You MUST patch and and older databases before June 2019

First of all, this blog post is not new. I blogged about this SCN topic a while ago already. But some of you seem to operate still older databases for various reasons. And even if you think that you are safe, double check for any older databases in your environments. You MUST patch and and older databases before June 23, 2019. And just to be clear: June 23, 2019 is going to happen in less than 4 months.

You MUST patch and and older databases before June 2019

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Who is NOT affected?

If you use the following Oracle database releases exclusively, you are NOT affected:

  • Oracle Database and newer (including Oracle, Oracle 18c and Oracle 19c)
  • Oracle Database
  • Oracle Database with at least Jan 2014 PSU/BP
  • Oracle Database with at least Jul 2014 PSU/BP
  • On MS Windows:
    • with at least Patch 29 (Feb 2014)
    • with at least Patch 57 (Jul 2014)

And of course, if your databases don’t use database links, this issue may not affect you either.

But if you use database links to databases of releases below the ones I did mention, you must patch.

Or upgrade in some cases. Especially in cases where you use “buffer” databases such as connecting an Oracle 9i database to an Oracle database in order to pull data from an Oracle databases.

What is the technical background?

At any point in time, the Oracle Database calculates a “not to exceed” limit for the number of SCNs a database can have used, based on the number of seconds elapsed since 1988. This is known as the database’s current maximum SCN limit. When you open a database link between two databases, the SCN needs to be synced between the two. If one of the two databases is unpatched, then it can happen that the SCN increase needed in the unpatched database for this sync is beyond it’s allowed SCN rate or current max SCN limit. In this case the database link connection cannot be established.

This issue can arise after June 23, 2019.

If you need more information in addition to MOS Note: 2335265.1, you will find an excellent technical summary here on Job Oprel‘s blog:

What are the patches implementing?

These recommended patches enable the databases to allow for a higher current maximum SCN limit. The rate at which this limit is calculated can be referred to as the “SCN rate” and these patches help allow higher SCN rates to enable databases to support many times higher transaction rates than earlier releases.

Please note that the patches only increase the max limit but the current SCN is not impacted. So, if all your databases don’t have any major change in transaction rate, the current SCN would still remain below the current maximum SCN limit and database links between newer (or patched) and unpatched databases would continue to work. The patches provide the safety measure to ensure that you don’t have any issue with database links independent of any possible future change in your transaction rate.

If this patch is not applied, the unpatched database will have a lower SCN rate or lower current max SCN limit.
The newer or patched databases will have higher SCN rate or higher current max SCN limit.

What is the risk of NOT patching?

You should be aware about potential database link issues in future and consider about upgrading the databases or not using database links with newer versions of databases . If you continue to have such database links after June 2019, you may get run-time errors during database link operations and you would need to disconnect those database links at that time.

Where do you find more information?

Here you’ll find a lot more information:


PS: An addition as of March 10, 2019:

Initially the blog post listed this release as not affected:

  • Oracle Database with Jan 2017 PS

But in fact the patch is not included in this PSU. Hence, Oracle 10.2 is always affected by this issue. Even if you are on the highest patch level for Sorry for the inconvenience. The MOS Note the information was taken from should have been corrected as well by now.

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4 thoughts on “You MUST patch and and older databases before June 2019

  1. Hello Mike!

    I know this could be a stupid question, but I decide to raise it anyway.
    Does this all mean that all 11g XE installations are affected by this issue (11g XE for Linux and Windows was based on And that there is no other possibility to overcome it, but to migrate them to the newer 18c XE?

    • Hi Denis,

      it’s a very valid question. When you connect to or from an XE database to a patched one, for instance an SE2 database, then you’ll be potentially affected.

      Your upgrade path would be:
      expdp from current XE
      download new 18c XE for either Win or Linux (see the blog here)
      impdp into an 18c XE

      That’s it.


  2. Hi Mike ,
    We have Oracle 11g and 12c databases, some are on Exadata.
    Since Oracle has changed the versioning model (one version per year), I would like to know what is the right/best strategy for managing the obsolescence of our databases and the migration to 18c and 19c.
    Best regards.

    • GD,

      not sure about your question. We changed the release numbering but 18c is, and 19c will be
      Hence, there’s not much of a change right now. We expect most software vendors to certify on 19c as this is the long term support release going until 2026.

      Please see the slide deck about the release strategy on
      This will give you more insights.


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