Florence Cousin wrote: > Le mardi 15 juin 2010 22:04:06, Bruce Momjian a ?crit : > > > > Wow, that is a confusing double-negative sentence. I have updated the > > text to be: > > > > In addition, rows that satisfied the query conditions as of the > > query snapshot will be locked, although they will not be returned > > if they were updated after the snapshot and no longer satisfy the > > query conditions. > > > > What it is saying is that SELECT FOR UPDATE will lock all rows that > > match the SELECT query using the current snapshot, but the returned rows > > might be different because the rows were changed after the snapshot was > > taken, and a SELECT FOR UPDATE will return the rows as UPDATE will see > > them, which might not match the SELECT snapshot. Yeah, it is confusing. > > Thank you for the patch and the explanation. It is clear for me now (the rows > returned are those that would be returned by an UPDATE, that is pretty > logical). > > But I think most of the users will still not understand this, because they do > not know what a snapshot is, and do not really know how locking works. > > And I managed to understand thank to the explanation, but I think I could not > understand with the new version of the explanation alone (the fact that rows > returned are the rows as UPDATE will see them) > > Maybe it would be clearer with a longer explanation, or a link to an > explanation?
Well, the entire area is very complicated, but do we want to add even more text there? I am not sure. -- Bruce Momjian <[email protected]> http://momjian.us EnterpriseDB http://enterprisedb.com + None of us is going to be here forever. + -- Sent via pgsql-docs mailing list ([email protected]) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-docs
