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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Cache a table
BTW, a good text to really understand the "touch counts" is found
here:
http://cslibrary.stanford.edu/105/LinkedListProblems.pdf
It's not oracle specific, but gives you a hint how do things work.
On 10/21/2003 05:14:28 PM, Mladen Gogala wrote:
> 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 >> >> Fat City Network Services -- 858-538-5051 http://www.fatcity.com >> San Diego, California -- Mailing list and web hosting >> services >> --------------------------------------------------------------------- >> To REMOVE yourself from this mailing list, send an E-Mail message >> to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in >> the message BODY, include a line containing: UNSUB ORACLE-L >> (or the name of mailing list you want to be removed from). You may >> also send the HELP command for other information (like subscribing).
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-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Mladen Gogala INET: mladen_at_wangtrading.com Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Tue Oct 21 2003 - 16:29:25 CDT
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