Horton

Re: Patch: Write Amplification Reduction Method (WARM)

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Pavan Deolasee <pavan.deolasee@gmail.com>, Bruce Momjian <bruce@momjian.us>, Jaime Casanova <jaime.casanova@2ndquadrant.com>, Haribabu Kommi <kommi.haribabu@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-03-21T10:51:24Z
Lists: pgsql-hackers 
On Fri, Mar 10, 2017 at 11:37 PM, Alvaro Herrera
<alvherre@2ndquadrant.com> wrote:
> Robert Haas wrote:
>> On Wed, Mar 8, 2017 at 2:30 PM, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
>> > Not really -- it's a bit slower actually in a synthetic case measuring
>> > exactly the slowed-down case.  See
>> > https://www.postgresql.org/message-id/CAD__OugK12ZqMWWjZiM-YyuD1y8JmMy6x9YEctNiF3rPp6hy0g@mail.gmail.com
>> > I bet in normal cases it's unnoticeable.  If WARM flies, then it's going
>> > to provide a larger improvement than is lost to this.
>>
>> Hmm, that test case isn't all that synthetic.  It's just a single
>> column bulk update, which isn't anything all that crazy,
>
> The problem is that the update touches the second indexed column.  With
> the original code we would have stopped checking at that point, but with
> the patched code we continue to verify all the other indexed columns for
> changes.
>
> Maybe we need more than one bitmapset to be given -- multiple ones for
> for "any of these" checks (such as HOT, KEY and Identity) which can be
> stopped as soon as one is found, and one for "all of these" (for WARM,
> indirect indexes) which needs to be checked to completion.
>

How will that help to mitigate the regression?  I think what might
help here is if we fetch the required columns for WARM only when we
know hot_update is false.

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com

Commits

  1. Implement SortSupport for macaddr data type

  2. Simplify check of modified attributes in heap_update

  3. Remove direct uses of ItemPointer.{ip_blkid,ip_posid}

  4. Fix CatalogTupleInsert/Update abstraction for case of shared indstate.

  5. Provide CatalogTupleDelete() as a wrapper around simple_heap_delete().

  6. Band-aid fix for incorrect use of view options as StdRdOptions.

  7. Update visibility map in the second phase of vacuum.

  8. Avoid having two copies of the HOT-chain search logic.

  9. Postgres95 1.01 Distribution - Virgin Sources