Re: V4 of PITR performance improvement for 8.4

Fujii Masao wrote:
> Hi,
> 
> On Mon, Mar 9, 2009 at 10:20 PM, Heikki Linnakangas
> <heikki.linnakangas@enterprisedb.com> wrote:
>> Thanks. This patch seems to be missing the new readahead.c file. I grabbed
>> that from the previous patch version.
> 
> Oh, sorry for the mistake. I changed one of Suzuki-san's patches
> to be rebased to HEAD again (readahead-20090310.patch).
> The other (addShBufCheck-20090120.patch) is not changed.
> 
> Comment:
> we might reach consistent recovery state *before* redoing the safe
> starting point, because readahead slightly delays the actual redo.
> Is this safe? 

No. If you haven't replayed all the WAL records up to the safe starting 
point, the database isn't consistent yet. The distinction doesn't matter 
in practice without Hot Standby, though.

> If not, the readahead queue should be flushed before
> reaching that state?

Yes. Or you could move the reporting that you've reached the consistent 
recovery state into RedoRecords, when you reach the min safe starting point.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com