| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Craig Ringer <craig(at)2ndquadrant(dot)com> |
| Cc: | obartunov(at)gmail(dot)com, Bruce Momjian <bruce(at)momjian(dot)us>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, Petr Jelinek <petr(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: pglogical - logical replication contrib module |
| Date: | 2016-02-17 08:27:50 |
| Message-ID: | 20160217082749.GI25464@awork2.anarazel.de |
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| Lists: | pgsql-hackers |
On 2016-02-17 09:33:56 +0800, Craig Ringer wrote:
> Some DDL operations don't translate well to a series of replicatable
> actions. The case I hit the most is
>
> ALTER TABLE mytable ADD COLUMN somecolumn sometype NOT NULL DEFAULT
> some_function();
>
> This is executed (simplified) by taking an ACCESS EXCLUSIVE lock, changing
> the catalogs but not making the changes visible yet, rewriting the table,
> and committing to make the rewritten table and the catalog changes visible.
>
> That won't work well with logical replication.
FWIW, I think this is much less a fundamental, and more an
implementation issue. Falling back to just re-replicating the table, and
then optimizing a few common cases (only immutable DEFALUT/USING
involved) should be enough for a while.
Lets get the basics right, before reaching for the moon.
Greetings,
Andres Freund
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