Marc Herbert wrote:
> Oliver Jowett <oliver@opencloud.com> writes:
>
>
>>It's not a bug. setMaxRows() is essentially a hint, there's certainly
>>no requirement that the driver will go off and add LIMIT clauses to
>>your query,
>
>
> My reading of the JDBC javadoc and my excessive "pickiness" do not
> agree with the word "hint"
>
> /**
> * Sets the limit for the maximum number of rows that any
> * <code>ResultSet</code> object can contain to the given number.
> * If the limit is exceeded, the excess
> * rows are silently dropped.
>
>
> OK nothing ever tells you that the server has to behave optimally and
> never compute anything useless. However in this case you know _for
> sure_ that additional rows will be useless.
I would assume that if the intent of the spec was "put LIMIT on the
query", they would say that.
As it stands all it does from an API point of view is change the
behaviour of the ResultSet. Whether that does anything for efficiency is
an implementation decision. The driver certainly behaves correctly
according to the API, which was my point.
There are other optimizations you can make that don't affect query
execution at all -- for example, you know you only need to store the
first N rows returned, not all of them.
-O