Tasks for ZDLRA are the pillar of how the backups are processed, everything is one task. So, when you ingest incremental backup one task is created but can occur that it get a freeze at ORDERING_WAIT state. These tasks are hard to identify and can create a big problem for your virtual full backup and backup strategy. Below I will show how they occur and how to solve the problem.
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).
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.
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.
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.
ZDLRA tables are owned by rasys user and are one extension of rman recovery catalog views. The internal tables that were added are just a few, but are important to understand how tasks works (mainly INDEX_BACKUP). In this post, I will show tables like plans, plans_details, blocks, and chunks. And besides that, show a little glimpse about how the files are stored.
If you check, officially, the rman recovery catalog already includes some columns from ZDLRA, the column VB_KEY identify the virtual backup key inside ZDLRA. It exists in RC_BACKUP_PIECE as an example. The extra tables added are linked with SBT tasks (clone to tape or cloud), replication (to other ZDLRA), storage (chunks), vbdf and plans (virtual full backup).