letizia leo wrote: > and the doubt is the following: how is it possible that -line 144- Xmin > is the current transaction ( i.e. it has created this tuple, it is > holding an exclusive lock on it since it has not committed yet) and > that > -line 149- there is a different (?) transaction that is also locking > the > tuple (HEAP_IS_LOCKED=(HEAP_XMAX_EXCL_LOCK||HEAP_XMAX_SHARED_LOCK) )? > Unless we are missing something, this situation is possible exclusively > in case the XMAX transaction is a subtransaction of XMIN, which can > access the tuple despite the exclusive lock held by XMIN.
Exactly. > This seems correct according to the comment in line 154, which refers > to a "subtransaction". It is correct. > Are we understanding correctly what this code is doing and the related > underlying MVCC mechanisms? Can't say, but that part at least you got right :-) -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
