Re: [HACKERS] hash index on unlogged tables doesn't behave as expected

On Tue, Jul 18, 2017 at 4:18 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> Thanks.  Do you have any suggestion for back-branches?  As of now, it
> fails badly with below kind of error:
>
> test=> SELECT * FROM t_u_hash;
> ERROR:  could not open file "base/16384/16392": No such file or directory
>
> It is explained in another thread [3] where it has been found that the
> reason for such an error is that hash indexes are not WAL logged prior
> to 10.  Now, we can claim that we don't recommend hash indexes to be
> used prior to 10 in production, so such an error is okay even if there
> is no crash has happened in the system.

There are a couple of approaches:
1) Marking such indexes as invalid at recovery and log information
about the switch done.
2) Error at creation of hash indexes on unlogged tables.
3) Leave it as-is, because there is already a WARNING at creation.
I don't mind seeing 3) per the amount of work done lately to support
WAL on hash indexes.
-- 
Michael