Re: Unlogged tables cleanup

On Wed, Dec 7, 2016 at 11:20 PM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> OK, I rewrote a bit the patch as attached. What do you think?

Committed and back-patched all the way back to 9.2.

>> Right (I think). If we set and clear delayChkpt around this work, we
>> don't need the immediate sync.
>
> My point is a bit different than what you mean I think: the
> transaction creating an unlogged relfilenode would not need to even
> set delayChkpt in the empty() routines because other transactions
> would not refer to it until this transaction has committed. So I am
> arguing about just removing the sync phase.

That doesn't sound right; see the comment for heap_create_init_fork.
Suppose the transaction creating the unlogged table commits, a
checkpoint happens, and then the operating system crashes. Without
the immediate sync, the operating system crash can cause the un-sync'd
file to crash, and because of the checkpoint the WAL record that
creates it isn't replayed either. So the file's just gone.

--
Robert Haas
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