Re: ATTACH/DETACH PARTITION CONCURRENTLY

On 7 August 2018 at 13:47, Andres Freund <andres@anarazel.de> wrote:
> Hi,
>
> On 2018-08-08 00:40:12 +1200, David Rowley wrote:
>> 1. Obtain a ShareUpdateExclusiveLock on the partitioned table rather
>> than an AccessExclusiveLock.
>> 2. Do all the normal partition attach partition validation.
>> 3. Insert pg_partition record with partvalid = true.
>> 4. Invalidate relcache entry for the partitioned table
>> 5. Any loops over a partitioned table's PartitionDesc must check
>> PartitionIsValid(). This will return true if the current snapshot
>> should see the partition or not. The partition is valid if partisvalid
>> = true and the xmin precedes or is equal to the current snapshot.
>
> How does this protect against other sessions actively using the relcache
> entry? Currently it is *NOT* safe to receive invalidations for
> e.g. partitioning contents afaics.

I think you may be right in the general case, but ISTM possible to
invalidate/refresh just the list of partitions.

If so, that idea would seem to require some new, as-yet not invented mechanism.

-- 
Simon Riggs                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services