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Message Posted: Tue, 30 Dec 2003 @ 10:37:00 GMT

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Yes, it is the correct behaviour shown by identity column, the numbers that are generated have gaps(as is presented in your mailgram) which is a characteristics of the IDCOL feature. The behavior is due to the fact that it is either the AMP/PE that generates these values.

On how it works, initially the attributes you have provided are stored in one of the DBC table. Based on the kind of insert(BULK/Singleton) values are cached either in the AMP/PE caches. On receiving the first set of inserts and depending on the kind of inserts the AMPs/PEs try to fetch the next set of values from the DBC table and also rewrite the values stored in the DBC table. After fetching each vproc(AMP/PE) would try to cache a subset of values, which it would provide to the rows being inserted.

So if you were to have 4 AMPs each would cache value starting with a different value and ending with a different value depending on what it fetched from the DBC table. This thereby ensure there will not be any clash of values generated/provided by these AMPs. The similar would be the case of the PEs.

I guess now you would appreciate the non-sequential values generated by the feature.

May be this is not what the other database vendors provide as a system generated value - the 'sequence' in Oracle(I guess). There is also a reason why the feature has been developed in this manner !!!

Narayan

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