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List:       postgresql-general
Subject:    Re: [External] Re: wal_level logical for streaming replication
From:       Vijaykumar Jain <vjain () opentable ! com>
Date:       2019-08-29 10:56:40
Message-ID: CAE7uO5iCxXOKZPT+TYRpv5o1b=P_4UvZanRd4ZoNdiTvcscv6g () mail ! gmail ! com
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Thanks Laurenz,


Regards,
Vijay


On Thu, Aug 29, 2019 at 2:07 AM Laurenz Albe <laurenz.albe@cybertec.at> wrote:
>
> On Wed, 2019-08-28 at 21:44 +0530, Vijaykumar Jain wrote:
> > If I change wal_level back to replica, will it corrupt wal? coz it
> > will then be having diff information ( r format of data ?)
>
> That's why you have to restart the server when you change that
> parameter.  This way, there will be a checkpoint marking the change.
>
> > What is the base reason as to why ddls are not sent via logical
> > replication but the hot standby has ddl changes reflected absolutely
> > fine ?
>
> Physical streaming replication just replicates the database files,
> so it also replicates DDL statements, which are just changes to the
> catalog tables.
>
> Basically, anything that can be recovered can be replicated.
>
> Logical replication has to perform "logical decoding", that is,
> it has to translate the (physical) WAL information into logical
> information (waht row was modified in which table).
>
> So this is much more complicated.  It should be possible in theory,
> but nobody has got around to solving the difficulties involved yet.
>
> > and there is one large limitation on large object support for logical
> > replication?
> > Where can I see the limitation on size or is it just certain data
> > types ?
>
> This has nothing to do with the size; I guess the answer is the same as
> above.  One proble that I can see immediately is that primary and
> standby don't share the same OIDs, yet every large object is identified
> by its OID.  So I think this is a fundamental problem that cannot be
> solved.
>
> Yours,
> Laurenz Albe
> --
> Cybertec | https://www.cybertec-postgresql.com
>


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