Greg Stark wrote: > > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > > I should be clearer. Suppose you have a table with a single index on > > the primary key. You are updating the row over and over again (a > > typical case). You create the first row, commit, then it is updated > > (two copies), commit, then you update it again. That first created row > > might not be visible to anyone, but has the same index value as the new > > row you are about to add. Why not reused that heap tuple? > > If you commit each update then your tuple might well be visible to other > transactions, how would you check that?
You check the xmin/xmax using standard visibility rules. > I originally thought you meant if you are repeatedly updating the same record > within the same transaction. In that case sure you could reuse the space but > a) only if it's big enough for the new record and b) how often do you really > do that? Right, that is a rare case. -- Bruce Momjian http://candle.pha.pa.us SRA OSS, Inc. http://www.sraoss.com + If your life is a hard drive, Christ can be your backup. + ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
