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: [EMAIL PROTECTED] > > 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: [EMAIL PROTECTED] (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). Mladen Gogala Oracle DBA Note: This message is for the named person's use only. It may contain confidential, proprietary or legally privileged information. No confidentiality or privilege is waived or lost by any mistransmission. If you receive this message in error, please immediately delete it and all copies of it from your system, destroy any hard copies of it and notify the sender. You must not, directly or indirectly, use, disclose, distribute, print, or copy any part of this message if you are not the intended recipient. Wang Trading LLC and any of its subsidiaries each reserve the right to monitor all e-mail communications through its networks. Any views expressed in this message are those of the individual sender, except where the message states otherwise and the sender is authorized to state them to be the views of any such entity. -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Mladen Gogala INET: [EMAIL PROTECTED] 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: [EMAIL PROTECTED] (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). -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Pete Sharman INET: [EMAIL PROTECTED] 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: [EMAIL PROTECTED] (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).
