Re: questions on undo log

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.

Hope that helps.

Regards,
-sunny

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