Allow to set arbitrary Integer values to FetchSize

[michele-mancioppi]

Rework the fetchSize parameter to allow the specification of negative integers
like Integer.MIN_VALUE, which is needed in some typoes of queries.

See https://dev.mysql.com/doc/connector-j/5.1/en/connector-j-reference-implementation-notes.html

Closes #78

[davidmoten]

Thanks for the PR.

Why change fetchSize from int to Integer? Does fetchSize of 0 have meaning?

I also haven't understood what is the difference between setting fetchSize to Integer.MIN_VALUE and setting fetchSize to 1. What do you think is the difference?

[davidmoten]

I just read

https://stackoverflow.com/questions/26046234/is-there-a-mysql-jdbc-that-will-respect-fetchsize/36986532#36986532

If you enable the MySQL JDBC option useCursorFetch, fetchSize will indeed be respected by the driver.

However, there is one disadvantage to this approach: It will use server-side cursors, which in MySQL are implemented using temporary tables. This will mean that results will not arrive until the query has been completed on the server, and that additional memory will be used server-side.

If you just want to use result streaming and don't care about the exact fetch size, the overhead of setFetchSize(Integer.MIN_VALUE) is not as bad as the docs might imply. It actually just disables client-side caching of the entire response and gives you responses as they arrive; there is no round-trip per row required.

On this basis I would continue using 0 for not set, allow Integer.MIN_VALUE as a valid fetchSize and not allow any other negative value. What do you think?

[davidmoten]

for mysql it looks like fetchSize=Integer.MIN_VALUE enables backpressure at the TCP socket:

With MIN_VALUE, MySQL seems to rely on the underlying TCP socket's flow control. As long as the receive window is reasonably sized (and all modern OSes do that by default), you should never have to wait for more data except if your read is bandwidth-limited in the first place

[litalk]

Great! if it could be merged soon it would be very appreciated.

[michele-mancioppi]

It seems that drivers take some latitude with setFetchSize and the values set in there. MySQL is an example, but I dug a bit in proprietary databases on my side and apparently we do some "creative" interpretations there too :-) So I am no longer very optimistic about using 0 as default.

If we were on Java 8, I'd have used an Optional, but to keep the PR simple I just went with the boxed version of int to have the "null as not set" semantic.

[michele-mancioppi]

In other words, if we go with "0 is default, Integer.MIN_VALUE is the only negative int accepted" we risk having another issue about this the next time a quirky driver comes along.

[davidmoten]

In other words, if we go with "0 is default, Integer.MIN_VALUE is the only negative int accepted" we risk having another issue about this the next time a quirky driver comes along.

I'm happy with your argument. I'll merge and release.

[davidmoten]

released to Maven Central 0.7.7