Negative performance impact of index

Question

A 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.

Answer 1

djenkins99 wrote:
Is there a way to measure the impact of an index on inserts and updates? I could generate an explain plan, but I don't know how to translate the results of the explain plan into actual time (seconds less or more it takes a statement to execute). Even with my select statement, the explain plans taken before and after adding the index are definitely different, and the explain plan with the index shows it being used, although the total cost of the query with or without the index is minimally different.The "cost" of INDEX maintenance is not available as separate metric as far as I know.
It can be obtained indirectly.
1) CREATE TABLE BENCH(ID NUMBER);
2) INSERT INTO BENCH SELECT ID FROM MANY_ROWS_TABLE;
measure how long INSERT takes
SHUTDOWN IMMEDIATE
STARTUP
-- clears SGA of cached rows
3) TRUNCATE TABLE BENCH;
4) CREATE INDEX NDX_ID ON BENCH(ID);
5) INSERT INTO BENCH SELECT ID FROM MANY_ROWS_TABLE;
measure how long INSERT takes
the duration difference is cost to maintain the INDEX