On Tue, Mar 06, 2012 at 04:39:32PM -0300, Alvaro Herrera wrote: > Here's a first attempt at a README illustrating this. I intend this to > be placed in src/backend/access/heap/README.tuplock; the first three > paragraphs are stolen from the comment in heap_lock_tuple, so I'd remove > those from there, directing people to this new file instead. Is there > something that you think should be covered more extensively (or at all) > here? ... > > When there is a single locker in a tuple, we can just store the locking info > in the tuple itself. We do this by storing the locker's Xid in XMAX, and > setting hint bits specifying the locking strength. There is one exception > here: since hint bit space is limited, we do not provide a separate hint bit > for SELECT FOR SHARE, so we have to use the extended info in a MultiXact in > that case. (The other cases, SELECT FOR UPDATE and SELECT FOR KEY SHARE, are > presumably more commonly used due to being the standards-mandated locking > mechanism, or heavily used by the RI code, so we want to provide fast paths > for those.)
Are those tuple bits actually "hint" bits? They seem quite a bit more powerful than a "hint". -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
