AlephZarro has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks.

I'm using DBD::Oracle to make a connection to our Oracle databases. The connection definition includes multiple hosts and a LOAD_BALANCE=on directive (the tnsnames.ora definition follows)

prod_01 =
 (DESCRIPTION = (ADDRESS_LIST = 
     (ADDRESS = (PROTOCOL = TCP)(HOST = rac-host01)(PORT = 1521))
     (ADDRESS = (PROTOCOL = TCP)(HOST = rac-host02)(PORT = 1521))
     (ADDRESS = (PROTOCOL = TCP)(HOST = rac-host03)(PORT = 1521))
     (ADDRESS = (PROTOCOL = TCP)(HOST = rac-host04)(PORT = 1521))
     (ADDRESS = (PROTOCOL = TCP)(HOST = rac-host05)(PORT = 1521))
     (ADDRESS = (PROTOCOL = TCP)(HOST = rac-host06)(PORT = 1521))
     (ADDRESS = (PROTOCOL = TCP)(HOST = db0-vip-01)(PORT = 1521))
     (ADDRESS = (PROTOCOL = TCP)(HOST = db0-vip-02)(PORT = 1521))
     (ADDRESS = (PROTOCOL = TCP)(HOST = db0-vip-03)(PORT = 1521))
     (LOAD_BALANCE = yes))
   (CONNECT_DATA =(SERVICE_NAME = production.example.com)))

My connections complete successfully but I'm having intermittent failures with the query I'm running (the same query will fail roughly 1 in 9 times).

#!/usr/bin/perl -w

use DBI;
use DBD::Oracle qw(:ora_types);
use Carp;
use strict;

my $dbh = DBI->connect(
    'dbi:Oracle:prod_01',
    $ENV{PROD_DB_USER},
    $ENV{PROD_DB_PASS}
    ) or croak "Unable to connect: $DBI::errstr";

my $sth = $dbh->prepare( "select * from prod.t_connection_ports order 
+by client_id" );

$sth->execute;

printf( "\n%-15s %10s %10s %10s   %-30s \n\n",
        "Client","Port","Client ID","Status","Machine ID");

while ( my $row = $sth->fetchrow_arrayref ) {
    printf( "%-15s %10s %10s %10s   %-30s \n",
            @$row[3],@$row[2],@$row[0],@$row[4],@$row[1]);
}

[download]

I'd like to interrogate the DBI database handle to identify which of the hosts in the definition list I've been connected to see if there's a correlation between a given host and the query failure.

Is there a way to identify the Oracle host to which I've been connected? I see nothing in DBI or DBD::Oracle docs which might give me this information.

Any pointers in the right direction would be greatly appreciated.

-- AZ

Replies are listed 'Best First'.
Re: Identify host connected to in DBD::Oracle connection?
by marto (Cardinal) on Sep 28, 2009 at 15:51 UTC

    Would doing something like select host_name from v$instance; be any help?

    Martin

[reply]
[d/l]
      Doesn't seem to allow querying the v$ views 
      DBD::Oracle::db prepare failed: ORA-00942: table or view does not exis
+t (DBD ERROR: error possibly near <*> indicator at char 22 in 'select
+ host_name from <*>v$instance')

      [download]
[reply]
[d/l]

        You will need to get your DBA to grant read only access to v$. Something like:

        grant select on sys.v_$instance to yourusername

        Either get them to do it or consult the Oracle documentation

        Martin

[reply]
[d/l]
Re: Identify host connected to in DBD::Oracle connection?
by kennethk (Abbot) on Sep 28, 2009 at 16:28 UTC
    I think you can get what you want from the Name attribute. From DBI:

    Holds the "name" of the database. Usually (and recommended to be) the same as the "dbi:DriverName:..." string used to connect to the database, but with the leading "dbi:DriverName:" removed.

    This can be accessed as:

    $handle->{Name}

    Update: Does not meet spec -> only accesses local value (see below).

[reply]
[d/l]
      Hi.

      print "Name: $dbh->{Name}\n"; returns Name: prod_01 which is the database name.

      I'm hoping I might be able to determine the hostname used for the connection (which one of the nine hosts listed in the tnsnames.ora definition was used for this connection).

[reply]
[d/l]
[select]
        That's what I get for reading too fast. How about trying a get_info call on SQL_SERVER_NAME? I've verified the following against an Oracle database I have access to, but not in a multiple hosts/load balance context. 

        #!/usr/bin/perl
use strict;
use warnings;
use DBI;
use DBI::Const::GetInfoType;

my $_db_name = 'host';
my $_db_user = 'name';
my $_db_pass = 'password';

my @_dbi_path = ("dbi:Oracle:$_db_name",$_db_user,$_db_pass);

my $handle = DBI->connect(  @_dbi_path,
                            {
                                PrintError => 1,
                                RaiseError => 0,
                                AutoCommit => 0
                            }
                        );

#print join "\n", sort keys %GetInfoType;
print $handle->get_info($GetInfoType{SQL_SERVER_NAME});

        [download]

        See DBI::Const::GetInfoType and get_info in DBI.

        Update: Still no dice -> in DBD::Oracle, this is just a synonym for $handle->{Name}, as is SQL_DATA_SOURCE_NAME.

[reply]
[d/l]
[select]

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