Re: WAL

Torsten Förtsch wrote:
> if I do something like this:
>
> BEGIN;
> UPDATE tbl SET data='something' WHERE pkey='selector';
> UPDATE tbl SET data=NULL WHERE pkey='selector';
> COMMIT;
>
> Given 'selector' actually exists, I get a separate WAL entry for each of the updates. My question is,
> does the first update actually hit the data file?

It should, yes.

> If I am only interested in the first update hitting the WAL, does it make sense to do something like
> the above in a transaction? Would that help to keep the table small in a high concurrency situation?
> The table itself has a small fillfactor. So, in most cases there should be enough space to do a HOT
> update. For that HOT update, is that second update setting data to NULL beneficial or rather adverse?

How could the second update *not* be WAL logged?

Maybe you could explain what you are trying to achieve.

Yours,
Laurenz Albe