Re: MySQL Reengineering Project

[Sergei Golubchik]

Hi, Brian!

On May 12, Brian Aker wrote:
> 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;
> }

Yes, I've seen that :)

> 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).

Right, I remember. It was inconvenient, indeed.

The main reason, of course, was that we don't have a clean external
storage engine API (compare with fulltext parser plugins - no API
changes in three years).

Still, this could've been fixed differently, without a void* pointer.

>>  - 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++).

write_row() as you know, and as was mentioned in this thread, doesn't
use its argument at all. We could just as well declare it as a method
without arguments. At least it would've been less misleading.

>>> 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.

Ah, okay. I see.

I thought that "parallelization", that Jay mentioned, means executing
parts of a single statement in different threads - which, indeed, may
need two THDs sharing the same Statement.

Regards / Mit vielen Grüßen,
Sergei

-- 
   __  ___     ___ ____  __
  /  |/  /_ __/ __/ __ \/ /   Sergei Golubchik <serg@stripped>
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