Tag Archives: fsfo

When it comes to using Oracle, trust Oracle…

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A month ago, I saw this article published on the AWS architecture blog:

Disaster Recovery for Oracle Database on Amazon EC2 with Fast-Start Failover

I love seeing people suggesting Oracle Data Guard Fast-Start Failover for high availability. Nevertheless, there are a few problems with the architecture and steps proposed in the article.

I sent my comments via Disqus on the AWS blogging platform, but after a month, my comment was rejected, and the blog content hasn’t changed.

For this reason, I don’t have other places to post my comment but here…

  1. The link to the setup procedure is from 2009.
    We have official documentation that we keep up to date. The Fast-Start Failover part:
    https://docs.oracle.com/en/database/oracle/oracle-database/19/dgbkr/using-data-guard-broker-to-manage-switchovers-failovers.html#GUID-D26D79F2-0093-4C0E-98CD-224A5C8CBFA4
    and the Best Practices guide:
    https://docs.oracle.com/en/database/oracle/oracle-database/19/haovw/oracle-data-guard-best-practices.html#GUID-C3A78B07-6584-4380-8D53-E5B831A5894C
  2. The part about cascading standbys references a step-by-step guide from an external blog written many years ago for 11gR2.
  3. The DBMS_SERVICE doc is from 12cR1, while other links are from 21c doc or 19c doc. As of today, most implement 19c. That’s probably the version to use.
    https://docs.oracle.com/en/database/oracle/oracle-database/19/arpls/DBMS_SERVICE.html#GUID-C11449DC-EEDE-4BB8-9D2C-0A45198C1928
  4. The steps used to create the database service do not include any HA property, which will make most efforts useless. (see Table 153-6 in the link above).
  5. The article talks about TAF, but no steps exist to configure it. We don’t recommend TAF since 12c anyway. Today (19c), the recommendation is TAC (Transparent Application Continuity).
    https://www.oracle.com/docs/tech/application-checklist-for-continuous-availability-for-maa.pdf
  6. But, most important, TAF (or Oracle connectivity in general) does NOT require a host IP change! There is no need to change the DNS when using the recommended connection string with multiple address_lists.
  7. Some RedoRoutes examples are not correct. In this video I explain how they work and how to set them up:
    https://www.youtube.com/watch?v=huG8JPu_s4Q
  8. The diagram shows the master observer together with the standby database, which is a bad practice. I explain why and how here:
    https://www.youtube.com/watch?v=e81UPLfnLi0

The central message is:

If you need to implement a complex architecture using a software solution, pay attention that the practices suggested by the partner/integrator/3rd party match the ones from the software vendor. In the case of Oracle Data Guard, Oracle knows better 😉

Cheers

—

Ludovico

 

Far Sync and Fast-Start Failover Protection modes

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Oracle advertises Far Sync as a solution for “Zero Data Loss at any distance”. This is because the primary sends its redo stream synchronously to the Far Sync, which relays it to the remote physical standby.

There are many reasons why Far Sync is an optimal solution for this use case, but that’s not the topic of this post 🙂

Some customers ask: Can I configure Far Sync to receive the redo stream asynchronously?

Although a direct standby receiving asynchronously would be a better idea, Far Sync can receive asynchronously as well.

And one reason might be to send asynchronously to one Far Sync member that redistributes locally to many standbys.

It is very simple to achieve: just changing the RedoRoutes property on the primary.

This will work seamlessly. The v$dataguard_process will show the async transport process:

 

What about Fast-Start Failover?

Up to and including 19c, ASYNC transport to Far Sync will not work with Fast-Start Failover (FSFO).

ASYNC redo transport mandates Maximum Performance protection mode, and FSFO supports that in conjunction with Far Sync only starting with 21c.

Before 21c, trying to enable FSFO with a Far Sync will fail with:

So if you want FSFO with Far Sync in 19c, it has to be MaxAvailability (and SYNC redo transport to the FarSync).


If you don’t need FSFO, as we have seen, there is no problem. The only protection mode that will not work with Far Sync is Maximum Protection:

If FSFO is required, and you want Maximum Performance before 21c, or Maximum Protection, you have to remove Far Sync from the redo route.

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Ludovico