RE: Sequence Skipping
- From: "Lange, Kevin G" <kevin.lange@xxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 13 Jun 2012 15:31:31 -0500
If the sequence is used to set the key in lookup tables that have a max
size on said field, then nocache would be appropriate. Otherwise,
dropping x amount of sequence values could blow out the max that is set
prematurely.
Basically, any infrequantly used system generated key field is a
candidate for nocache.
Of course, that's only my opinion.
Kevin
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Tim Gorman
Sent: Wednesday, June 13, 2012 3:26 PM
To: Scott.Graves@xxxxxxxxx; oracle-l@xxxxxxxxxxxxx
Subject: Re: Sequence Skipping
There is absolutely no evidence that the sequence is being "flushed from
the SGA", but rather more likely that the WHEN NOT MATCHED condition of
the MERGE statement (i.e. when the sequence NEXTVAL is referenced) is
possibly 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 more pain than the
"problem".
However, *temporarily* setting the sequence to NOCACHE might be a useful
diagnostic technique, as a SQL trace of the MERGE statement would then
clearly indicate whether the sequence is being accessed inappropriately
during WHEN MATCHED, as the recursive UPDATE SEQ$ statement should be
visible and countable.
But setting a sequence to NOCACHE is almost always due to a typo during
CREATE/ALTER SEQUENCE or a misunderstanding of when to use/when not to
use sequences. The only appropriate use of NOCACHE is diagnostic, such
as described just above. I'd be curious to know if anyone has any other
valid use of NOCACHE or even under-caching a sequence?
-----Original Message-----
From: Scott Graves [mailto:Scott.Graves@xxxxxxxxx]
Sent: Wednesday, June 13, 2012 01:51 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: Sequence Skipping
When the sequence is flushed from the SGA, the unused numbers in the
cache are burnt. Set your sequences to nocache and that behavior goes
away.-----Original Message-----From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Kenneth NaimSent:
Wednesday, June 13, 2012 2:32 PMTo: oracle-l@xxxxxxxxxxxxxxxxxxxx:
Sequence SkippingI use the following two merge statements to load data
into a dimension table nightly. Every night the process runs the
sequence (seq_procedure_key) gets incremented by approximetly 57,000
values even though only 4-37 rows are added. There are about 57,000 in
the procedures table, Millions in the medical_bill_detail tables and 17k
in the cpt table. It seems one of the two merge statements is wasting 1
sequence value for every row that does not get inserted. I've tried
searching metalink for bugs and so far have come up empty. I am
experiencing this in 10.2.0.3 prod environment and an 11.2.0.3 test
environment. If this is ex pected behavior, any known workarounds. I
don't mind losing some values but 57k per day is too many. The load
failed 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 sequence
is 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 set
a.procedure_name=b.cpt_descr where
nvl(procedure_name,'~')<>nvl(b.cpt_descr,'~') and cpt_descr is not null
when 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 distinct
replace(cpt_code,' ') cpt_code, null cpt_de scr from
wcis_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_procedure_key.nextval, b.cpt_code,
b.cpt_descr);Thanks,Ken
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