Ilmar Kerm

Oracle, databases, Linux and maybe more

I recently had an interesting challenge to direct data guard network traffic over a dedicated network interface and not go though the main network routes. The reason was that in order to reach the remote datacenter, the dataguard traffic should be sent via WAN optimizer network, that will automatically compress and dedup all traffic (hard to believe, that there are still some places left in Europe, where internet bandwidth is extremely expensive). I know that Oracle since 11.2 can do redo compression for data guard traffic also, but this requires advanced compression option and also uses database host CPU-s to do the compression, WAN optimizer software licenses are cheaper and usable for other tasks as well.

The following tasks need to be completed:

  1. Configure a new network interface in OS. I’m not going to discuss it here, but it is a prerequisite for any tasks to be done in Oracle.
  2. Configure the new network for Oracle listener. If you are using standalone database and haven’t got some special configuration for you listener, then it should already listen on the new network interface also. RAC needs special attention and it is described in this blog post. Basically you need to configure new set of VIP addresses, create a new network resource in clusterware and configure database instance to register on the new network. SCAN address cannot be created on the additional network.
  3. Configure Data Guard to communicate over the newly created network. The necessary steps are described below and I’m assuming that Data Guard Broker is in use.

My database setup is the following: primary database is RAC (prd_db_rac) and it has two physical standbys, one local (prd) and one remote (prd_wan1).

$ ORACLE_SID=prd dgmgrl /
DGMGRL for Linux: Version - 64bit Production

Copyright (c) 2000, 2009, Oracle. All rights reserved.

Welcome to DGMGRL, type "help" for information.
DGMGRL> show configuration

Configuration - prd

  Protection Mode: MaxPerformance
    prd_db_rac - Primary database
    prd        - Physical standby database
    prd_wan1   - Physical standby database

Fast-Start Failover: DISABLED

Configuration Status:

Now lets look at the properties of one of the databases.

DGMGRL> show database verbose prd_wan1;

Database - prd_wan1

  Enterprise Manager Name:
  Role:                    PHYSICAL STANDBY
  Intended State:          APPLY-ON
  Transport Lag:           0 seconds (computed 1 second ago)
  Apply Lag:               0 seconds (computed 0 seconds ago)
  Apply Rate:              3.08 MByte/s
  Real Time Query:         ON

    DGConnectIdentifier             = '//'
    ObserverConnectIdentifier       = ''
    LogXptMode                      = 'ASYNC'
    DelayMins                       = '0'
    Binding                         = 'optional'
    MaxFailure                      = '0'
    MaxConnections                  = '1'
    ReopenSecs                      = '300'
    NetTimeout                      = '30'
    RedoCompression                 = 'DISABLE'
    LogShipping                     = 'ON'
    PreferredApplyInstance          = ''
    ApplyInstanceTimeout            = '0'
    ApplyParallel                   = 'AUTO'
    StandbyFileManagement           = 'AUTO'
    ArchiveLagTarget                = '0'
    LogArchiveMaxProcesses          = '4'
    LogArchiveMinSucceedDest        = '1'
    DbFileNameConvert               = ''
    LogFileNameConvert              = ''
    FastStartFailoverTarget         = ''
    InconsistentProperties          = '(monitor)'
    InconsistentLogXptProps         = '(monitor)'
    SendQEntries                    = '(monitor)'
    LogXptStatus                    = '(monitor)'
    RecvQEntries                    = '(monitor)'
    ApplyLagThreshold               = '0'
    TransportLagThreshold           = '0'
    TransportDisconnectedThreshold  = '30'
    SidName                         = 'prd'
    StaticConnectIdentifier         = '(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)('
    StandbyArchiveLocation          = 'USE_DB_RECOVERY_FILE_DEST'
    AlternateLocation               = ''
    LogArchiveTrace                 = '0'
    LogArchiveFormat                = '%t_%s_%r.dbf'
    TopWaitEvents                   = '(monitor)'

Database Status:

Each database in the broker configuration has a property telling how other databases in the same broker configuration can connect and send redo to it. This parameter is the first on the list – DGConnectIdentifier. All we need to do is change this property to point to an address in the new network. For single instance databases this is easy task, we can use the easy connect syntax, so for my case need to change the physical standby connection string as follows (sb. prefix in host names are located in the new wan optimized network).

DGMGRL> EDIT DATABASE prd SET PROPERTY 'DGConnectIdentifier'='//';
Property "DGConnectIdentifier" updated.

DGMGRL> EDIT DATABASE prd_wan1 SET PROPERTY 'DGConnectIdentifier'='//';
Property "DGConnectIdentifier" updated.

The same property needs to be changed for primary database also, but short SCAN address cannot be created for the secondary network and in broker the property value string cannot be long enough to hold the full RAC connection string for my configuration. So I needed to add the following entry to tnsnames.ora for all Oracle Homes involved in that configuration (both primary and all standbys). Here again, sb part of the DNS name refers to IP on the new network.

      (ADDRESS= (PROTOCOL = TCP)(HOST = = 1521))
      (ADDRESS= (PROTOCOL = TCP)(HOST = = 1521))
      (ADDRESS= (PROTOCOL = TCP)(HOST = = 1521))
      (ADDRESS= (PROTOCOL = TCP)(HOST = = 1521))
      (FAILOVER = on)

Now I can make the same Broker property change for primary RAC database also.

Property "DGConnectIdentifier" updated.

That was all, no need to restart anything, after property change Broker changes automatically the instance parameters itself. We did this change in order to replace the old SAN based replication to remote datacenter with Data Guard and to save on bandwidth we needed to run the Data Guard traffic through separate WAN optimized network. On the average we see that the WAN optimizer compresses Data Guard traffic about 3-4 times and compared to the old SAN replication setup (SAN did compress the change log also internally before sending it to the remote site) we use about 2 times less bandwidth (or actually more, since we were previously limiting SAN replication bandwidth, during the day it always ran on the limit and caught up during the night). Considering how much internet bandwidth costs on some places, the extra Data Guard license needed will pay for itself in surprisingly short time in reduced Internet bandwidth alone (not calculating the extra features it also brings, like Active Data Guard).