From: | Craig Ringer <craig(at)2ndquadrant(dot)com> |
---|---|
To: | "Maeldron T(dot)" <maeldron(at)gmail(dot)com> |
Cc: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: logical replication read-only slave |
Date: | 2017-06-16 01:29:38 |
Message-ID: | CAMsr+YGBz_0Ff3Z4F9u2MaONK3Wn00CruB5XBfQefj-CLmn57Q@mail.gmail.com |
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Lists: | pgsql-hackers |
On 15 June 2017 at 23:12, Maeldron T. <maeldron(at)gmail(dot)com> wrote:
> I could send an explicit command for each session to make it read-only
> I could use a read-only role (let’s ignore now I don’t use rules)
You can also set the GUC default_transaction_read_only = on.
But apps can easily clobber that with explicit read/write begin.
Setting it in combination with a role that doesn't have any write
permissions would be sufficient for most practical situations IMO.
> The DDL could be applied in a specific session as whitelisting is safer than
> blacklisting. I think the only missing part is if the subscription could
> turn on the writes for itself.
>
> If you think this would make sense, please consider it.
BDR has the option of marking a node as read-only, which is
implemented using an ExecutorStart_hook. It probably wouldn't be
overly hard to do the same thing as a standalone extension. You'd want
to detect when you were running within a logical replication apply
worker and permit changes then, but I don't expect that'd be unduly
hard.
It'd be nice to have a built-in way to do this, so maybe you could
pursue that for postgresql 11, raising a firm design idea here and
following up with a patch if you get a reasonable approximation of
consensus.
--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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