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: 2019-01-27T21:03:22Z
Lists: pgsql-hackers

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On Sat, Jan 26, 2019 at 2:14 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Sat, Jan 26, 2019 at 5:05 AM John Naylor <john.naylor@2ndquadrant.com> wrote:
> >
> > So, in v19 we check pg_class.relpages and if it's
> > a heap and less than or equal the threshold we call stat on the 0th
> > segment to verify.
> >
>
> Okay, but the way logic is implemented appears clumsy to me.

> The function transfer_relfile has no clue about skipping of FSM stuff,
> but it contains comments about it.

Yeah, I wasn't entirely happy with how that turned out.

> I think there is some value in using the information from
> this function to skip fsm files, but the code doesn't appear to fit
> well, how about moving this check to new function
> new_cluster_needs_fsm()?

For v21, new_cluster_needs_fsm() has all responsibility for obtaining
the info it needs. I think this is much cleaner, but there is a small
bit of code duplication since it now has to form the file name. One
thing we could do is form the the base old/new file names in
transfer_single_new_db() and pass those to transfer_relfile(), which
will only add suffixes and segment numbers. We could then pass the
base old file name to new_cluster_needs_fsm() and use it as is. Not
sure if that's worthwhile, though.

> The order in which relkind and relpages is used in the above code is
> different from the order in which it is mentioned in the query, it
> won't matter, but keeping in order will make look code consistent.  I
> have made this and some more minor code adjustments in the attached
> patch.  If you like those, you can include them in the next version of
> your patch.

Okay, done.

-- 
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