On the grounds that it's not abnormal if you think of the table as "polls" and not "polled data".

Which answer is "right" depends on what sort of management queries you see yourself running in the future. If you're going to be asking questions like "what's our timeout-to-success ratio?" you might want the flag. If you want faster summaries of only valid data, you might want the separate table. How fast is the poll compared to the overhead of maintaining parallel updating tables?

> I don't see how ratio is faster with single table
> - it's simple "select count() from" versus
> "select count() from ... where ...".

The "where" is another decision that needs to be made. Depends on the DB if that's faster or not for your dataset.

> Also, I thought that updating 2 smaller tables
> is faster than updating 1 large one.

Again, depends on the size of the tables and the DB. I'm not enough of an Oracle expert to answer that for your dataset. I would have thought opening and updating a single row would be faster than 2 any day...but I'm not a low-level DB expert. I'd test each one and see which is faster.

> As to "polls" and not "polled data"...
> Could you elaborate on that? Not sure I understand.

I'm just saying that often an object seems redundant only because of the label we put on it. If you look at your dataset as a list of "successful poll values", then the timeouts look out of place. But if you look at it as a list of "poll results (successful or not)", then the timeouts attain equal "status" with the other data. If you were going to normalize this table the "idealized" way, you'd have a master index of timestamps in one, values in a second, and timeouts in a third. That's true normalization: sharing what's similar and pulling out what's different. Yuck. Two tables is, to me, just as unappealing as three when you're talking about one bit of data, unless you see some point in the future where you'd add additional data regarding the duration or cause of the timeout.

The only query that is faster on single table, IMHO, is the one that has to merge the tables. Actually, I wonder.. How the hell do I write a query that merges them, while retaining, for each record, the origin of it? IOW, how do I get from 2 tables to one with a flag? I guess my lack of SQL experience is showing.

Use a UNION query. That will get ugly for the same reasons it's ugly using two tables instead of three.

MSAccess example (hoping it's standard):
SELECT Timestamp, Name, Value, False AS IsTimeout FROM Polls
UNION
SELECT Timestamp, Null AS Name, Null AS Value, True AS Timeout FROM Timeouts