Обсуждение: Adding support for batches that return generated keys

Hi all

I've implemented support for batches that return generated keys.

https://github.com/pgjdbc/pgjdbc/pull/204

and I'm looking for feedback before I merge this into master.


Currently the driver internally executes these one-by-one, which is
pretty horrible if there's a big round-trip involved.

Details in Github issue #195:

https://github.com/pgjdbc/pgjdbc/issues/195



With this change PgJDBC now executes batches that return generated keys
in internal sub-batches separated by periodic Sync, flush, and input
consume pauses, just, like it does for batches that don't return keys.

This is safe (or almost as safe as it ever was given github #194)
because we force a Describe, then estimate the result row size and
adjust the batch size accordingly.

This approach does increase the deadlock risk if a batch executes
statements where each statement returns many generated keys (e.g. a big
multi-entry VALUES clause or an INSERT INTO ... SELECT ...), as it
assumes each execution will only return one generated key. That's a
fairly reasonable assumption, given that the lack of intra-statement
ordering guarantees means you can't reliably associate generated keys to
the values that generated them unless you run one statement per
generated result. I don't expect this to be an issue in practice. In any
case, anyone who's doing this is likely to be doing so as an attempt to
work around the very limitation this commit fixes.
--
 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Hello Craig,

On 10/10/2014 11:02, Craig Ringer wrote:
> Hi all
>
> I've implemented support for batches that return generated keys.
>
> https://github.com/pgjdbc/pgjdbc/pull/204
>
> and I'm looking for feedback before I merge this into master.

I spent some time in looking your patch. Since I am just beginning
studying how pgjdbc works, I cannot speak about correctness of the code,
but I still have two questions:

First one is about the java version you are using. It seems to me that
the driver should be compileable in java 1.4, i.e., on a java version
that doesn't  use int and Integer in a mixed way. At the end of
getMaxResultRowSize() in org/postgresql/core/v3/SimpleQuery.java you
assign an int value to an Integer variable. Is this correct?
On the very same method, on the first lines, you extract the intValue()
from the Integer variable.

Second, in method flushIfDeadlockRisk(...) in file
org/postgresql/core/v3/QueryExecutorImpl.java, about line 1169, you use
the word "uresults". Is this a typo or a data structure used by pgjdbc?

Bye,
Giuseppe