On 2024-Nov-19, Alvaro Herrera wrote: > Hmm, yeah, it seems you're correct about this being an oversight -- we > don't necessarily use a multixact if all we want to do is to store a FOR > SHARE lock.
The "Infomask Bits" section explains correctly. I propose the following amendment, diff --git a/src/backend/access/heap/README.tuplock b/src/backend/access/heap/README.tuplock index 31c52ad28f9..843c2e58f92 100644 --- a/src/backend/access/heap/README.tuplock +++ b/src/backend/access/heap/README.tuplock @@ -70,13 +70,8 @@ KEY SHARE conflict 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 infomask bits specifying the locking strength. There is one exception -here: since infomask space is limited, we do not provide a separate 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.) +setting infomask bits specifying the locking strength. See "Infomask Bits" +below for details on the bit patterns we use. MultiXacts ---------- -- Álvaro Herrera Breisgau, Deutschland — https://www.EnterpriseDB.com/ "Ellos andaban todos desnudos como su madre los parió, y también las mujeres, aunque no vi más que una, harto moza, y todos los que yo vi eran todos mancebos, que ninguno vi de edad de más de XXX años" (Cristóbal Colón)
