Hi Tamar,

I have been reading this whole thread but didn't participate. However, I kept on asking myself what happens if the tag is INDEX ON .NOT.DELETED() ? Is it the same situation that happens with Rushmore ? I think so since the index is still divided in two groups right ?

Thanks!
Sylvain

>>Walter,
>>
>> I think the key is what is the highest % of deleted records that could be in your table. I assume with SET DELETED ON that VFP would have to omit ANY deleted records from a result query without optimization. This may not be a huge issue with a few dozen records in a 5000 record table. But in a 20 million record table with tens of thousands of deleted records then not having the DELETED tag could mean you are losing lots of optimization. If 50% or more of the records in the file could be deleted it would be hard to argue against including an index tag to improve performance.
>
>However, the flip side has to do with the way Rushmore works. When there's a matching index tag, Rushmore brings the portion of the index for records matching the specified condition into memory. When you have a key like DELETED(), which doesn't differentiate very much (that is, it divides the data only into two groups, and usually one group is much larger than the other), the size of that portion of the index file may be so large and take so long to transfer that manually checking the records that match all the other conditions may be faster.
>
>That is, in many cases, other conditions rule out a lot of records, so by the time you have to check whether a record is actually deleted, the number of records to read is quite small. When Rushmore uses the tag, it has to read the entire portion of the index file that corresponds to the appropriate value of the key. In your example, Rushmore will read in half of the portion of the index file that holds the DELETED() information. If other conditions in the query cut down the number of records that could possibly be in the result set, the total size of the remaining records may be much smaller than the size of that portion of the index.
>
>Tamar