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Subject: Re: logical decoding of two-phase transactions
From: Stas Kelvich <s.kelvich@postgrespro.ru>
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Date: Thu, 5 Jan 2017 15:43:04 +0300
Cc: PostgreSQL mailing lists <pgsql-hackers@postgresql.org>,
 Craig Ringer <craig@2ndquadrant.com>
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To: Simon Riggs <simon@2ndquadrant.com>
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> On 5 Jan 2017, at 13:49, Simon Riggs <simon@2ndquadrant.com> wrote:
>=20
> Surely in this case the master server is acting as the Transaction
> Manager, and it knows the mapping, so we are good?
>=20
> I guess if you are using >2 nodes then you need to use full 2PC on each n=
ode.
>=20
> Please explain precisely how you expect to use this, to check that GID
> is required.
>=20

For example if we are using logical replication just for failover/HA and al=
lowing user
to be transaction manager itself. Then suppose that user prepared tx on ser=
ver A and server A
crashed. After that client may want to reconnect to server B and commit/abo=
rt that tx.
But user only have GID that was used during prepare.

> But even then, if you adopt the naming convention that all in-progress
> xacts will be called RepOriginId-EPOCH-XID, so they have a fully
> unique GID on all of the child nodes then we don't need to add the
> GID.

Yes, that=E2=80=99s also possible but seems to be less flexible restricting=
 us to some
specific GID format.

Anyway, I can measure WAL space overhead introduced by the GID=E2=80=99s in=
side commit records
to know exactly what will be the cost of such approach.

--=20
Stas Kelvich
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company


--=20
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