| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com> |
| Cc: | Ryan Murphy <ryanfmurphy(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Does having a NULL column automatically exclude the table from the tupleDesc cache? |
| Date: | 2017-02-19 10:15:51 |
| Message-ID: | CA+Tgmobr7OVgeB=CZvrnk=o+5SpxN2EXTkWOh5ZwBTyrEF7vmA@mail.gmail.com |
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On Sat, Feb 18, 2017 at 12:33 AM, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com> wrote:
> On 2/15/17 1:37 PM, Ryan Murphy wrote:
>> attcacheoff can only be set positive for fields preceding any varlena
>> (typlen<0, but including the first such) or nullable values. I don't
>> know how much faster it is with the cache; you can measure it if your
>> curiosity is strong enough -- just set the first column to nullable.
>>
>> Thanks! Maybe I'll do some benchmarks.
>
> You'll probably want to do those at a C level, bypassing the executor. I
> would guess that executor overhead will completely swamp the effect of the
> cache in most cases.
That seems like it's kind of missing the point. If the tupleDesc
cache saves so little that it's irrelevant when tested through the
executor, it's not a very useful cache. I bet that's not the case,
though.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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