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How one node became master for database blocks
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Message Score Author Date
Dear all, Just assume. I have <b> 3 node </b...... Jill Salalila Oct 17, 2018, 16:30
First based on an internal algorithm on block id...... Michel Cadot Oct 17, 2018, 17:06
Hi Mike, I am beginner on RAC. I want to under...... Jill Salalila Oct 17, 2018, 17:15
At the beginning, the block are owned depending ...... Score: 200 PtsScore: 200 PtsScore: 200 PtsScore: 200 PtsScore: 200 Pts Michel Cadot Oct 17, 2018, 18:38
To answer your question (byt I don't know what y...... Score: 100 PtsScore: 100 PtsScore: 100 PtsScore: 100 PtsScore: 100 Pts Michel Cadot Oct 17, 2018, 19:45
Hi Mike, As per your explanation, Whenever we b...... Jill Salalila Oct 18, 2018, 06:30
At boot time there is no query, so no informatio...... Michel Cadot Oct 18, 2018, 08:05
Hi Mike Thanks for all response. Are you compl...... Jill Salalila Oct 18, 2018, 08:29
What SELECT are you talking about? Regards M...... Michel Cadot Oct 18, 2018, 09:00
Select * from scott.emp; This select query br...... Jill Salalila Oct 18, 2018, 14:00
As I said, at startup you have no query. "sel...... Michel Cadot Oct 18, 2018, 16:58
From my tests, it seems that, in the latest vers...... Score: 100 PtsScore: 100 PtsScore: 100 PtsScore: 100 PtsScore: 100 Pts Michel Cadot Oct 18, 2018, 18:23

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Subject: How one node became master for database blocks
Author: Jill Salalila, Philippines
Date: Oct 17, 2018, 16:30, 363 days ago
Os info: Oracle Linux 6.7
Oracle info: 12.1.0.2
Message: Dear all,

Just assume.

I have 3 node RAC.
On What basis, a node can become master of the blocks ?

Only based on SELECT QUERY or anything else ?

Suppose my Database have 9 crore blocks.

Are they distributed evenly among 3 nodes ?
Each node has master for 3 crore blocks.

3 + 3 + 3 = 9 ?

Please update
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Subject: Re: How one node became master for database blocks
Author: Michel Cadot, France
Date: Oct 17, 2018, 17:06, 363 days ago
Message:
First based on an internal algorithm on block id.

Regards
Michel
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Subject: Re: How one node became master for database blocks
Author: Jill Salalila, Philippines
Date: Oct 17, 2018, 17:15, 363 days ago
Message: Hi Mike,

I am beginner on RAC.
I want to understand it clearly.

My Straight Question

Suppose my Database have 9 crore blocks.

Are they distributed evenly among 3 nodes when i boot the Server ?
Each node has master for 3 crore blocks.

Thanks Mike
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Subject: Re: How one node became master for database blocks
Author: Michel Cadot, France
Date: Oct 17, 2018, 18:38, 363 days ago
Score:   Score: 200 PtsScore: 200 PtsScore: 200 PtsScore: 200 PtsScore: 200 Pts
Message:
At the beginning, the block are owned depending on an Oracle internal algorithm based on many things like SGA sizes and can change at any time and you can't know it for sure.

Then, the owner of a block is the last instance that acquired it for write access.

Regards
Michel
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Subject: Re: How one node became master for database blocks
Author: Michel Cadot, France
Date: Oct 17, 2018, 19:45, 363 days ago
Score:   Score: 100 PtsScore: 100 PtsScore: 100 PtsScore: 100 PtsScore: 100 Pts
Message:
To answer your question (byt I don't know what you can do with it): at startup, for each object, Oracle gives the master role to node 1 for a first chunk of blocks, then to node 2 for the second chunk, then to node 3 for the third chunk and so on.

Chunk size is determined by "_lm_contiguous_res_count" parameter (128 by default).

Regards
Michel
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Subject: Re: How one node became master for database blocks
Author: Jill Salalila, Philippines
Date: Oct 18, 2018, 06:30, 362 days ago
Message: Hi Mike,

As per your explanation, Whenever we boot our machine,
based on SGA size,

Each and Every objects blocks are distributed among the nodes. and NOT based on SELECT QUERY





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Subject: Re: How one node became master for database blocks
Author: Michel Cadot, France
Date: Oct 18, 2018, 08:05, 362 days ago
Message:
At boot time there is no query, so no information about usage.
And as I said, the algorithm may (and will) change with the versions.
Maybe Oracle will store somewhere information about object usages (it does it in memory during instance life so why not storing it from time to time like ASH data) and use this information at startup (and maybe it already does it but this is not documented as is not documented the (simplified) algorithm I gave in my previous post).
For the moment, from what I know, the blocks are evenly mastered across the nodes (but what happens when an instance starts or shuts down, how blocks are remastered?).

Anyway, the purpose of Oracle is to try to get an algorithm for the best performances (which is a never ending task) and so if I know this one what can I do with it? (More how can I verify the algorithm I know is actually the one that is used?)

Regards
Michel
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Subject: Re: How one node became master for database blocks
Author: Jill Salalila, Philippines
Date: Oct 18, 2018, 08:29, 362 days ago
Message: Hi Mike

Thanks for all response.
Are you completely or partially denying SELECT Query option?

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Subject: Re: How one node became master for database blocks
Author: Michel Cadot, France
Date: Oct 18, 2018, 09:00, 362 days ago
Message:
What SELECT are you talking about?

Regards
Michel
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Subject: Re: How one node became master for database blocks
Author: Jill Salalila, Philippines
Date: Oct 18, 2018, 14:00, 362 days ago
Message:
Select * from scott.emp;

This select query brings some blocks to the SGA.
So that current node become master of all blocks associated to scott.emp table

Thanks
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Subject: Re: How one node became master for database blocks
Author: Michel Cadot, France
Date: Oct 18, 2018, 16:58, 362 days ago
Message:
As I said, at startup you have no query.

"select * from scott.emp;" may come AFTER startup.

AFTER startup, no SELECT query changes the master of the blocks (at least in the versions I tested and this may, of course, change with versions so you have to test in your own version and test again each time you change the version, including each patchset -- and maybe other parameters).

Regards
Michel
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Subject: Re: How one node became master for database blocks
Author: Michel Cadot, France
Date: Oct 18, 2018, 18:23, 362 days ago
Score:   Score: 100 PtsScore: 100 PtsScore: 100 PtsScore: 100 PtsScore: 100 Pts
Message:
From my tests, it seems that, in the latest versions, blocks can be "remastered" in an other instance where they are mostly accessed there.
A lack of access to RAC environment prevent me from giving more details.

Regards
Michel
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