From: Zardosht Kasheff
Date: March 2 2010 10:47pm
Subject: Re: unique_checks and InnoDB primary key
List-Archive: http://lists.mysql.com/internals/37764
Message-Id: <2f9663ba1003021447w2ec6f871gcf4e565c34b48fa1@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

Then what does one gain by setting unique_checks to 0 and using InnoDB?

On Tue, Mar 2, 2010 at 5:35 PM, Sunny Bains <Sunny.Bains@stripped> wrote:
> Zardosht,
>
> On 03/03/2010, at 1:54 AM, Zardosht Kasheff wrote:
>
>> Hello,
>>
>> I have a question about the variable unique_checks and InnoDB. I see
>> that if unique_checks is 0, the storage engine is allowed to ignore
>> duplicates of secondary unique keys. InnoDB uses this setting to allow
>> the insert buffer to increase insertion speed.
>>
>> My question is this: if unique_checks is 0, is InnoDB allowed to
>> ignore duplicates of the primary key? Looking at code, the answer
>> seems to be no. And as a result, the insert buffer is not used for the
>> primary key, correct?
>>
>> Assuming my understanding above is correct, here is a follow up
>> question. Suppose I have a table schema:
>> create table foo (a int, b int, primary key (a,b))engine=3DInnoDB;
>> Because the insert buffer cannot be used for the primary key, can I
>> get better performance by changing the schema to the following?
>> create table foo (a int, b int, unique key (a,b))engine=3DInnoDB;
>>
>> Or will this not work because InnoDB selects the unique key as the
>> clustered key?
>>
>> Thanks
>> -Zardosht
>
> Unique secondary keys cannot use the insert buffer. =A0Also, he insert bu=
ffer
> is not used for primary keys at all. =A0The insert buffer is only used fo=
r
> non-unique secondary indexes.
>
> Regards,
> -sunny
>