Re: Design for In-Core Logical Replication
| От | Simon Riggs |
|---|---|
| Тема | Re: Design for In-Core Logical Replication |
| Дата | |
| Msg-id | CANP8+jLBJ+7+5E4LyKo-AXTQaxc8c+xmPoT+WJmE=R9PwzM9ow@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Design for In-Core Logical Replication ("Joshua D. Drake" <jd@commandprompt.com>) |
| Ответы |
Re: Design for In-Core Logical Replication
(Petr Jelinek <petr@2ndquadrant.com>)
|
| Список | pgsql-hackers |
On 20 July 2016 at 16:39, Joshua D. Drake <jd@commandprompt.com> wrote:
--
Logical Replication is a method of replicating data objects and their
changes, based upon their Primary Keys (or Replication Identity). We
Do we want a limitation based on Primary Key, or would it be possible to use just UNIQUE or is that covered under Replication Identity?
That is covered by replication identity.
<para>
Logical Replication uses a Publish and Subscribe model with one or
more Subscribers subscribing to one or more Publications on a
Provider node. Subscribers pull data from the Publications they
subscribe to and may subsequently re-publish data to allow
cascading replication or more complex configurations.
Is that somehow different than Origin/Subscriber or Master/Slave? If not, why are we using yet more terms?
Thanks for asking, an important question that we have a chance to get right before we go too far down the road of implementation.
Issue: We need a noun for CREATE "SOMETHING" (or pg_create_$NOUN). So what noun to use? SQLStandard gives us no guidance here.
I'll explain my thinking, so we can discuss the terms I've recommended, which can be summarized as:
A Provider node has one or more Databases, each of which can publish its data in zero, one or more PUBLICATIONs. A Subscribing node can receive data in the form of zero, one or more SUBSCRIBERs, where each SUBSCRIBER may bring together data from one or more PUBLICATIONs
Here's why...
Master/Slave is not appropriate, since both sending and receiving nodes are Masters.
Origin/Subscriber is used by Slony. The term "Replication Origin" is already used in PG9.5 for something related, but not identical.
Provider/Subscriber is used by Londiste.
Bucardo seems to use Master/Slave according to FAQ.
The Noun we are discussing is something that a single Database can have >1 of, so those terms aren't quite appropriate.
pglogical uses Provider/Subscriber and Replication Sets, so I started with the thought that we might want CREATE REPLICATION SET or pg_create_replication_set(). After some time considering this, ISTM that the term "replication set" may not be that useful since we foresee a future where data is actually filtered and transformed and the feature set extends well beyond what we have with Slony, so I began looking for a term that was general and obvious (POLA).
After some thought, I realised that we are describing this as "Publish & Subscribe", so it makes a lot of sense to just use the terms Publication & Subscription. Those phrases are commonly used by SQLServer, Sybase, Oracle, Redis, RabbitMQ etc which is a pretty big set.
It's also a commonly used Enterprise Integration Design pattern https://en.wikipedia.org/wiki/Publish–subscribe_pattern
I note especially that Publish/Subscribe does not imply any particular topology (a mistake I made earlier when I called this stuff BDR, which confused everybody when we tried to talk about a subset of that functionality called UDR).
So that brings us to...
A Provider node has one or more Databases, each of which can publish its data in zero, one or more PUBLICATIONs. A Subscribing node can receive data in the form of zero, one or more SUBSCRIBERs, where each SUBSCRIBER may bring together data from one or more PUBLICATIONs.
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
В списке pgsql-hackers по дате отправления: