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: Alvaro Herrera <alvherre@2ndquadrant.com>, Robert Haas <robertmhaas@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: 2017-03-29T06:39:28Z
Lists: pgsql-hackers 
On Tue, Mar 28, 2017 at 10:31 PM, Pavan Deolasee
<pavan.deolasee@gmail.com> wrote:
>
> On Tue, Mar 28, 2017 at 4:05 PM, Amit Kapila <amit.kapila16@gmail.com>
> wrote:
>>
>> As asked previously, can you explain me on what basis are you
>> considering it robust?  The comments on top of datumIsEqual() clearly
>> indicates the danger of using it for toasted values (Also, it will
>> probably not give the answer you want if either datum has been
>> "toasted".).
>
>
> Hmm. I don' see why the new code in recheck is unsafe. The index values
> themselves can't be toasted (IIUC), but they can be compressed.
> index_form_tuple() already untoasts any toasted heap attributes and
> compresses them if needed. So once we pass heap values via
> index_form_tuple() we should have exactly the same index values as they were
> inserted. Or am I missing something obvious here?
>

I don't think relying on datum comparison for compressed values from
heap and index is safe (even after you try to form index tuple from
heap value again during recheck) and I have mentioned one of the
hazards of doing so upthread.  Do you see any place else where we rely
on comparison of compressed values?

-- 
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