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)
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