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: 2017-03-29T06:22:31Z
Lists: pgsql-hackers 
On Tue, Mar 28, 2017 at 10:35 PM, Pavan Deolasee
<pavan.deolasee@gmail.com> wrote:
>
> On Tue, Mar 28, 2017 at 7:04 PM, Amit Kapila <amit.kapila16@gmail.com>
> wrote:
>>
>>
>>
>>   For such an heap insert, we will pass
>> the actual value of column to index_form_tuple during index insert.
>> However during recheck when we fetch the value of c2 from heap tuple
>> and pass it index tuple, the value is already in compressed form and
>> index_form_tuple might again try to compress it because the size will
>> still be greater than TOAST_INDEX_TARGET and if it does so, it might
>> make recheck fail.
>>
>
> Would it? I thought  "if
> (!VARATT_IS_EXTENDED(DatumGetPointer(untoasted_values[i]))" check should
> prevent that. But I could be reading those macros wrong. They are probably
> heavily uncommented and it's not clear what each of those VARATT_* macro do.
>

That won't handle the case where it is simply compressed.  You need
check like VARATT_IS_COMPRESSED to take care of compressed heap
tuples, but then also it won't work because heap_tuple_fetch_attr()
doesn't handle compressed tuples.  You need to use
heap_tuple_untoast_attr() to handle the compressed case.  Also, we
probably need to handle other type of var attrs.  Now, If we want to
do all of that index_form_tuple()  might not be the right place, we
probably want to handle it in caller or provide an alternate API.


-- 
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