Oracle databases and PMEM

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Anton Gavriliuk

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Sep 14, 2021, 1:10:33 PM9/14/21
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Hi all

I noticed that Oracle 21c supports PMEM DAX access.

For Oracle 21c I/O intensive workloads it should be great!

But, does Oracle support any PMEM solution for 19c ?, any PMEM backports 21c -> 19c ??

Anton

aake...@gmail.com

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Sep 14, 2021, 2:56:25 PM9/14/21
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There is pmem support, but it isn't same. The pmemdb support may not be backported the best I know. Underneath pmemsb is the pmemfs that I authored. I think it is available only from 23, although 21c does have some code that was basis for 23.

Anton Gavriliuk

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Sep 15, 2021, 3:29:32 AM9/15/21
to aake...@gmail.com, pmem
Hello

> There is pmem support, but it isn't same.

Could you clarify please ?
According Oracle 21c documentation, 21c supports DAX access - 


I didn't hear anything about 23.

Back to the 19c.
I assume no DAX access for 19c.  But does Oracle support (or planning to support) pmem in fsdax mode for 19c ?? avoiding potential data loss during torn writes caused by unexpected power loss for example.

Anton

вт, 14 сент. 2021 г. в 21:56, aake...@gmail.com <aake...@gmail.com>:
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aake...@gmail.com

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Sep 20, 2021, 12:59:35 PM9/20/21
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I meant the 19c and 21c are not necessarily same. What is referred to as "pmemdb" in 21, to my best knowledge won't be available in 19c. Also, the code for "pmemdb" is there for 21c, and so is documentation, but some last minute finishing touches for a v1 that went into 23 didn't make it to the cutoff for 21c. 19c will have fsdax, yes. REDO logs, can be (to my knowledge, and I am just one developer) can be created on an XFS (DAX) fs. pmemdb distinguishes itself from this by allowing the buffer cache to allow byte reads directly from datafiles, as long as pmemfs and data file block sizes match. 

Admittedly this is indeed a bit confusing, so the keyword is "pmemdb". The pmemdb link applies to 21c (or  21.3 or 23, when they appear), not to 19c.

Anton Gavriliuk

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Sep 21, 2021, 2:31:58 PM9/21/21
to aake...@gmail.com, pmem
Thank you for the detailed explanation.

> 19c will have fsdax, yes.

That means that is not yet available.  So any plans, when ?

Anton

пн, 20 сент. 2021 г. в 19:59, aake...@gmail.com <aake...@gmail.com>:

aake...@gmail.com

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Sep 24, 2021, 3:27:00 PM9/24/21
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21.3 onwards only. I don't think the feature would be backported. Technically may not be feasible. I believe Dell is testing it, they did hit on a doc bug, but nothing thus far came back to the filestore code as an issue. Not that it won't, of course. 

Anton Gavriliuk

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Sep 24, 2021, 4:27:34 PM9/24/21
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Sorry, but it is a bit confused me.

Previously you said

19c will have fsdax, yes.

Now

21.3 onwards only.

Anton




пт, 24 сент. 2021 г. в 22:27, aake...@gmail.com <aake...@gmail.com>:

aake...@gmail.com

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Sep 28, 2021, 2:00:10 PM9/28/21
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fsdax support and pmemdb are not same thing - they both depend on fsdax. 19c does support fsdax, but will not have pmemdb. pmemdb is more than just fsdax. It allows the buffer cache to read bytes from files as opposed to having to cache blocks in dram from disks. pmemdb is a tighter integration with a dedicated pmemfs (filestore based on fsdax). 19c won't have its buffer cache being cognizant about fsdax as in pmemdb, which is available in 21.3

Hope that clarifies.

-Ankur

Anton Gavriliuk

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Sep 28, 2021, 2:20:12 PM9/28/21
to aake...@gmail.com, pmem
Hi  Ankur

Thank you.  Now it is clear.

> 19c does support fsdax

So when fsdax will be supported for 19c ?  Is it already or when ??

Anton

вт, 28 сент. 2021 г. в 21:00, aake...@gmail.com <aake...@gmail.com>:

aake...@gmail.com

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Sep 28, 2021, 6:04:23 PM9/28/21
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I can only speak for pmemdb. I am not personally involved in other efforts and hence not really qualified to talk about it. I am sure the support or the PMs would be happy to help.

-Ankur

ranjit...@gmail.com

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Oct 10, 2021, 8:56:51 AM10/10/21
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Oracle supports PMEM in 19c via the Oracle Memory Speed File System. Here is a link to the deployment guide. 

Anton Gavriliuk

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Oct 11, 2021, 7:31:12 AM10/11/21
to ranjit...@gmail.com, pmem
Thank you!

Looks pretty good.  I'm going to test it.

The only problem I see - putting the entire Oracle DB on pmem is still quite scary due to no local pmem redundancy.

Remote redundancy provides Oracle Data Guard, but local ??

Mdadm and other software raids will eliminate the "dax" mount option for xfs file system, which must be for the OMS file system. 

We can write redo logs on 2 different pmem file systems simultaneously using Oracle redo multiplexing, but there is nothing for datafiles...

Anton

вс, 10 окт. 2021 г. в 15:56, ranjit...@gmail.com <ranjit...@gmail.com>:
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