Re: Re: Proposal to fix Statement.executeBatch() - Mailing list pgsql-jdbc

Rene,

This writeup looks good.  As for your two followup questions:

1)  I agree with your opinion on the select issue.  Since selects are
the only way to call functions and functions could themselves be doing
inserts/updates, to not allow selects is a bad idea IMHO.

2)  The 8K limitation was removed from the database in 7.0 and from the
JDBC driver in 7.0.2.  Therefore I don't think we should code for the
case of a 7.2 JDBC driver needing to support a 6.5 database.

thanks,
--Barry


Rene Pijlman wrote:
> On Mon, 27 Aug 2001 22:57:13 -0700, Barry Lind wrote:
>
>>I do not know what the server does if you have autocommit enabled
>>and you issue multiple statements in one try.
>>
>
> As you know, Peter Eisentraut said on hackers that all
> statements in a semicolon-separated query string are processed
> as one single transaction. So, if in "S1;S2;S3" S2 fails, both
> S1, S2 and S3 are rolled back and in effect they have all
> failed.
>
> I think this means we can implement your proposal. I've removed
> the paragraph saying that we can't and I've added the following
> to http://lab.applinet.nl/postgresql-jdbc/#Batch
>
> -+-+-
>
> The current implementation of Statement.executeBatch() in the
> JDBC driver does not provide any performance improvement
> compared to processing statements individually. This is because
> the driver executes the statements one-by-one when
> executeBatch() is called, using one round trip per statement. We
> intend to reimplement executeBatch() in the following way.
>
> Statement.executeBatch() will send all statements in a single
> semicolon separated query string, with only one round trip to
> the backend. This will provide a performance improvement, as
> intended by the JDBC specification.
>
> The updateCounts array will be set as described below. Note that
> the JDBC spec defines the meaning of the following special
> values:
>
> -2 the statement was executed successfully but the number of
> affected rows is unknown
> -3 the statement failed to execute successfully
>
> If all statements succeed, executeBatch() returns an
> updateCounts array with a row count for each statement in the
> batch, however the value for all but the last statement will be
> -2. The value for the last statement will be a proper update
> count.
> If a statement fails, executeBatch() throws a
> BatchUpdateException containing an updateCounts array with a row
> count of -3 for each statement in the batch.
>
> Note that the behaviour will be the same when autocommit is
> enabled and when it is disabled. Even with autocommit enabled,
> the backend will commit or rollback all statements in the
> semicolon-separated query string as a unit.
>
> The new implementation of executeBatch() will cause a change in
> behaviour of the driver: the driver will no longer return update
> counts for all statements in a batch like it currently does, it
> will return -2 ("unknown") for most statements. However, this
> behaviour is allowed by the JDBC spec and applications should be
> prepared to handle it.
>
> -+-+-
>
> I see two more issues we need to decide on...
>
> 1) The JDBC spec requires Statement.executeBatch() to throw a
> BatchUpdateException if any of the statements does not return an
> update count (e.g. is a SELECT). How can we implement this? Do
> we need to parse the statements in the JDBC driver to detect
> SELECT's? It is a matter of interpretation, but it seems OK to
> me to just ignore this and return -2/-3 for SELECT's as well. In
> fact, perhaps we should allow SELECT's for function calls!?
>
> 2) The reimplementation may cause the driver to send very long
> statements to the backend. I heard something about an 8K limit.
> In what version of the backend was this limitation removed? I
> guess we should implement the new algorithm conditionally, so
> we'll only send multi-statement query strings to a backend that
> has no statement length limitation.
>
> Regards,
> René Pijlman <rene@lab.applinet.nl>
>