Re: Online enabling of checksums

Hi,

On 2018-02-22 21:16:02 +0100, Magnus Hagander wrote:
> You could do that, but then you've moving the complexity to managing that
> list in shared memory instead.

Maybe I'm missing something, but how are you going to get quick parallel
processing if you don't have a shmem piece? You can't assign one
database per worker because commonly there's only one database. You
don't want to start/stop a worker for each relation because that'd be
extremely slow for databases with a lot of tables. Without shmem you
can't pass more than an oid to a bgworker. To me the combination of
these things imply that you need some other synchronization mechanism
*anyway*.


> I'm not  sure that's any easier... And
> certainly adding a catalog flag for a usecase like this one is not making
> it easier.

Hm, I imagined you'd need that anyway. Imagine a 10TB database that's
online converted to checksums. I assume you'd not want to reread 9TB if
you crash after processing most of the cluster already?

Regards,

Andres Freund