Horton

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

John Naylor <john.naylor@2ndquadrant.com>

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From: John Naylor <john.naylor@2ndquadrant.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Mithun Cy <mithun.cy@enterprisedb.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2019-01-24T19:33:03Z
Lists: pgsql-hackers 
On Wed, Jan 23, 2019 at 11:17 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Thu, Jan 24, 2019 at 3:39 AM John Naylor <john.naylor@2ndquadrant.com> wrote:
> > mkdir -p data1 data2 standby
> >
> > echo 'heap' > data1/foo
> > echo 'fsm' > data1/foo_fsm
> >
> > # simulate streaming replication
> > rsync --archive data1 standby
> >
> > # simulate pg_upgrade, skipping FSM
> > ln data1/foo -t data2/
> >
> > rsync --archive --delete --hard-links --size-only --no-inc-recursive
> > data1 data2 standby
> >
> > # result
> > ls standby/data1
> > ls standby/data2
> >
> >
> > The result is that foo_fsm is not copied to standby/data2, contrary to
> > what the docs above imply for other unlinked files. Can anyone shed
> > light on this?
> >
>
> Is foo_fsm present in standby/data1?

Yes it is.

> I think what doc means to say is
> that it copies any unlinked files present in primary's new cluster
> (which in your case will be data2).

In that case, I'm still confused why that doc says, "Unfortunately,
rsync needlessly copies files associated with temporary and unlogged
tables because these files don't normally exist on standby servers."
I fail to see why the primary's new cluster would have these if they
weren't linked. And in the case we're discussing here, the skipped
FSMs won't be on data2, so won't end up in standby/data2.

-- 
John Naylor                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. Improve code comments in b0eaa4c51b.

  2. During pg_upgrade, conditionally skip transfer of FSMs.

  3. Add more tests for FSM.

  4. Doc: Update the documentation for FSM behavior for small tables.

  5. Make FSM test portable.

  6. Avoid creation of the free space map for small heap relations, take 2.

  7. Move page initialization from RelationAddExtraBlocks() to use, take 2.

  8. Avoid creation of the free space map for small heap relations.

  9. In bootstrap mode, don't allow the creation of files if they don't already