| From: | Zheng Li <zhengli10(at)gmail(dot)com> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Cc: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Euler Taveira <euler(at)eulerto(dot)com>, "Kumar, Sachin" <ssetiya(at)amazon(dot)com>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>, "Jonathan S(dot) Katz" <jkatz(at)postgresql(dot)org> |
| Subject: | Re: Initial Schema Sync for Logical Replication |
| Date: | 2023-03-22 18:04:15 |
| Message-ID: | CAAD30U+xPadJCyZzgg9fe4FCzFVOW=DQBmAc03_zy5BrnRRkSg@mail.gmail.com |
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| Lists: | pgsql-hackers |
> > Yes. Do we have any concrete use case where the subscriber is an older
> > version, in the first place?
> >
>
> As per my understanding, it is mostly due to the reason that it can
> work today. Today, during an off-list discussion with Jonathan on this
> point, he pointed me to a similar incompatibility in MySQL
> replication. See the "SQL incompatibilities" section in doc[1]. Also,
> please note that this applies not only to initial sync but also to
> schema sync during replication. I don't think it would be feasible to
> keep such cross-version compatibility for DDL replication.
I think it's possible to make DDL replication cross-version
compatible, by making the DDL deparser version-aware: the deparsed
JSON blob can have a PG version in it, and the destination server can
process the versioned JSON blob by transforming anything incompatible
according to the original version and its own version.
Regards,
Zane
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