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Re: request for a feature -- LIMIT_ROWS_EXAMINED
A warning would be excellent. An error would be a problem. Returning
OK is probably not the best result when the examined limit is reached.
On Wed, Dec 21, 2011 at 7:17 AM, Timour Katchaounov
>>>>>>> "MARK" == MARK CALLAGHAN<mdcallag@xxxxxxxxx> writes:
>> MARK> I want a variant of the LIMIT clause that limits the number of rows
>> MARK> examined during SELECT processing. This should return OK when the
>> MARK> limit is reached -- something like NESTED_LOOP_QUERY_LIMIT. While
>> MARK> LIMIT can be LIMIT x and LIMIT x,y. This only supports one argument
>> MARK> LIMIT_ROWS_EXAMINED x. Are you interested in implementing this
>> MARK> for me? We will sponsor the work. The purpose of the feature is to
>> MARK> prevent queries from taking too long when there isn't a great index
>> MARK> and many rows might be filtered.
>> I am a bit afraid of returning 'ok'. Would it not be better to return
>> an error?
>> Another option would be to generate a warning so that the application
>> can know that they didn't get all rows.
> This is what I would prefer to do:
> - process the new LIMIT_ROWS_EXAMINED clause in the same way as LIMIT,
> just with a different condition to end query execution,
> - in addition produce a warning that not all rows were returned.
> Mark, does the above suit you? If you don't want to check for
> warnings, you can skip them, however users will have the option
> to detect that not all rows were returned.
>> We can do this and it should be relatively easy to do.
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