> SUM(gets) "Requests
> 100-(100*(SUM(getmisses)/SUM(gets))) "Hit%",
> 100*(SUM(getmisses)/SUM(gets)) "Miss%"
> FROM v$rowcache;
>
> I think I remember it needs be less than 5% but I can't remember.
>
> Thanks in advance,
> Ruth B. Gramolini
> ORACLE DBA
> VT Dept. of Taxes
Received on Tue May 23 2000 - 00:57:16 CDT