Re: Reduce WAL logging of INSERT SELECT

Jeff Davis wrote:
> On Thu, 2011-08-04 at 17:46 -0400, Bruce Momjian wrote:
> > Right.  I brought up SELECT INTO because you could make the argument
> > that INSERT ... SELECT is not a utility command like the other ones and
> > therefore can't be done easily, but CREATE TABLE AS is internal SELECT
> > INTO and implemented in execMain.c, which I think is where INSERT ...
> > SELECT would also be implemented.
> 
> The above statement is a little confusing, so let me start from the
> beginning:
> 
> How could we avoid WAL logging for INSERT ... SELECT?
> 
> The way we do it for CREATE TABLE AS is because nobody would even *see*
> the table if our transaction doesn't commit. Therefore we don't need to
> bother logging it. Same can be said for SELECT INTO.
> 
> INSERT ... SELECT is just an insert. It needs just as much logging as
> inserting tuples any other way. For instance, it will potentially share
> pages with other inserts, and better properly record all such page
> modifications so that they return to a consistent state.

It would act like COPY, meaning the table would have to be truncated or
created in the same transaction.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + It's impossible for everything to be true. +