Re: ODBC cliens is hanging if network connection is broken

On 2018/07/09 23:06, [email protected] wrote:
> Hello!
>
> Thank You for quick response.
> I set *SQL_ATTR_QUERY_TIMEOUT*to 5 seconds as follows:
>
> SQLRETURN rc = SQLSetStmtAttr(hstmt, SQL_ATTR_QUERY_TIMEOUT, 
> (SQLPOINTER) 5, SQL_IS_UINTEGER);
> after SQLAllocHandle for hstmt and before SQLExecDirect call.
>
> To take some time in SQLExecDirect I call the command "*SELECT 
> pg_sleep(10)*".
> If an ODBC aplication does not loose network connection with the 
> remote server  this command is terminated in 5 seconds after its 
> invocation.
> I get the following error *57014 *(*Cancelling statement due to 
> statement timeout*).
>
> In case if network connection is lost(network interface is down) my 
> ODBC application is indefinitely hanging.
> Here is a gstack output of this process:
> *gstack 13359*
> #0  0x00007fdd045703b0 in __poll_nocancel () from /lib64/libc.so.6
> #1  0x00007fdd037c8626 in ?? () from /usr/lib64/libpq.so.5
> #2  0x00007fdd037c86b0 in ?? () from /usr/lib64/libpq.so.5
> #3  0x00007fdd037c6889 in PQgetResult () from /usr/lib64/libpq.so.5
> #4  0x00007fdd039fbe55 in CC_send_query_append 
> (self=self@entry=0x10ccc60, query=query@entry=0x7fff2364d470 "SET 
> statement_timeout = 5000", qi=qi@entry=0x0, flag=flag@entry=0, 
> stmt=stmt@entry=0x0, appendq=appendq@entry=0x0) at connection.c:1921
> #5  0x00007fdd03a2e3ed in SC_execute (self=self@entry=0x10df840) at 
> statement.c:1912
> #6  0x00007fdd03a0c596 in Exec_with_parameters_resolved 
> (stmt=stmt@entry=0x10df840, exec_end=exec_end@entry=0x7fff2364d60c) at 
> execute.c:450
> #7  0x00007fdd03a0d4b6 in PGAPI_Execute (hstmt=hstmt@entry=0x10df840, 
> flag=flag@entry=1) at execute.c:1045
> #8  0x00007fdd03a0daac in PGAPI_ExecDirect 
> (hstmt=hstmt@entry=0x10df840, szSqlStr=szSqlStr@entry=0x4014ed "SELECT 
> pg_sleep(10)", cbSqlStr=cbSqlStr@entry=-3, flag=flag@entry=1) at 
> execute.c:191
> #9  0x00007fdd03a3511b in SQLExecDirect (StatementHandle=0x10df840, 
> StatementText=0x4014ed "SELECT pg_sleep(10)", TextLength=-3) at 
> odbcapi.c:322
> #10 0x00007fdd04851432 in SQLExecDirect () from /usr/lib64/libodbc.so.2
> #11 0x0000000000400fcf in main (argc=1, argv=0x7fff2364d928) at 
> odbcExample.c:163
>
> Do you have any idea what can be wrong?
>
> Thank you in advance,
> Andrei Yahorau
>
>
>
> From: "Inoue, Hiroshi" <[email protected]>
> To: [email protected],
> Cc: [email protected], [email protected]
> Date: 08/07/2018 13:33
> Subject: Re: ODBC cliens is hanging if network connection is broken
> ------------------------------------------------------------------------
>
>
>
> Hi,
>
> On 2018/07/07 21:37, [email protected]_ 
> <mailto:[email protected]>wrote:
> Hello PostgreSQL Community!
>
> I downloaded and installed the latest version of PostgreSQL from 
> _https://www.postgresql.org/ftp/source/v10.4/_on my SLES 12 system.
> Here is my configuration of unixODBC:
>
> odbcinst,ini
> [PostgreSQL]
> Description=PostgreSQL ODBC driver
> Driver=/usr/local/lib/psqlodbcw.so
> FileUsage=1
>
> odbc.ini
> [sles12-1]
> Description = PostgreSQL connection to rtpdb
> Driver = PostgreSQL
> Database = rtpdb
> Servername = sles12-1
> Username =
> Password =
> Port = 5432
> Protocol = 7.4+
> ReadOnly = No
> RowVersioning = No
> ShowSystemTables = No
> ConnSettings =
>
> As a Driver in odbcinst.ini I specified the path to *psqlodbcw.so 
> *which was downloaded from 
> _https://git.postgresql.org/gitweb/?p=psqlodbc.git_and built as follows:
> ./configure
> make
> make install
>
> Could you please provide a comment concerning the following situation?
>
> I  created a simple ODBC program which calls "*SELECT 
> pg_is_in_recovery()*" on the remote PostgreSQL server using ODBC API. 
> It works good with this ODBC configuration. But as soon as I turn off 
> network interface after *SQLConnect *call and before *SQLExecDirect*, 
> it leads to *SQLExecDirect *hanging.
>
> I tried to use *statement_timeout* and 
> *idle_in_transaction_session_timeout* postgresql configuration 
> parameters but they were not suitable for network issue case. These 
> parameters define server-side behaviour but a client considers that 
> the connection is ok and it is hanging.
>
>
>
> As far as I know *SQL_ATTR_CONNECTION_TIMEOUT *ODBC attribute could 
> handle this situation. Another ODBC driver for another database in 
> case of similar situation returns *HYT01 *ODBC error (Connection 
> timeout expired) . But I guess *SQL_ATTR_CONNECTION_TIMEOUT * is not 
> supported by psqlodbc.  Am I right?
>
> How about calling SQLSetStmtAttr() with the attribute parameter 
> SQL_ATTR_QUERY_TIMEOUT?
>
>
>
> PostgreSQL JDBC driver provides *socketTimeout*property which helps a 
> client to be informed about network problems and to avoid an infinite 
> hanging.
> In my tests it returned *08006 *sqlstate (*connection_failure*).
>
> So I have a question. Is there any psqlodbc or native PostgreSQL 
> mechanism or configuration parameter which helps a client to be 
> informed about network problem?
> Is there any mechanism which helps to avoid this infinite hanging for 
> SQL query in this case?

Could you try options about TCP keepalive using pqopt in odbc.ini

pqopt = |keepalives=1 |||keepalives_interval=5 |||||keepalives_count=1

?

regards,
Hiroshi Inoue

|||
>
>
> Thank You in advance,
> Andrei Yahorau