"Hit a table that keeps a counter" will not scale (will not perform at high concurrency). It will cause you no end of "buffer busy waits" waits, "latch free" waits for a cache buffers chains latch (even if db_block_buffers, _db_block_hash_buckets, and _db_block_hash_latches could be set to infinity), lots of unnecessary CPU service consumption due to the spinning (especially if you try to tinker with _spin_count), and possibly a wide range of side effects including "write complete waits" waits and others.
Cary Millsap Hotsos Enterprises, Ltd. http://www.hotsos.com Upcoming events: - Performance Diagnosis 101: 11/19 Sydney - SQL Optimization 101: 12/8-12 Dallas - Hotsos Symposium 2004: March 7-10 Dallas - Visit www.hotsos.com for schedule details... -----Original Message----- Hemant K Chitale Sent: Wednesday, November 05, 2003 8:25 AM To: Multiple recipients of list ORACLE-L My comments [probably off-the-cuff without spending much time thinking the issues through .....?] 1. Hit a table that keeps a counter. Used to be a mechanism in the Oracle5 days [If I remember correctly, Sequences came in Oracle6]. Issues were with locking the single record used as the generator or scanning for the max(value) of the key. Not quite sure I understand how you encountered concurrency issues, though. 2. Stored sequences. Although I prefer not to use a Sequence as a PK in itself [preferring natural column/s which are Unique keys, with the NOT NULL, of course], I have used a Sequence in an Advanced Replication implementation that had no Primary Key and I needed a PK for Conflict Resolution [this was years ago and, if you ask me, I can't remember all the details] 3. SYS_GUID SYS_GUID I've never used. It doesn't generate a NUMBER value so it is not really similar to a Sequence. Can user's key in a SYS_GUID-generated value ? Is it really "human readable" or "recallable" as a plain NUMBER, Security Security Number, ZIP Code ?? 4. Similar to SYS_GUID .. You hit on a fortuitous combination of columns. Hemant At 05:19 AM 05-11-03 -0800, you wrote: >The recent article that mentioned sequences got me to >thinking. I might pitch a more detailed article on sequences >to Builder.com. But a more interesting article might be one >that explored various ways to automatically generate primary >keys. So, in the name of research, let me throw out the >following questions: > >What mechanisms have you used to generate primary keys? >Which ones worked well, and why? Which mechanisms worked >poorly? > >I've run up against the following approaches: > >* Hit a table that keeps a counter. This is the "roll your >own sequence method". The one time I recall encountering >this approach, I helped convert it over to using stored >sequences. This was because of concurrency problems: with >careful timing, two users could end up with the same ID >number for different records. Is there ever a case when this >roll-your-own approach makes sense, and is workable? > >* Stored sequences. I worked on one app that used a separate >sequence for each automatically generated primary key. I >worked on another app, a smaller one, that used the same >sequence for more than one table. The only issue that I >recall is that sometimes numbers would be skipped. But end >users really didn't care, or even notice. > >* The SYS_GUID approach. I've never used SYS_GUID as a >primary key generator. I wonder, was that Oracle's >motivation for creating the function? Has anyone used it for >primary keys in a production app? What's the real reason >Oracle created this function? > >* Similar to SYS_GUID, I once worked on an obituary-tracking >application that built up a primary key from, as best I can >recall now: date of death, part of surname, part of first >name, and a sequence number used only to resolve collisions, >of which there were few. The approached worked well, >actually, because whatever fields we munged together to >generate a primary key gave us a unique key the vast >majority of the time. > >The SYS_GUID approach is interesting, but if you need an ID >number that users will see, and that users might type in >themselves (e.g. social security number), is SYS_GUID really >all that viable? > >Best regards, > >Jonathan Gennick --- Brighten the corner where you are >http://Gennick.com * 906.387.1698 * mailto:[EMAIL PROTECTED] > >Join the Oracle-article list and receive one >article on Oracle technologies per month by >email. To join, visit >http://four.pairlist.net/mailman/listinfo/oracle-article, >or send email to [EMAIL PROTECTED] and >include the word "subscribe" in either the subject or body. > >-- >Please see the official ORACLE-L FAQ: http://www.orafaq.net >-- >Author: Jonathan Gennick > 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). Hemant K Chitale Oracle 9i Database Administrator Certified Professional My personal web site is : http://hkchital.tripod.com -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Hemant K Chitale 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: Cary Millsap 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).
