On 8 August 2018 at 00:47, Andres Freund <and...@anarazel.de> wrote: > 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'm not proposing that sessions running older snapshots can't see that there's a new partition. The code I have uses PartitionIsValid() to test if the partition should be visible to the snapshot. The PartitionDesc will always contain details for all partitions stored in pg_partition whether they're valid to the current snapshot or not. I did it this way as there's no way to invalidate the relcache based on a point in transaction, only a point in time. I'm open to better ideas, of course. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
