Re: Estimating sizes of indexes

Jim Kunzman writes: >Informix provides very useful tools for estimating sizes of rows in >a table. Perhaps I've overlooked it, but I can find nothing about >estimating sizes for indexes. In other words, given table X with >indexes A, B, and C, how much overhead is required for each additional >row in table X? > >Can this be done easily? Is there somewhere in the documentation where >this is covered? Is there any difference in overhead for SE and Online >(unfortunately, we have to support both)? For OnLine, this is covered (in the Guide to SQL Tutorial, pg 10-16) under Estimating Index Pages. There is some difference between SE and OnLine - to keep it simple, consider SE's "page size" to be 1K (since index "nodes" are 1 page in OnLine and 1K in SE). The resulting number is really an approximation, since it is impossible to accurately predict b+tree overhead without knowing how and when the keys were inserted, exactly how many duplicates of each key (when applicable) etc., but it can get you pretty much in the ballpark. Dave -- Disclaimer: These opinions are not those of Informix Software, Inc. ************************************************************************** "I look back with some satisfaction on what an idiot I was when I was 25, but when I do that, I'm assuming I'm no longer an idiot." - Andy Rooney