Negative performance impact of index
17132Apr 4 2012 — edited Apr 4 2012A SELECT statement I've written references an otherwise unused VARCHAR2 column in a table that defaults to NULL, and which is set by another statement for some (not all) rows to a three-character string (like 'XYZ'). The query takes 2.5 hours to complete, but with an index added on the column, finishes in 2 to 3 minutes. I'm perfectly satisfied with this solution, but my extremely cautious colleagues (one in particular) are concerned that adding an index will negatively impact the performance of other INSERT or UPDATE statements that reference the table but not the column. I think they're being wildly overcautious, that an index on a column that can contain only 2 values will have minimal impact on other DML statements, if any. Am I right? Is there a reference I could consult to settle disputes like this?
Any opinions would be gratefully accepted.