Re: WIP: Avoid creation of the free space map for small tables

On Mon, Jan 21, 2019 at 6:32 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> So we won't allow transfer of FSM files if their size is below
> HEAP_FSM_CREATION_THRESHOLD. What will be its behavior in link mode?
> It seems that the old files will remain there. Will it create any
> problem when we try to create the files via the new server, can you
> once test this case?

I tried upgrading in --link mode, and on the new cluster, enlarging
the table past the threshold causes a new FSM to be created as
expected.

> Also, another case to think in this regard is the upgrade for standby
> servers, if you read below paragraph from the user manual [1], you
> will see what I am worried about?
>
> "What this does is to record the links created by pg_upgrade's link
> mode that connect files in the old and new clusters on the primary
> server. It then finds matching files in the standby's old cluster and
> creates links for them in the standby's new cluster. Files that were
> not linked on the primary are copied from the primary to the standby.
> (They are usually small.)"
>
> [1] - https://www.postgresql.org/docs/devel/pgupgrade.html

Trying this, I ran into a couple problems. I'm probably doing
something wrong, but I can't help but think there's a pg_upgrade
bug/feature I'm unaware of:

I set up my test to have primary directory data1 and for the secondary
standby/data1. I instructed pg_upgrade to upgrade data1 into data1u,
and I tried the rsync recipe in the docs quoted above, and the
upgraded standby wouldn't go into recovery. While debugging that, I
found surprisingly that pg_upgrade also went further and upgraded
standby/data1 into standby/data1u. I tried deleting standby/data1u
before running the rsync command and still nothing. Because the
upgraded secondary is non-functional, I can't really answer your
question.

Not sure if this is normal, but the pg_upgraded new cluster no longer
had the replication slot. Re-adding it didn't allow my upgraded
secondary to go into recovery, either. (I made sure to copy the
recovery settings, so that can't be the problem)

--
John Naylor https://www.2ndQuadrant.com/
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