On Wed, May 15, 2013 at 08:49:00PM +0200, Andres Freund wrote: > On 2013-05-13 10:28:59 -0400, Noah Misch wrote: > > Each worker needs to make SnapshotNow visibility decisions coherent with the > > master. For sorting, this allows us to look up comparison functions, even > > when the current transaction created or modified those functions. This will > > also be an essential building block for any parallelism project that > > consults > > user tables. Implementing this means copying the subtransaction stack and > > the > > combocid hash to each worker. For the sake of completeness, we should also > > copy the global MVCC snapshot data (sorting probably won't care). It also > > means forbidding, while a parallel task is in flight, operations that affect > > the transaction state: > > Btw, if you assume you can simply copy a snapshot from the normal > backend to the worker backend to make visibility decisions in the > general case: You're wrong. Unfortunately you need in-memory state to > make sense of combocids...
Correct. If you think of any required state information that I did not list above, please let me know. -- 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
