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EnterpriseDB: Create Subscription
Oracle Tips by Burleson
 

A Subscription defines the target and links the target database to the published source.  Enter the subscription name and connection information.  If the Publication Name drop down is empty, press the Load button to refresh the list.

Associate the subscription to the publication as shown in Figure 7.11.

Figure 7.11: Link Subscription to Publisher

Press Create to create the subscription.

Snapshot

Before turning on synchronization, a snapshot must be taken to create the replicated objects in the EnterpriseDB instance.  The snapshot copies all of the replicated structures, including indexes and other supporting objects.

For reporting, you may have different index requirements than you would in an Oracle OLTP or OLAP database.  After running the snapshot, you may drop and/or create any indexes that you feel may help performance.  Do not alter the structure of any replicated tables or you might break replication.

Examine any triggers that are copied and decide if they are needed in the replicated instance.  In most situations, they are not required.

You can get to the Taking Snapshot dialog (Figure 7.12) by right-clicking on the subscription identified above and choosing Take Snapshot.

Figure 7.12: Take Initial Snapshot

Press the Take Snapshot button and examine the output window for any errors before proceeding.  You will only need to take the snapshot one time.

Synchronize

A synchronization is the process of catching the target up with the source database.  Most forms of replication are to synchronize multiple instances.  You can get to the Synchronize dialog (Figure 7.13) by right-clicking on the subscription and selecting Synchronize.

Figure 7.13: Force a Synchronize

The synchronization process may run for several minutes depending on how much data is being synchronized.  Wait for a successful completion before moving on to the next step.

The Schedule

While it is possible to manually synchronize your databases, doing so kind of defeats the purpose of having an enterprise class replication tool.

You will probably want to schedule an automatic refresh.  Depending on your uses and needs, you may want a near, real-time refresh or a more relaxed refresh such as daily, weekly, or monthly.  You may also schedule refreshes via crontab.

A point to make is that replication is never truly real-time.  At best, transactions will experience some percentage of time delay.  It takes time to enqueue captured transactions at the source, propagate to the target and then apply them at the target. 

The Schedule Task Wizard (Figure 7.14) is the tool within the Replication Console that will allow you to schedule your replication jobs.

Figure 7.14: Configure Schedule

You may choose a complete refresh on each run (Snapshot) or you may choose to synchronize.  For this example, I will choose Synchronize.

As mentioned above, you may choose to schedule the replication continuously (near real-time), daily, weekly, monthly or via crontab.

For this example, I am choosing continuously (Figure 7.15) but I will display each of the other screens to give you an idea of the information required to fill them out.

Figure 7.15: Continuous Synchronization

In Continuous replication, you configure a refresh rate to gather and apply changes.  Remember that the more often you refresh, the heavier the load on both the source and the target databases.

For a Daily replication task (Figure 7.16), you define the hour and minute that you want to begin the synchronization.

Figure 7.16: Daily Synchronization

For a Weekly replication task (Figure 7.17), you define the hour and minute, as well as the days of the week that you want to begin the synchronization.

Figure 7.17:  Weekly Synchronization

For a Monthly replication task (Figure 7.18), you define the hour and minute, the day of the month and which months that you want to begin the synchronization.

Figure 7.18: Monthly Synchronization

For crontab scheduling (Figure 7.19), you must define a valid crontab expression.  You must also have cron running to schedule jobs via cron.

Figure 7.19: Cron Synchronization

After successfully defining the scheduling method you require, press the Next button to arrive at the Schedule Summary dialog (Figure 7.20).  Verify that the summary accurately reflects your choices and press the Finish button.

Figure 7.20: Complete Schedule

Once the schedule has been defined, the replication server will ensure that it executes the data movement as scheduled.  You can view the replication log and real-time monitor by clicking to the lowest node beneath the subscription service.


     

This is an excerpt from the book "EnterpriseDB: The Definitive Reference" by Rampant TechPress.

  
 

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