More about Dataguard and how to check it

Ludovico — Fri, 06 Feb 2009 11:27:51 +0000

After my post Quick Oracle Dataguard check script I have some considerations to add:
to check the gap of applied log stream by MRP0 process it’s sufficient to replace this query in the perl script I posted:

 SELECT SEQUENCE#, BLOCK# from v\$managed_standby
        WHERE process='RFS' AND client_process='LGWR'

with this new one:

 SELECT SEQUENCE#, BLOCK# from v\$managed_standby
        WHERE process='MRP0'

To check this you have to meet the following condition: You should have real-time apply enabled (and possibly NODELAY clause specified in your recover statement). Check it with this query:

SELECT RECOVERY_MODE FROM V$ARCHIVE_DEST_STATUS;

It should be “MANAGED REAL TIME APPLY”.
If not using realtime apply your MRP0 process will wait until you have a new archive, so even if you have redo transport mode set to LGWR you’ll wait for standby log completion. Your gap of applied redo stream will be at least one sequence#.

With transport mode set to LGWR and real-time apply the output of the perl script is similar to this one:

# ./checkDataGuard.sh
PROD   :       1230      20631
STANDBY:       1230      20613
18         blocks gap

The whole gap between your primary and standby database should be LOW.

Quick Oracle Dataguard check script

Ludovico — Mon, 05 Jan 2009 15:49:10 +0000

Oracle Dataguard has his own command-line dgmgrl to check the whole dataguard configuration status.
At least you should check that the show configuration command returns SUCCESS.

This is an hypothetic script:

#!/bin/bash
export ORACLE_HOME=/u1/app/oracle/product/10.2.0
export ORACLE_SID=orcldg
result=`echo "show configuration;" | \
  $ORACLE_HOME/bin/dgmgrl sys/strongpasswd | \
  grep -A 1 "Current status for" | grep -v "Current status for"`
if [ "$result" = "SUCCESS" ] ; then
    exit 0
else
    exit 1
fi

Another script should check for the gap between production online log and the log stream received by the standby database. This can be accomplished with v$managed_standby view.
The Total Block Gap between production and standby can be calculated this way:
Sum all blocks from v$archived_logs where seq# between Current Standby Seq# and Current Production Seq#. Then add current block# of the production LGWR process and subtract current block# from RFS standby process. This gives you total blocks even if there is a log sequence gap between sites.
This is NOT the gap of online log APPLIED to the standby database. THIS IS THE GAP OF ONLINE LOG TRANSMITTED TO THE STANDBY RFS PROCESS and can be used to monitor your dataguard transmission from production to disaster recovery environment.

This is an excerpt of such script (please take care that it does not check against RFS failures, so it can fails when RFS is not alive):

#!/u1/app/oracle/product/10.2.0/perl/bin/perl -w
use DBI;
use DBD::Oracle qw(:ora_session_modes);
# DB connection #
my $prod  = "orclprod";
my $stby = "orcldr";
my $prodh;
unless ($prodh = DBI->connect('dbi:Oracle:'.$prod,
  'sys', 'strongpassword',
  {PrintError=>0, AutoCommit => 0,
  ora_session_mode => ORA_SYSDBA}))  {
    print "Error connecting to DB: $DBI::errstr\n";
        exit(1);
}
$prodh->{RaiseError}=1;
 
my $stbyh;
unless ($stbyh = DBI->connect('dbi:Oracle:'.$stby,
  'sys', 'strongpassword',
  {PrintError=>0, AutoCommit => 0,
  ora_session_mode => ORA_SYSDBA}))  {
    print "Error connecting to DB: $DBI::errstr\n";
        $prodh->disconnect;
        exit(1);
}
$stbyh->{RaiseError}=1;
 
my $sth;
### query prod
$sth = $prodh->prepare( < <EOSQL );
        select SEQUENCE#, BLOCK# from v\$managed_standby
        where process='LGWR'
EOSQL
$sth->execute();
my ($psequence, $pblock) = $sth->fetchrow_array();
$sth->finish();
### query stdby
$sth = $stbyh->prepare( < <EOSQL );
        select SEQUENCE#, BLOCK# from v\$managed_standby
        where process='RFS' and client_process='LGWR'
EOSQL
$sth->execute();
my ($ssequence, $sblock) = $sth->fetchrow_array();
$sth->finish();
 
printf ("PROD   : %10d %10d\n", $psequence, $pblock);
printf ("STANDBY: %10d %10d\n", $ssequence, $sblock);
 
$sth = $stbyh->prepare( < <EOSQL );
        select nvl(sum(blocks),0)
        + $pblock - $sblock as BLOCK_GAP
    from v\$archived_log
        where sequence# between $ssequence and $psequence
EOSQL
$sth->execute();
my ($blockgap) = $sth->fetchrow_array();
$sth->finish();
printf ("%-10d blocks gap\n", $blockgap);
 
$stbyh->disconnect;
$prodh->disconnect;

Any comment is appreciated!

DBA survival BLOG » Oracle Dataguard

More about Dataguard and how to check it

Quick Oracle Dataguard check script