RE: Block Identifiers in Multitenant Databases

If you used a formatted cdb_extents query for a single object and automated the compare with the mutually sorted and formatted output of od on the file(s)-blocks that could tend to validate your supposition or at least fail to find a contrary example.  

I want to be sure I understand the question: you’re being handed a block without concurrent access to the database and need to identify the root container row block address.  

I wonder whether that’s a trade secret (sarcasm) or whether an Oracle lurker can verify the details. My search fu is too lazy for a comprehensive search at the moment. We’re not missing something obvious like did they add that to concepts or something? (It should be there, right?)  

mwf      

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Jonathan Lewis Sent: Wednesday, October 06, 2021 1:16 PM To: Oracle L; Seth Miller
Subject: Re: Block Identifiers in Multitenant Databases    

Thinking about it a bit, the individual blocks are unlikely to hold any information about their tablespace or absolute file number, otherwise

1. for tablespace number - every block would have to be updated to avoid a collision when you did a 'transport tablespace'
2. for absolute file number - every block would have to be updated when you unplugged a PDB and plugged it in somewhere else.

Regards

Jonathan Lewis    

On Wed, 6 Oct 2021 at 16:55, Seth Miller <sethmiller.sm_at_gmail.com> wrote:

Yes, I noticed this as well and it is pretty easy to identify the file as a whole. Unfortunately, I am dealing with individual blocks. Specifically, I need to identify each block that comes through an rman stream which means I can have blocks from multiple datafiles in a single stream.  

Seth  

On Wed, Oct 6, 2021 at 10:37 AM Jonathan Lewis <jlewisoracle_at_gmail.com> wrote:

Sorry,

I didn't intend my previous reply to go to the individual rather than the group.  

I've just done

od -o {filename} | head -64 on the system tablespace file for the root, seed and pdb of a multi tenant database.

Then I've flagged each line of the file (changed the first space in each line to a letter surrounded by spaces).

The sorted the three files together.  

In v$datafile root system is file 1, seed system is file 5, and the pdb system is file 11.

The following may be a coincidence (the first 6 digit number is the byte number in the file, in Octal:  

0020060 p 020000 000000 000011 000003 000000 000000 000000 000000               prod    system = file# 9
0020060 r 020000 000000 000001 000003 000000 000000 000000 000000               root    system = file# 1
0020060 s 020000 000000 000005 000003 000000 000000 000000 000000               Seed    system = file# 5

 

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