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: Pavan Deolasee <pavan.deolasee@gmail.com>
Cc: Peter Geoghegan <pg@bowt.ie>, Alvaro Herrera <alvherre@2ndquadrant.com>, Bruce Momjian <bruce@momjian.us>, Haribabu Kommi <kommi.haribabu@gmail.com>, Jaime Casanova <jaime.casanova@2ndquadrant.com>, Robert Haas <robertmhaas@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-03-26T03:29:00Z
Lists: pgsql-hackers 
On Sat, Mar 25, 2017 at 11:24 PM, Pavan Deolasee
<pavan.deolasee@gmail.com> wrote:
>
> On Sat, 25 Mar 2017 at 11:03 PM, Peter Geoghegan <pg@bowt.ie> wrote:
>>
>> On Sat, Mar 25, 2017 at 12:54 AM, Amit Kapila <amit.kapila16@gmail.com>
>> wrote:
>> > I am not sure how do you want to binary compare two datums, if you are
>> > thinking datumIsEqual(), that won't work.  I think you need to use
>> > datatype specific compare function something like what we do in
>> > _bt_compare().
>>
>> How will that interact with types like numeric, that have display
>> scale or similar?
>>
>  I wonder why Amit thinks that datumIsEqual won't work once we convert the
> heap values to index tuple and then fetch using index_get_attr. After all
> that's how the current index tuple was constructed when it was inserted.

I think for toasted values you need to detoast before comparison and
it seems datamIsEqual won't do that job.  Am I missing something which
makes you think that datumIsEqual will work in this context.

> In
> fact, we must not rely on _bt_compare because that might return "false
> positive" even for two different heap binary values  (I think).

I am not telling to rely on _bt_compare, what I was trying to hint at
it was that I think we might need to use some column type specific
information for comparison.  I am not sure at this stage what is the
best way to deal with this problem without incurring non trivial cost.

-- 
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