Re: New strategies for freezing, advancing relfrozenxid early

On Mon, Jan 9, 2023 at 7:16 AM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
>
> On Tue, Jan 3, 2023 at 12:30 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> > Attached is v14.
>
> This has stopped applying due to conflicts with nearby work on VACUUM
> from Tom. So I attached a new revision, v15, just to make CFTester
> green again.
>
> I didn't have time to incorporate any of the feedback from Matthias
> just yet. That will have to wait until v16.
>
I have looked into the patch set, I think 0001 looks good to me about
0002 I have a few questions, 0003 I haven't yet looked at

1.
+ /*
+ * Finally, set tableagefrac for VACUUM. This can come from either XID or
+ * XMID table age (whichever is greater currently).
+ */
+ XIDFrac = (double) (nextXID - cutoffs->relfrozenxid) /
+ ((double) freeze_table_age + 0.5);

I think '(nextXID - cutoffs->relfrozenxid) / freeze_table_age' should
be the actual fraction right? What is the point of adding 0.5 to the
divisor? If there is a logical reason, maybe we can explain in the
comments.

2.
While looking into the logic of 'lazy_scan_strategy', I think the idea
looks very good but the only thing is that
we have kept eager freeze and eager scan completely independent.
Don't you think that if a table is chosen for an eager scan
then we should force the eager freezing as well?

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com