On Wed, May 15, 2013 at 08:12:34AM +0900, Michael Paquier wrote: > The concept of clause parallelism for backend worker is close to the > concept of clause shippability introduced in Postgres-XC. In the case of > XC, the equivalent of the master backend is a backend located on a node > called Coordinator that merges and organizes results fetched in parallel > from remote nodes where data scans occur (on nodes called Datanodes). The > backends used for tuple scans across Datanodes share the same data > visibility as they use the same snapshot and transaction ID as the backend > on Coordinator. This is different from the parallelism as there is no idea > of snapshot import to worker backends.
Worker backends would indeed share snapshot and XID. > However, the code in XC planner used for clause shippability evaluation is > definitely worth looking at just considering the many similarities it > shares with parallelism when evaluating if a given clause can be executed > on a worker backend or not. It would be a waste to implement twice the same > thing is there is code already available. Agreed. Local parallel query is very similar to distributed query; the specific IPC cost multipliers differ, but that's about it. I hope we can benefit from XC's experience in this area. -- Noah Misch EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
