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From: Andrey V. Lepikhov <a.lepikhov@postgrespro.ru>
To: tsunakawa.takay@fujitsu.com <tsunakawa.takay@fujitsu.com>
To: PostgreSQL-Dev <pgsql-hackers@postgresql.org>
Cc: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: Masahiko Sawada <masahiko.sawada@2ndquadrant.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>
Cc: movead.li@highgo.ca <movead.li@highgo.ca>
Subject: Re: Global snapshots
Date: Fri, 26 Feb 2021 11:20:49 +0500
Message-ID: <a0503174-9ac9-fe2c-1788-1a1337d72453@postgrespro.ru> (raw)
In-Reply-To: <TYAPR01MB2990CAC9CE3D0AA63B45053CFED50@TYAPR01MB2990.jpnprd01.prod.outlook.com>
References: <07b2c899-4ed0-4c87-1327-23c750311248@postgrespro.ru>
	<TYAPR01MB2990E83F9E886A9C8AB8E269FE760@TYAPR01MB2990.jpnprd01.prod.outlook.com>
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	<806c3708-26ea-b94d-87b1-d48e41e93726@postgrespro.ru>
	<TYAPR01MB2990F6F2A75657899A7E3A30FE270@TYAPR01MB2990.jpnprd01.prod.outlook.com>
	<d17da3c0-54bb-6221-7ec7-151f6be39e5f@oss.nttdata.com>
	<TYAPR01MB299093D3F5E8BC2D80D5DFD6FE270@TYAPR01MB2990.jpnprd01.prod.outlook.com>
	<88a2642f-1ce6-a9d2-5d26-1221a2c4e072@oss.nttdata.com>
	<CAA4eK1LMQYtY1kJX5RpxkUCnrFnGqj--zcAGVH7Sp3mcPRRuvg@mail.gmail.com>
	<dc6d5fe2-7bdf-1b3f-1027-e152b979c12f@oss.nttdata.com>
	<CA+fd4k5d9Jjt2zwCFwm9FmFF1m6J1_ixaU_X7noM9qkDWCbAzA@mail.gmail.com>
	<f59e3cf8-84d7-4a2b-218d-48ffac488566@oss.nttdata.com>
	<TYAPR01MB299083299DA94BA849358BEEFE170@TYAPR01MB2990.jpnprd01.prod.outlook.com>
	<TYAPR01MB2990CAC9CE3D0AA63B45053CFED50@TYAPR01MB2990.jpnprd01.prod.outlook.com>

On 1/1/21 8:14 AM, tsunakawa.takay@fujitsu.com wrote:
> --------------------------------------------------
> 11. A method comprising:
> receiving information relating to a distributed database transaction operating on data in data stores associated with respective participating nodes associated with the distributed database transaction;
> requesting commit time votes from the respective participating nodes, the commit time votes reflecting local clock values of the respective participating nodes;
> receiving the commit time votes from the respective participating nodes in response to the requesting;
> computing a global commit timestamp for the distributed database transaction based at least in part on the commit time votes, the global commit timestamp reflecting a maximum value of the commit time votes received from the respective participating nodes; and
> synchronizing commitment of the distributed database transaction at the respective participating nodes to the global commit timestamp,
> wherein at least the computing is performed by a computing device.

Thank you for this analysis of the patent.
After researching in depth, I think this is the real problem.
My idea was that we are not using real clocks, we only use clock ticks 
to measure time intervals. It can also be interpreted as a kind of clock.

That we can do:
1. Use global clocks at the start of transaction.
2. Use CSN-based snapshot as a machinery and create an extension to 
allow user defined commit protocols.

-- 
regards,
Andrey Lepikhov
Postgres Professional





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