Re: Q: is DS 7.x using index?

>Query looks like: > > > SELECT * from table WHERE fld > N> > fld is UNIQUE indexed. > > Pls, help, because performance is dead slow. The use of the index is dependent upon the "selectivity" of that index. Since the query is an inequality, it is very possible that the index would not be used because a scan would be actually quicker. Let me explain. Supposed that it appears that the filter would be selecting in excess of 70% of the total number of rows. If the query were to follow the index, it is very possible that the index scan would be making multiple selects on the same page. This would mean that the same page would be "hit" multiple times during the query. In such a case, it would really make more sense to sequentially scan the table, even though we might be reading pages that contained no selected rows. However, this cost would be more than offset by the fact that each page would only be selected once. The only way to really know if the index is being used is to check the output from "set explain on". It is possible that a less than optimal query plan is being used because the nature of the data has significantly changed since the last "update statistics" was run. If it appears that there there are performance is not what is desired, it might be worth it to contact customer service and open a case for the problem. Madison Pruet