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
  • Oracle Database with at least Oct 2017 PSU and Patch 14121009 on top
  • 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:

And of course, Frits Hoogland has dug muuuuuch deeper and came around with this long post:

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.

What should you do now?

For owners of a large number of databases, across earlier versions, where you are not able to patch or upgrade and these databases use dblinks with very databases of newer releases, please contact Oracle Support immediately for guidance.

If you are in doubt, if you have older database releases still in use, please do the following:

  • Open a Service Request with Oracle Support and ask for guidance
  • You may check beforehand with the information provided on Frits Hoogland’s blog for SCN headroom
  • You may also use the Community Forum to discuss with the experts: Oracle Community Discussion

I really can’t give you advice on this. I can alert you about the issue. But clarification, advice etc need to come from Oracle Support.

Where do you find more information?

Here you’ll find a lot more information:


PS: Please ignore the change from March 10, 2019 – here’s another addition as of Apr 16, 2019:

It turned out that a conflicting patch for Oracle which was needed on top of the October 2017 PSU got re-released. Hence, with the combination of the October 2017 PSU for Oracle plus Patch 14121009 on top of it, the issue is fixed as well.

I keep the below PS from March 10, 2019, for the records only – it is not correct anymore.

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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12 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.


  3. Hi Mike,

    you stated recently, in a quick addition, that there’s no PSU available for The first docs from Oracle stated that a special PSU (, which means OCT-2017, and not JAN-2017) would be available.

    Accordingly to the MOS notes 2335265.1 and 2361478.1 (checked today) this PSU (along with interim patch 14121009) would still correct the problem in

    Easy links:

    So, these MOS notes still state as a “patchable” version for the 23-JUN db_link armageddon.

    Best regards,
    Luis Santos

    • Luis,

      I’m puzzled now as well. Support experts told me that there’s no such patch for That’s why I made the note in March on the blog post.
      But now I read the note again – and indeed it has a patch.

      Let me check that – and thanks for bringing this to my attention. I will update the blog post as soon as a receive a clarification.

      Thanks (and sorry if I misinformed you – not my intention, I just reproduce information in this case)

    • Luis,

      again big thanks – I could clarify and update the blog post.

      Here’s what has happened:
      1) The initial MOS document proposed that with PSU xyz and patch abc would fix the issue
      2) I’ve got alerted by support people that the MOS note is wrong, the single patch conflicts – and hence, can’t be applied.
      3) Now based on your finding, I realized that the conflicting Patch 14121009 which is needed on top of the Oct 2017 PSU for works now and can be applied.

      Hence, there’s a fix available (except on Windows) for as well.

      Thanks again!


      • Thanks for your kindly reply, Mike.

        There is new news! If you go the download page for OCT-2017 PSU for, aka patch 26493118, you will not the following message:

        This Patchset has been Superseded.
        Patch 26925212 is a super set of patch 26493118

        Here is the link:

        But, strangely, in the best DOC for the 23-JUN db_link armageddon (Doc ID 2361478.1, which was updated on 5-Apr-2019 with this important note: “Added patch details on top of”) it still recommends the old 26493118/OCT-2017 patch…

        This is very weird. And we have just one month and 10 days up to the armaggedon day.

        I was thinking if Oracle has forgot to update the DOC ID 2361478.1.

        And if the newer, updated PSU JUL-2018, would include Patch 14121009, making it the only necessary patch to get rid of the db_link SCN interconnect problem on old version.

        • Luis,

          I’m pretty sure “somebody” has forgotten the update – and I’ll send an email to the appropriate people while I write this to you.

          Thanks and sorry for the inconvenience!

          • Luis,

            here’s the “official” statement – the note should be more clear now:

            1. Patch 26925212 supersedes 26493118 in PSU terms
            2. BUT … SCN fixes were made only on 26493118.
            3. Patch 26925212 does not include the fix. It was specifically built for MDS customers and cannot be provided to all customers
            4. SCN fix customers should use 26493118

            This has been adeed:
            ==> Note: For 26493118, you will get a message that “This Patchset has been Superseded. Reason: Patch 26925212 is a super set of patch 26493118″, however for this particular fix you need to use 26493118 only. So please ignore this message and use 26493118.”


          • Mike, thanks again for all your work and support.

            “Patch 26925212 does not include the fix. It was specifically built for MDS customers and cannot be provided to all customers”

            But the fact that an older PSU includes and a fix, and its superseded not, does not make sense…

            I think that the truth is because the single oneoff patch 14121009, which is also needed to fully address the problem, has been released for eight platform for combined use with PSU aka 26493118. But for only two platforms (Linux x86-64 and HP-UX Itanium) for PSU aka 26925212.

            One of them, Linux x86-64, just last monday!

            It seems that Oracle was furiously working to get 14121009 ready for PSU, but it failed.

            And decided to keep with older, where 14121009 was already avaiable to more (probably all) platforms.

          • Luis,

            it may look like that but in fact there are other reasons I can’t comment here.
            Again, sorry for any inconvenience!


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