Re: questions on undo log

Hi, sunny

On Wed, Feb 8, 2012 at 9:50 AM, Sunny Bains <[email protected]> wrote:
> Xuekun,
>
> On 08/02/2012, at 12:02 PM, Xuekun Hu wrote:
>
>> Hi, Libing
>>
>> Many thanks. From the file page types definition, I found
>> FIL_PAGE_UNDO_LOG which should represent the undo log page in buffer
>> pool. So it also means every change to undo log page in buffer pool
>> also follows the page flushing mechanism of buffer pool (writing to
>> disk in background, writing to doublewrite buffer, writing the changes
>> to transaction log etc). My understanding is right?
>>
>> However I also think it is not very accurate about "Innodb buffer pool
>> is for all things in table spaces" like you said. :-) I think it
>> should exclude the data dictionary which has own memory cache and
>> doublewrite buffer. :-)
>
> Song Libing is correct.  The data dictionary cache is simply another view
> of the data dictionary that is on disk. There is no separate buffer pool
> for the dictionary cache and it doesn't have a separate double write buffer.
>

Sorry, I don't quite understand the meanings of "separate". You mean
the dictionary cache is a part of buffer pool? Also the 2MB of
doublewrite buffer in memory  is also a part of buffer pool?

> Hope that helps.
>
> Regards,
> -sunny

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