Tag Archives: Database


My first post of 2021 is just Thank You. Thanks for reading my posts and following me on my social media (Twitter/LinkedIn/Blog). Thanks for all of the 41.000 site access during the last year and for all that attended my sessions at the online events. I hope that was possible to help you with something about Oracle.

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DB_UNIQUE_NAME, PDB, and Data Guard

When you change the parameters for the database is possible to specify the db_unique_name and allow more control where you want to apply/use it. This is very useful to limit the scope, but you need to be aware of some collateral effects. Even not present at the official doc, you can use it. But check here some details that you need to take care of.

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Exadata, Missing Metric

Understand metrics for Exadata Storage Server is important to understand how all the software features are being used and all the details from that. Here I will discuss one case where the FC_IO_BY_R_SEC metric can show not precise values. And I will discuss one missing metric that can save a lot.

If you have doubts about metrics, you can check my post about metrics, it was an introduction, but cover some aspects of how to read and use it. You can check my other post where I show how to use metric DB_FC_IO_BY_SEC to identify database problems that can be hidden when checking only from the database side.

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Exadata, Understanding Metrics

Metrics for Exadata deliver to you one way to deeply see, and understand, what it is happening for Exadata Storage Server and Exadata Software. Understand it is fundamental to identify and solve problems that can be hidden (or even unsee) from the database side. In this post, I will explain details about these metrics and what you can do using them.

My last article about Exadata Storage Server metrics was about one example of how to use them to identify problems that do not appear in the database side. In that post, I showed how I used the metric DB_FC_IO_BY_SEC to identify bad queries.

The point for Exadata (that I made in that article), is that most of the time, Exadata is so powerful that bad statements are handled without a problem because of the features that exist (flashcache, smartio, and others). But another point is that usually, Exadata is a high consolidated environment, where you “consolidate” a lot of databases and it is normal that some of them have different workloads and needs. Using metrics can help you to do a fine tune of your environment, but besides that, it delivers to you one way to check and control everything that’s happening.

In this post, I will not explain each metric one by one, but guide you to understand metrics and some interesting and important details about them.

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ZDLRA, Multi-site protection – ZERO RPO for Primary and Standby

ZDLRA can be used from a small single database environment to big environments where you need protection in more than one site at the same time. At every level, you can use different features of ZDLRA to provide desirable protection. Here I will show how to reach zero RPO for both primary and standby databases. All the steps, doc, and tech parts are covered.

You can check the examples the reference for every scenario int these two papers from the Oracle MAA team: MAA Overview On-Premises and Oracle MAA Reference Architectures. They provide good information on how to prepare to reduce RPO and improve RTO. In resume, the focus is the same, reduce the downtime and data loss in case of a catastrophe (zero RPO, and zero RPO).

Multi-site protection

If you looked both papers before, you saw that to provide good protection is desirable to have an additional site to, at least, send the backups. And if you go higher, for GOLD and PLATINUM environments, you start to have multiple sites synced with data guard. These Critical/Mission-critical environments need to be protected for every kind of catastrophic failure, from disk until complete site outage (some need to follow specific law’s requirements, bank as an example).

And the focus of this post is these big environments. I will show you how to use ZDLRA to protect both sites, reaching zero RPO even for standby databases. And doing that, you can survive for a catastrophic outage (like entire datacenter failure) and still have zero RPO. Going further, you can even have zero RPO if you lose completely on site when using real-time redo for ZDLRA, and this is not written in the docs by the way.

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ZDLRA, Real-Time Redo and Zero RPO

The idea for Real-Time Redo is to reach zero RPO for every kind of database and this includes ones with and without DG. As you can see in my last post, where I showed how to configure Real-Time Redo for one database, some little steps need to be executed and they are pretty similar than a remote destination for archivelog for DG.

But if you noticed, the configuration for the remote destination was defined as ASYNC, and hinted like that at ZDLRA docs (“Protection of Ongoing Transactions” or at “How Real-Time Redo Transport Works”). In the same post, I suggested as “controversial” because the ASYNC does not guarantee the RPO zero. 

You can see more in the DataGuard docs at (Oracle Data Guard Protection Modes and Oracle Data Guard Concepts and Administration), but the resume it is:

  • ASYNC: The primary database does not wait for the response from a remote destination.
  • SYNC/NOAFIRM: The Primary database holds commit until the remote destination report that received the redo data. It does not wait until the remote site report that wrote the data in the disc.
  • SYNC/AFFIRM: The primary database holds commit until the remote destination report that received redo data and wrote it at the disk.

You can read with more details the difference here: Best Practices for Synchronous Redo Transport and Best Practices for Asynchronous Redo Transport.

The idea is simple, if you use ASYNC, there is no guarantee for zero data loss between the primary database and the remote destination.

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ZDLRA Internals, Virtual Full Backup

Virtual Full Backup probably is the most know feature of Oracle Zero Data Loss Recovery Appliance (ZDLRA) and you can check here how it works. In this post I will show how virtual full backup works internally and integrate INDEX_BACKUP task with tables like PLANS, PLAN_DETAILS, CHUNKS, and BLOCKS.

About the internal tables, you can check my previous post “ZDLRA Internals, Tables and Storage” where I explained details about that. To understand the INDEX_BACKUP task, check my post “ZDLRA Internals, INDEX_BACKUP task in details”. But if you know nothing and want to start reading about ZDLRA, you can check my post “Understanding ZDLRA” and check all the features and details.

The base for this article is virtual full backup and incremental forever strategy. I explained both at “ZDLRA, Virtual Full Backup and Incremental Forever” and I included hot it’s work integrated with rman backup. Basically, after an initial backup level 0, you execute just level 1 backups and ZDLRA generated a virtual backup level 0. But here, in this post, I will show you how it works in some internal details.

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ZDLRA, 19.2

Last week, at 27/August/2019, ZDLRA team released the new major version 19.2 ( of Recovery Appliance Software. As always, some new features like supported databases, but some downsides too.

The main features for the software side:

  • Support for 19c databases.
  • Improved way to apply the patch (the rpm installation is not anymore manual).
  • Improved way to rollback the patch in some cases.

Other changes that deserve the hint:

  • Runs over 19.4 version of GRID and RDBMS.
  • Runs over Exadata System Software (this means OEL 7) for DB and Storage.
  • Updated version for TFA, Exachk, and OEDA; all 19.x version.

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ZDLRA Internals, INDEX_BACKUP task in details

For ZDLRA, the task type INDEX_BACKUP it is important (if it is not the most) because it is responsible to create the virtual full backup. This task runs for every backup that you ingest at ZDLRA and here, I will show with more details what occurs at ZDLRA: internals steps, phases, and tables involved.

I recommend that you check my previous post about ZDLRA: ZDLRA Internals, Tables and Storage, ZDLRA, Virtual Full Backup and Incremental Forever, and Understanding ZDLRA. They provide a good base to understand some aspects of ZDLRA architecture and features.


As you saw in my previous post, ZDLRA opens every backup that you sent and read every block of it to generate one new virtual full backup. And this backup is validated block a block (physically and logically) against corruption. It differs from a snapshot because it is content-aware (in this case it is proprietary Oracle datafile blocks inside another proprietary Oracle rman block) and Oracle it is the only that can do this guaranteeing that result is valid.

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How to use ZDLRA and enroll a database

ZDLRA it is an Oracle dedicate appliance specialized to manage your backups, but more than that, provide you zero data loss. I already made an introduction about ZDLRA in my previous post and here I will show how to use and enrolling protected database at ZDLRA: enroll database, create policies and access with rman. Understand how to use ZDLRA, at least the starting point.

Every project starts with scope definition, steps, and requirements. It is not different for ZDLRA project, it is a big appliance, expensive, and integrate a lot of things in just one place: backups, archivelogs, redo, replication, and RPO. The requirements vary from project to project, I will not discuss that here. But will show you the tech part about the usage.

The post has two divisions, the first it is the technical part. You can check how to do that. The second contains the information/documentation part, where I will show more details about the steps.