On Tue, Jun 28, 2011 at 1:47 PM, Kevin Grittner <kevin.gritt...@wicourts.gov> wrote: > (5) When a heap scan is executed, there is no index gap to lock to > cover the predicate involved, so we need to acquire a heap relation > lock -- any insert to the relation by an overlapping transaction is a > rw-conflict. While these *look* just like tuple locks which got > promoted, their purpose is entirely different. Like index locks, > they are for detecting inserts into the "gaps". [Light bulb goes on > over head: in some future release, perhaps it would be worth > differentiating between the two uses of heap relation locks, to > reduce the frequency of false positives. A couple bit flags in the > lock structure might do it.]
You know, it just occurred to me while reading this email that you're using the term "predicate lock" in a way that is totally different from what I learned in school. What I was taught is that the word "predicate" in "predicate lock" is like the word "tuple" in "tuple lock" or the word "relation" in "relation lock" - that is, it describes *the thing being locked*. In other words, you are essentially doing: LOCK TABLE foo WHERE i = 1; I think that what you're calling the predicate lock manager should really be called the siread lock manager, and all of the places where you are "predicate locking" a tuple should really be "siread locking" the tuple. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
