Re: Sequence Skipping
Date: Wed, 13 Jun 2012 20:38:02 +0000
Message-ID: <W1970622993207721339619882_at_webmail11>
I don't understand the implied relationship between the sequence value returned and caching. Could you explain? And why would it be useful to use NOCACHE (except for diagnostics), even for infrequently-used sequences? What would be the advantage?
-----Original Message-----
From: Lange, Kevin G [mailto:kevin.lange_at_ppoone.com]
Sent: Wednesday, June 13, 2012 02:31 PM
To: oracle-l_at_freelists.org
Subject: RE: Sequence Skipping
If the sequence is used to set the key in lookup tables that have a maxsize on said field, then nocache would be appropriate. Otherwise,dropping x amount of sequence values could blow out the max that is setprematurely.Basically, any infrequantly used system generated key field is acandidate for nocache.Of course, that's only my opinion.Kevin-----Original Message-----From: oracle-l-bounce_at_freelists.org[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Tim GormanSent: Wednesday, June 13, 2012 3:26 PMTo: Scott.Graves_at_nisc.coop; oracle-l_at_freelists.orgSubject: Re: Sequence SkippingThere is absolutely no evidence that the sequence is being "flushed fromthe SGA", but rather more likely that the WHEN NOT MATCHED condition ofthe MERGE statement (i.e. when the sequence NEXTVAL is referenced) ispossibly being accessed unnecessarly during the WHEN MATCHED condition.Setting NOCACHE on a heavily-accessed sequence as a perceived "solution"is the classic situation of the "cure" causing mo re pain than the"problem".However, *temporarily* setting the sequence to NOCACHE might be a usefuldiagnostic technique, as a SQL trace of the MERGE statement would thenclearly indicate whether the sequence is being accessed inappropriatelyduring WHEN MATCHED, as the recursive UPDATE SEQ$ statement should bevisible and countable.But setting a sequence to NOCACHE is almost always due to a typo duringCREATE/ALTER SEQUENCE or a misunderstanding of when to use/when not touse sequences. The only appropriate use of NOCACHE is diagnostic, suchas described just above. I'd be curious to know if anyone has any othervalid use of NOCACHE or even under-caching a sequence?-----Original Message-----From: Scott Graves [mailto:Scott.Graves_at_nisc.coop]Sent: Wednesday, June 13, 2012 01:51 PMTo: oracle-l_at_freelists.orgSubject: RE: Sequence SkippingWhen the sequence is flushed from the SGA, the unused numbers in thecache are burnt. Set your sequences to nocache and that behavior goesaway.-----Origi nal Message-----From: oracle-l-bounce_at_freelists.org[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Kenneth NaimSent:Wednesday, June 13, 2012 2:32 PMTo: oracle-l_at_freelists.orgSubject:Sequence SkippingI use the following two merge statements to load datainto a dimension table nightly. Every night the process runs thesequence (seq_procedure_key) gets incremented by approximetly 57,000values even though only 4-37 rows are added. There are about 57,000 inthe procedures table, Millions in the medical_bill_detail tables and 17kin the cpt table. It seems one of the two merge statements is wasting 1sequence value for every row that does not get inserted. I've triedsearching metalink for bugs and so far have come up empty. I amexperiencing this in 10.2.0.3 prod environment and an 11.2.0.3 testenvironment. If this is ex pected behavior, any known workarounds. Idon't mind losing some values but 57k per day is too many. The loadfailed as the column related to the sequence was defined as number(8)and the sequence was into the 9th digit. BTW the cache on the sequenceis 50.merge into procedures a using (select nvl(replace(cpt_code,''),'None') cpt_code, cpt_descr from cpt where cpt_code is not null) b on(a.cpt_code=b.cpt_code) when matched then update seta.procedure_name=b.cpt_descr wherenvl(procedure_name,'~')<>nvl(b.cpt_descr,'~') and cpt_descr is not nullwhen not matched then insert (procedure_key, cpt_code, procedure_name)values (seq_procedure_key.nextval, b.cpt_code, b.cpt_descr);v_number_of_records:=sql%rowcount; pkg_etl.p_end_process(v_process_id,v_number_of_records, null, false); v_process_type_id: 9;pkg_etl.p_start_process(v_process_type_id, load_id_in, null, null, null,v_process_id); merge into procedures a using (select distinctreplace(cpt_code,' ') cpt_code, null cpt_de scr fromwcis_dba.medical_bill_detail where cpt_code is not null) b on(a.cpt_code=b.cpt_code) when not matched then insert (procedure_key,cpt_code, procedure_name) values (seq_pro cedure_key.nextval, b.cpt_code,b.cpt_descr);Thanks,Ken--http://www.freelists.org/webpage/oracle-lThis e-mail, including attachments, may include confidential and/orproprietary information, and may be used only by the person or entityto which it is addressed. If the reader of this e-mail is not the intendedrecipient or his or her authorized agent, the reader is hereby notifiedthat any dissemination, distribution or copying of this e-mail isprohibited. If you have received this e-mail in error, please notify thesender by replying to this message and delete this e-mail immediately.--http://www.freelists.org/webpage/oracle-l
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Received on Wed Jun 13 2012 - 15:38:02 CDT