From: Brian Aker
Date: May 12 2009 6:38pm
Subject: Re: MySQL Reengineering Project
List-Archive: http://lists.mysql.com/internals/36646
Message-Id: <A59F88AA-8305-45ED-92D5-F93A232621D4@tangent.org>
MIME-Version: 1.0 (Apple Message framework v930.3)
Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
Content-Transfer-Encoding: 7bit

Hi!

On May 12, 2009, at 11:14 AM, Sergei Golubchik wrote:

>  - init() function. Brian added that to pass handlerton down.
>    it is ignored by any clean plugin API and should've been done
>    differently for storage engines and I_S tables.

You should take a look at what Drizzle does as an example:

static int compressionudf_plugin_init(PluginRegistry &registry)
{
   registry.add(&compressudf);
   registry.add(&uncompressudf);
   registry.add(&uncompressed_lengthudf);
   return 0;
}

If I remember correctly the void * was used because before the  
solution you had devised required that every time we updated a  
structure we had to update every single plugin (and the original  
pointer change was done by Tomas Ulin, not myself).


>  - MYSQL_THD is defined as void*, which is fine as it's an opaque
>    pointer, plugins are never expected to look inside to cast it to
>    anything.

write_row() in the handler is another example of exposing vs  
encapsulation (which is fine... if you want to go with C over C++).

>> Without doing this, and using encapsulation so that a THD can have  
>> multiple
>> Statements, it will be very difficult to work on any future  
>> parallelization
>> efforts.
>
> You mean, a Statement can have multiple THDs, I suppose :)


No he means what he is saying. I don't know why you would want a  
statement shared across multiple THD, but having a THD be able to  
handle multiple statements means that you can do asynchronous queries  
within a single connection.

Cheers,
	-Brian