real-time apply - DBA survival BLOG

Two years after my posts:
Quick Oracle Dataguard check script and More about Dataguard and how to check it I faced a whole new Dataguard between two Oracle Real Application Clusters, aka Oracle Maximum Availability Architecture (MAA).

This enviromnent is relying on Windows OS. Don’t know how this could be called “availability” but here we are. I revisited my scripts in a quick and very dirty way. Please consider that I did copy and paste to check the alignment once per thread, but it should be improved with some kind of iteration to check each thread in a more structured fashion.

#!D:\oracle\product\10.2.0\db_1\perl\5.8.3\bin\MSWin32-x86-multi-thread\perl.exe -w
use DBI;
use DBD::Oracle qw(:ora_session_modes);
# DB connection #
my $prod  = "prod";
my $stby = "stby";
my $prodh;
unless ($prodh = DBI-&gt;connect('dbi:Oracle:'.$prod, 
    'sys', 'strongpwd', 
    {PrintError=&gt;0, AutoCommit =&gt; 0,
    ora_session_mode =&gt; ORA_SYSDBA}))  {
print "Error connecting to DB: $DBI::errstr\n";
exit(1);
}
$prodh-&gt;{RaiseError}=1;

my $stbyh;
unless ($stbyh = DBI-&gt;connect('dbi:Oracle:'.$stby,
    'sys', 'strongpwd',
    {PrintError=&gt;0, AutoCommit =&gt; 0,
    ora_session_mode =&gt; ORA_SYSDBA}))  {
print "Error connecting to DB: $DBI::errstr\n";
$prodh-&gt;disconnect;
exit(1);
}
$stbyh-&gt;{RaiseError}=1;

my $sth;
### query stdby MRP0
$sth = $stbyh-&gt;prepare( &lt;&lt;EOSQL );
select thread#, SEQUENCE#, BLOCK#
    from gv\$managed_standby 
    where process='MRP0'
EOSQL
$sth-&gt;execute();
my ($mrpthread, $mrpsequence, $mrpblock) = $sth-&gt;fetchrow_array();
$sth-&gt;finish();

### query stdby RFS
$sth = $stbyh-&gt;prepare( &lt;&lt;EOSQL );
select thread#, SEQUENCE#, BLOCK#
    from gv\$managed_standby 
    where process='RFS' and client_process='LGWR' order by thread#
EOSQL
$sth-&gt;execute();
my ($rfsthread1, $rfssequence1, $rfsblock1) = $sth-&gt;fetchrow_array();
my ($rfsthread2, $rfssequence2, $rfsblock2) = $sth-&gt;fetchrow_array();
$sth-&gt;finish();

### query prod
$sth = $prodh-&gt;prepare( &lt;&lt;EOSQL );
select thread#, SEQUENCE#, BLOCK#
    from gv\$managed_standby
    where process='LNS' order by thread#
EOSQL
$sth-&gt;execute();
my ($pthread1, $psequence1, $pblock1) = $sth-&gt;fetchrow_array();
my ($pthread2, $psequence2, $pblock2) = $sth-&gt;fetchrow_array();
$sth-&gt;finish();


printf ("ENVIRONM  Thread Sequence   Block\n");
printf ("--------- ------ ---------- ----------\n");
printf ("PROD     LNS1  1 %10d %10d\n", $psequence1, $pblock1);
printf ("STANDBY  RFS1  1 %10d %10d\n", $rfssequence1, $rfsblock1);
printf ("PROD     LSN2  2 %10d %10d\n", $psequence2, $pblock2);
printf ("STANDBY  RFS2  2 %10d %10d\n", $rfssequence2, $rfsblock2);
printf ("STANDBY  MRP0  %d %10d %10d\n", $mrpthread, $mrpsequence, $mrpblock);

my $psequence;
my $pblock;
if ( $mrpthread == 1 ) {
$psequence=$psequence1;
$pblock=$pblock1;
} else {
$psequence=$psequence2;
$pblock=$pblock2;
}

$sth = $stbyh-&gt;prepare( &lt;&lt;EOSQL );
select nvl(sum(blocks),0)
+ $pblock - $mrpblock as BLOCK_GAP
from gv\$archived_log
where thread#=$mrpthread and sequence#
between $mrpsequence and $psequence
EOSQL
$sth-&gt;execute();
my ($mrpblockgap) = $sth-&gt;fetchrow_array();
$sth-&gt;finish();

$sth = $stbyh-&gt;prepare( &lt;&lt;EOSQL );
select nvl(sum(blocks),0)
+ $pblock1 - $rfsblock1 as BLOCK_GAP
from gv\$archived_log
where thread#=1 and sequence#
between $rfssequence1 and $psequence1
EOSQL
$sth-&gt;execute();
my ($rfsblockgap1) = $sth-&gt;fetchrow_array();
$sth-&gt;finish();

$sth = $stbyh-&gt;prepare( &lt;&lt;EOSQL );
select nvl(sum(blocks),0)
+ $pblock2 - $rfsblock2 as BLOCK_GAP
from gv\$archived_log
where thread#=2 and sequence#
between $rfssequence2 and $psequence2
EOSQL
$sth-&gt;execute();
my ($rfsblockgap2) = $sth-&gt;fetchrow_array();
$sth-&gt;finish();
printf ("\n\n%-10d blocks gap in TRANSMISSION\n", $rfsblockgap1+$rfsblockgap2);
printf ("%-10d blocks gap in APPLY (MRP0)\n", $mrpblockgap);

$stbyh-&gt;disconnect;
$prodh-&gt;disconnect;

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#!D:\oracle\product\10.2.0\db_1\perl\5.8.3\bin\MSWin32-x86-multi-thread\perl.exe -w

use DBI;

use DBD::Oracle qw(:ora_session_modes);

# DB connection #

my $prod = "prod";

my $stby = "stby";

my $prodh;

unless ($prodh = DBI->connect('dbi:Oracle:'.$prod,

'sys', 'strongpwd',

{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', 'strongpwd',

{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 stdby MRP0

$sth = $stbyh->prepare( <<EOSQL );

select thread#, SEQUENCE#, BLOCK#

from gv\$managed_standby

where process='MRP0'

EOSQL

$sth->execute();

my ($mrpthread, $mrpsequence, $mrpblock) = $sth->fetchrow_array();

$sth->finish();

### query stdby RFS

$sth = $stbyh->prepare( <<EOSQL );

select thread#, SEQUENCE#, BLOCK#

from gv\$managed_standby

where process='RFS' and client_process='LGWR' order by thread#

EOSQL

$sth->execute();

my ($rfsthread1, $rfssequence1, $rfsblock1) = $sth->fetchrow_array();

my ($rfsthread2, $rfssequence2, $rfsblock2) = $sth->fetchrow_array();

$sth->finish();

### query prod

$sth = $prodh->prepare( <<EOSQL );

select thread#, SEQUENCE#, BLOCK#

from gv\$managed_standby

where process='LNS' order by thread#

EOSQL

$sth->execute();

my ($pthread1, $psequence1, $pblock1) = $sth->fetchrow_array();

my ($pthread2, $psequence2, $pblock2) = $sth->fetchrow_array();

$sth->finish();

printf ("ENVIRONM Thread Sequence Block\n");

printf ("--------- ------ ---------- ----------\n");

printf ("PROD LNS1 1 %10d %10d\n", $psequence1, $pblock1);

printf ("STANDBY RFS1 1 %10d %10d\n", $rfssequence1, $rfsblock1);

printf ("PROD LSN2 2 %10d %10d\n", $psequence2, $pblock2);

printf ("STANDBY RFS2 2 %10d %10d\n", $rfssequence2, $rfsblock2);

printf ("STANDBY MRP0 %d %10d %10d\n", $mrpthread, $mrpsequence, $mrpblock);

my $psequence;

my $pblock;

if ( $mrpthread == 1 ) {

$psequence=$psequence1;

$pblock=$pblock1;

} else {

$psequence=$psequence2;

$pblock=$pblock2;

}

$sth = $stbyh->prepare( <<EOSQL );

select nvl(sum(blocks),0)

+ $pblock - $mrpblock as BLOCK_GAP

from gv\$archived_log

where thread#=$mrpthread and sequence#

between $mrpsequence and $psequence

EOSQL

$sth->execute();

my ($mrpblockgap) = $sth->fetchrow_array();

$sth->finish();

$sth = $stbyh->prepare( <<EOSQL );

select nvl(sum(blocks),0)

+ $pblock1 - $rfsblock1 as BLOCK_GAP

from gv\$archived_log

where thread#=1 and sequence#

between $rfssequence1 and $psequence1

EOSQL

$sth->execute();

my ($rfsblockgap1) = $sth->fetchrow_array();

$sth->finish();

$sth = $stbyh->prepare( <<EOSQL );

select nvl(sum(blocks),0)

+ $pblock2 - $rfsblock2 as BLOCK_GAP

from gv\$archived_log

where thread#=2 and sequence#

between $rfssequence2 and $psequence2

EOSQL

$sth->execute();

my ($rfsblockgap2) = $sth->fetchrow_array();

$sth->finish();

printf ("\n\n%-10d blocks gap in TRANSMISSION\n", $rfsblockgap1+$rfsblockgap2);

printf ("%-10d blocks gap in APPLY (MRP0)\n", $mrpblockgap);

$stbyh->disconnect;

$prodh->disconnect;

Please foreward me every improvement you implement over my code: it would be nice to post it here.

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'

1 2	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'

1 2	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;

1	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

# ./checkDataGuard.sh

PROD : 1230 20631

STANDBY: 1230 20613

18 blocks gap

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

DBA survival BLOG

Some DBA stuff and lots of Oracle Data Guard

Tag Archives: real-time apply

Dataguard check script for Real Application Clusters (MAA)

More about Dataguard and how to check it