| From: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
|---|---|
| To: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> |
| Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Jaime Casanova <jaime(dot)casanova(at)2ndquadrant(dot)com>, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Patch: Write Amplification Reduction Method (WARM) |
| Date: | 2017-03-27 11:15:40 |
| Message-ID: | CAA4eK1J7ThxvVc0DN9KgX04scFjzHoZSNhD4PSwmF7bfTzfQsA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sat, Mar 25, 2017 at 1:24 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Fri, Mar 24, 2017 at 11:49 PM, Pavan Deolasee
> <pavan(dot)deolasee(at)gmail(dot)com> wrote:
>>
>> On Fri, Mar 24, 2017 at 6:46 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
>> wrote:
>>>
>
>> While looking at this problem, it occurred to me that the assumptions made
>> for hash indexes are also wrong :-( Hash index has the same problem as
>> expression indexes have. A change in heap value may not necessarily cause a
>> change in the hash key. If we don't detect that, we will end up having two
>> hash identical hash keys with the same TID pointer. This will cause the
>> duplicate key scans problem since hashrecheck will return true for both the
>> hash entries.
Isn't it possible to detect duplicate keys in hashrecheck if we
compare both hashkey and tid stored in index tuple with the
corresponding values from heap tuple?
--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com
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