I wrote a while ago > So pg_subtrans remains the same, and we assign a new Xid to each > subtransaction. Each tuple gets Xmin/Xmax according to the Xid of the > current subtransaction. Within the transaction tree we don't use the > Xid to check for visibility, but Cmin/Cmax and the abort bitmap.
... and meanwhile I forgot why this subthread started: I haven't solved the original problem, which is that I want to avoid enlarging the HeapTupleHeader. But currently there is need for storing both a Cmin and a Xmax :-( Manfred: the code you read adds a single bit to the infomask, which is there basically to be able to say whether the Cmin has been overwritten with a Xmax. So the assumption was that when we see that this has happenned, the Cmin is no longer important (== every future command can already see the tuple), and we have to check the Xmax in pg_clog to see if the deleting subtransaction has aborted (in which case the tuple is visible to us). This idea was a result of a couple of hour of chat with Bruce where I explained that I didn't want to enlarge the HeapTupleHeader, and he came up with the bit idea. -- Alvaro Herrera (<alvherre[a]dcc.uchile.cl>) "En las profundidades de nuestro inconsciente hay una obsesiva necesidad de un universo lógico y coherente. Pero el universo real se halla siempre un paso más allá de la lógica" (Irulan) ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings
