Re: The same prepared query yield "-1" the first six times and then "-1.0"

[Dave Cramer <davecramer@postgres.rocks>]

On Tue, 22 Aug 2023 at 01:54, Edoardo Panfili <edoardopa@xxxxxxxxx> wrote:

Il giorno 21 ago 2023, alle ore 21:37, Dave Cramer <davecramer@postgres.rocks> ha scritto:

On Mon, 21 Aug 2023 at 14:42, Edoardo Panfili <edoardopa@xxxxxxxxx> wrote:

> Il giorno 21 ago 2023, alle ore 20:13, Peter J. Holzer <hjp-pgsql@xxxxxx> ha scritto:
>
> On 2023-08-21 17:27:20 +0200, Edoardo Panfili wrote:
>> The attended result was a sequence of ten equal values but this is the actual result:
>> p: -1
>> p: -1
>> p: -1
>> p: -1
>> p: -1
>> p: -1.0
>> p: -1.0
>> p: -1.0
>> p: -1.0
>> p: -1.0
> [...]
>> 2023-08-21 11:51:50.633 CEST [1511] user@testdb LOG: execute <unnamed>: SET extra_float_digits = 3
>> 2023-08-21 11:51:50.634 CEST [1511] user@testdb LOG: execute <unnamed>: SET application_name = 'PostgreSQL JDBC Driver'
>> 2023-08-21 11:51:50.644 CEST [1511] user@testdb LOG: execute <unnamed>: SELECT dim1 FROM number WHERE name='first'
>> 2023-08-21 11:51:50.648 CEST [1511] user@testdb LOG: execute <unnamed>: SELECT dim1 FROM number WHERE name='first'
>> 2023-08-21 11:51:50.649 CEST [1511] user@testdb LOG: execute <unnamed>: SELECT dim1 FROM number WHERE name='first'
>> 2023-08-21 11:51:50.650 CEST [1511] user@testdb LOG: execute <unnamed>: SELECT dim1 FROM number WHERE name='first'
>> 2023-08-21 11:51:50.651 CEST [1511] user@testdb LOG: execute S_1: SELECT dim1 FROM number WHERE name='first'
>> 2023-08-21 11:51:50.651 CEST [1511] user@testdb LOG: execute S_1: SELECT dim1 FROM number WHERE name='first'
>> 2023-08-21 11:51:50.653 CEST [1511] user@testdb LOG: execute S_1: SELECT dim1 FROM number WHERE name='first'
>> 2023-08-21 11:51:50.653 CEST [1511] user@testdb LOG: execute S_1: SELECT dim1 FROM number WHERE name='first'
>> 2023-08-21 11:51:50.654 CEST [1511] user@testdb LOG: execute S_1: SELECT dim1 FROM number WHERE name='first'
>> 2023-08-21 11:51:50.656 CEST [1511] user@testdb LOG: execute S_1: SELECT dim1 FROM number WHERE name=‘first'
>
> Are these outputs from the same run?
Yes

>
> I notice that the output from the program switches after 5 queries from
> "-1" to "-1-0", but the logged query name switches after 4 queries from
> "<unnamed>" to "S_1”.

You’re right.  It seem a JDBC side problem. I am doing some tests using suggestions from pgsql-jdbc list.

What sounds strange to me is that switching from “mode_X” to  “mode_Y” I obtain different representation of the same value,

I know the value is semantically the same.. but… in some way I like to see.. "a perfect postgresql env” (as it absolutely is)

Edoardo

I have confirmed that this behaviour is by design either by postgres or the driver. When postgres provides us the data using text mode we see -1 

(psql)

select * from number ;

 name  | dim1

-------+------

 first |   -1 

This is the way the data is presented by the text output function.

And I expected to obtain the same from the JDBC connection 

In binary mode we see -1.0. This is an artifact of the binary output function.

If ResultSet.getDouble is used the data is the same ... -1 for both text and binary

Using getString we see the problem.

So you have a few options to stop this: Set prepareThreshold to 0 and the driver will not switch to named statements or binary,

Properties props = new Properties();

props.setProperty("prepareThreshold", "0");

Connection conn = DriverManager.getConnection(

"jdbc:postgresql://192.168.64.7:5432/testdb?user=user&password=password”, props);

Obtains “-1” all the times

You do give up the advantage of named statements which is that DESCRIBE won't be necessary, but that does appear to be less of a problem than returning a different representation.

Dave