Based on this, I think we should just implement the TRUNCATE/DROP option for the table, and avoid the idea of allowing non-logged operations on a table that has any data we want recovered after a crash.
--------------------------------------------------------------------------- Simon Riggs wrote: > On Thu, 2006-01-05 at 12:27 -0500, Bruce Momjian wrote: > > > Seems like a nice optimization. > > Negative thoughts: Toast tables have a toast index on them, yes? We have > agreed that we cannot use the optimization if we have indexes on the > main table. It follows that we cannot use the optimization if we have > *any* toasted data, since that would require a pointer between two > blocks, which would not be correctly recovered following a crash. If we > log the toast table then there could be a mismatch between heap and > toast table; if we don't log the toast table there could be a mismatch > between toast table and toast index. > > We can test to see if the toast table is empty when we do ALTER TABLE, > but loading operations may try to create toasted data rows. > > Presumably that means we must either: > i) abort a COPY if we get a toastable value > ii) if we get a toastable value, insert the row into a new block, which > we do logging of, then also log the toast insert and the toast index > insert - i.e. some blocks we log, others not > > This is still useful for many applications, IMHO, but the list of > restrictions seems to be growing. Worse, we wouldn't know that the toast > tables were empty until after we did the COPY TO for a pg_dump, so we > wouldn't be able to retrospectively add an ALTER TABLE command ahead of > the COPY. > > Thoughts? Hopefully there are some flaws in my thinking here, > > Best Regards, Simon Riggs > > > -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
