Re: [ODBC] ODBC connections go dead after a failed query?

On 03/03/2017 12:14 PM, Jack C. Wei wrote:

Hi,

We have some legacy SQL queries that works on SQL Server but not on
PostgreSQL due to SQL Server-specific syntax, which we are working to
migrate. The problem is sometimes psqlodbc just cannot seem to reset
itself after a bad query and simply go dead. All subsequent queries on
the same connection, legitimate or not, would fail.

I've verified this can happen with the latest PostgreSQL 9.6.2 and
psqlodbc 09_06_0100, on a Windows 7 x64 host.

The offending SQL query is something like "UPDATE site SET
image=image_old;" where [image] is BYTEA (used to be MEDIUMBLOB on SQL
Server) and [image_old] is TEXT. PostgreSQL does not allow this, which
is understandable. But after this query the connection goes dead,
failing all subsequent queries with ODBC error 08S01 or HY000. While it
is possible to detect this and reconnect as a workaround, it would be
cumbersome and lead to unwarranted overhead. See the following excerpt
from my ODBC trace log:


PsqlOdbcBug     f68-e10    EXIT  SQLPrepareW  with return code 0
(SQL_SUCCESS)
        HSTMT               0x00033EE8
        WCHAR *             0x010F0F28 [      -3] "UPDATE site SET
image=image_old;\ 0"
        SDWORD                    -3

PsqlOdbcBug     f68-e10    ENTER SQLExecute
        HSTMT               0x00033EE8

PsqlOdbcBug     f68-e10    EXIT  SQLExecute  with return code -1 (SQL_ERROR)
        HSTMT               0x00033EE8

        DIAG [42804] ERROR: column "image" is of type bytea but
expression is of type text;
Error while preparing parameters (1)

PsqlOdbcBug     f68-e10    ENTER SQLFreeHandle
        SQLSMALLINT                  3 <SQL_HANDLE_STMT>
        SQLHANDLE           0x00033EE8

PsqlOdbcBug     f68-e10    EXIT  SQLFreeHandle  with return code 0
(SQL_SUCCESS)
        SQLSMALLINT                  3 <SQL_HANDLE_STMT>
        SQLHANDLE           0x00033EE8

PsqlOdbcBug     f68-e10    ENTER SQLAllocHandle
        SQLSMALLINT                  3 <SQL_HANDLE_STMT>
        SQLHANDLE           0x000338D8
        SQLHANDLE *         0x0035EB90

PsqlOdbcBug     f68-e10    EXIT  SQLAllocHandle  with return code 0
(SQL_SUCCESS)
        SQLSMALLINT                  3 <SQL_HANDLE_STMT>
        SQLHANDLE           0x000338D8
        SQLHANDLE *         0x0035EB90 ( 0x00D51C98)

PsqlOdbcBug     f68-e10    ENTER SQLPrepareW
        HSTMT               0x00D51C98
        WCHAR *             0x010F0DE0 [      -3] "SELECT id FROM site;\ 0"
        SDWORD                    -3

PsqlOdbcBug     f68-e10    EXIT  SQLPrepareW  with return code 0
(SQL_SUCCESS)
        HSTMT               0x00D51C98
        WCHAR *             0x010F0DE0 [      -3] "SELECT id FROM site;\ 0"
        SDWORD                    -3

PsqlOdbcBug     f68-e10    ENTER SQLExecute
        HSTMT               0x00D51C98

PsqlOdbcBug     f68-e10    EXIT  SQLExecute  with return code -1 (SQL_ERROR)
        HSTMT               0x00D51C98

        DIAG [08S01] Could not send Query(connection dead);
Could not send Query(connection dead) (26)


I've attached a minimal working sample code (we develop in Visual Studio
2013) and also the ODBC trace log. Hopefully they make it through. Any
feedback is welcome.

I am betting you dealing with something like this:

test=> begin ;
BEGIN
test=> select 1/0;
ERROR:  division by zero
test=> select 1;
ERROR:  current transaction is aborted, commands ignored until end of transaction block
test=> rollback ;
ROLLBACK
test=> select 1;
 ?column?
----------
        1
(1 row)

Basically an error in a transaction stops everything until you rollback.

Here:
https://odbc.postgresql.org/docs/config.html

there is :

Level of rollback on errors: Specifies what to rollback should an error occur.


    Nop(0): Don't rollback anything and let the application handle the error.

    Transaction(1): Rollback the entire transaction.

    Statement(2): Rollback the statement.


    Notes in a setup: This specification is set up with a PROTOCOL option parameter.

    PROTOCOL=[6.2|6.3|6.4|7.4][-(0|1|2)]
    default value is a sentence unit (it is a transaction unit before 8.0).

I have never used that, so I am not sure exactly how  to invoke it and what the consequences are.

Thank you,
Jack Wei

--
Adrian Klaver
adrian.klaver@aklaver.com