On 01/26/2016 10:43 AM, Craig Ringer wrote:
On 23 January 2016 at 11:17, Steve Singer <st...@ssinger.info <mailto:st...@ssinger.info>> wrote:

    ** Schema changes involving rewriting big tables

    Sometimes you have a DDL change on a large table that will involve
    a table rewrite and the best way of deploying the change is to
    make the DDL change
    on a replicate then once it is finished promote the replica to the
    origin in some controlled fashion.  This avoids having to lock the
    table on the origin for hours.

    pglogical seems to allow minor schema changes on the replica such
    as changing a type but it doesn't seem to allow a DO INSTEAD
    trigger on the replica.  I don't think pglogical currently meets
    this use case particularly well

I'm not sure I fully understand that one.

Say you have a table A with column b

and the next version of your application you want to create a second table B that has column B

create table B (b text);
insert into B select b from a;
alter table a drop column b;

but you want to do this on a replica because it is a very big table and you want to minimize downtown.

You could have a trigger on the replica that performed updates on B.b instead of A except triggers don't seem to get run on the replica.

 Craig Ringer http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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