RE: Cache a table

I think you have mentioned that once or twice. :)

Pete
"Controlling developers is like herding cats." Kevin Loney, Oracle DBA Handbook
"Oh no, it's not. It's much harder than that!" Bruce Pihlamae, long-term Oracle DBA  

-----Original Message-----
Mladen Gogala
Sent: Wednesday, October 22, 2003 8:40 AM To: Multiple recipients of list ORACLE-L

Good idea. I located the meaning of TIM column (time to "age" buffer). BTW, did I tell you that I like your signature?

On 10/21/2003 05:39:25 PM, Pete Sharman wrote:
> Have a look at Steve Adam's web site. He probably knows more about
> it
> than
> just about anyone else I know (as usual!)
>
> Pete
> "Controlling developers is like herding cats."
> Kevin Loney, Oracle DBA Handbook
> "Oh no, it's not. It's much harder than that!"
> Bruce Pihlamae, long-term Oracle DBA
>
>
>
> -----Original Message-----
> Mladen Gogala
> Sent: Wednesday, October 22, 2003 7:14 AM
> To: Multiple recipients of list ORACLE-L
>
>
> Did anyone try to benchmark the touch count based algorithm against
> the old LRU list? LRU list had advantage of being intuitive, while
> touch
> count
> algorithm is depending on many parameters for which I don't exactly
> understand the impact. LRU list parameters were
> essentially defining the desired length of the free buffers list,
> while the
> touch count parameters are all undocumented and are
> signifying the size of touch pool, the interval in which block has to
>
> be touched if the touch count is to increase, the required touch
> count
>
> to be moved to the hot pool and alike. Is it more efficient then the
> previous easy and understandable LRU lists or not? Touch counts are
> visible as TCH in X$BH. I still have no clue what "TIM" is.
>
> On 10/21/2003 04:39:33 PM, Wolfgang Breitling wrote:
> > Before Oracle 8 and the new touch count algorithm the cache
> attribute
> > made sense. If a small, frequently used table was read by a full
> > scan, it would have been put at the end of the LRU chain eligible
> to
>
> > be aged out immediately, quite possibly by itself if it consisted
> of
>
> > more than ~ db_file_multiblock_read_count blocks, i.e. the 2nd or
> 3rd
> > full scan read would already override the previously read blocks.
> > Marking the table as CACHEd prevented that.
> >
> > At 01:09 PM 10/21/2003, you wrote:
> >> I always wondered why Oracle thought this was a useful table
> >> attribute.
> >>
> >> My gut feeling is that it is an extra that does little.
> >>
> >> For example, say we want to keep a code table in memory because it
> >> is constantly being hit for column verifiction. By definition, if
> >> a table is
> >> constantly being queried, it's segments will be in memory because
> >> they never
> >> age out. That sounds like cacheing to me.
> >>
> >> And then I remember a specific piece of Oracle documentation
> saying
> >> that,
> >> even though we may mark a table to be "cached", it *still* may be
> >> aged out if memory is needed for other data blocks.
> >>
> >> Like I said, sounds a little like "here you have it, and here you
> >> don't".
> >>
> >> I'm sure that my impression is wrong and someone will correct me.
>
> >> But I
> >> doubt I will use the "CACHE" option anytime soon.
> >>
> >> Tom Mercadante
> >> Oracle Certified Professional
> >
> > Wolfgang Breitling
> > Oracle7, 8, 8i, 9i OCP DBA
> > Centrex Consulting Corporation
> > http://www.centrexcc.com
> >
> >--
> > Please see the official ORACLE-L FAQ: http://www.orafaq.net
> >--
> > Author: Wolfgang Breitling
> > INET: breitliw_at_centrexcc.com
> >
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> Mladen Gogala
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>
>
>
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Mladen Gogala
Oracle DBA

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  INET: mladen_at_wangtrading.com

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