On 6/8/2016 12:57 PM, Ben Buckman wrote:
> Hello,
> I would like to rename a table with ~35k rows (on pgsql 9.4), let's say
> from `oldthings` to `newthings`.
> Our application is actively reading from and writing to this table, and
> the code will break if the table name suddenly changes at runtime. So I
> can't simply run an `ALTER TABLE oldthings RENAME TO newthings`, unless
> we take downtime, which we'd prefer not to do. (I'd also prefer to avoid
> a data migration from one table to another, which would require
> dual-writes or some other way to handle data written during the transition.)
>
> It seems that a reasonable approach to do this without downtime, would
> be to use a temporary VIEW. We can `CREATE VIEW newthings AS SELECT *
> FROM oldthings;`. Views in pg9.4 that are backed by a single table
> support writes. So my plan is like this:
>
> 1. Create the view, essentially as an alias to the table.
> 2. In the code, change all references from the old name to the new name.
> The code would "think" it's using a renamed table, but would really be
> using a view.
> (At this point, I expect that all basic CRUD operations on the view
> should behave as if they were on the table, and that the added
> performance impact would be negligible.)
> 3. In a transaction, drop the view and rename the table, so `newthings`
> is now the original table and `oldthings` no longer exists. (In my
> testing, this operation took <10ms.)
> (When this is done, the view will have only existed and been used by
> the application for a few minutes.)
>
> What are people's thoughts on this approach? Is there a flaw or
> potential danger that I should be aware of? Is there a simpler approach
> I should consider instead?
>
> Thank you
>
>
> --
>
>
> Shyp
> *Ben Buckman / Platform Engineering*
> www.shyp.com
> Shipping made easy <https://www.shyp.com/>
>
>
I think it kinda depends on how you roll out an application. Will you
kick everyone out, updated it and let them back in? Sounds like you
want to avoid that to avoid downtime.
But, if your old app is hitting a view, and inserts data via the view
into the new table, will it be good data? Will the new app be ok with it?
-Andy