Hi Jan,
The only place fsync is called after AIO that I could find is in
function buf_LRU_remove_pages
(buf0lru.cc)
But after other AIO operations, I didn't see fsync is called.
Do you know how this difference will affect the recovery process? Thanks.
Xiaofei
On Wed, May 6, 2015 at 8:24 PM, Jan Lindström <jan.lindst...@mariadb.com>
wrote:
> Hi,
>
> There is sync for AIO pages also. There is no dirty page table but
> naturally dirty pages are marked and they are on LRU list see
> buf/buf0lru.cc.
>
> R: Jan
>
> On Thu, May 7, 2015 at 12:23 AM, Xiaofei Du <xiaofei.du...@gmail.com>
> wrote:
>
>> Hi Jan,
>>
>> Thanks for clarification. I should have used synchronous write, instead
>> of synchronous flush. My point is that I noticed for sync writes, fsync is
>> called to force pages to be on persistent storage. while for AIO pages,
>> fsync is not called to force pages to be on persistent storage. My question
>> here is why fsync is required for sync IOs. Does InnoDB maintain a dirty
>> page table? Is fsync called to guarantee the page to be on persistent
>> storage so that the dirty page table can be updated? If this is the case,
>> when is the dirty page table updated for asynchronous IOs?
>>
>> P.S. I couldn't find code for dirty page table. So I am not sure if
>> InnoDB maintains a dirty page table for recovery. Could you please give me
>> a pointer to related code and related resources? Thanks.
>>
>> Xiaofei
>>
>> On Wed, May 6, 2015 at 10:12 AM, Jan Lindström <jan.lindst...@mariadb.com
>> > wrote:
>>
>>> Hi,
>>>
>>> Terminology is little bit confusing here. Page flushing means that we
>>> have done synchronous write to disk but that does not mean that write is
>>> physically on device yet, therefore there is flush to force it to
>>> persistent storage.
>>>
>>> R: Jan
>>>
>>> On Wed, May 6, 2015 at 12:57 AM, Xiaofei Du <xiaofei.du...@gmail.com>
>>> wrote:
>>>
>>>> Hello,
>>>>
>>>> When a dirty page is flushed synchronously in buf_flush_write_block_low
>>>> ,
>>>> fsync is called in the following snippet. I am wondering why
>>>> we need this fsync for synchronous flush? The record should be in
>>>> the log already, so recovery should be able to successfully redo it
>>>> and apply to the disk during recovery. Maybe I am missing something
>>>> here,
>>>> please let me know if I am wrong. Thanks much!
>>>>
>>>> Xiaofei
>>>>
>>>>
>>>> /* When doing single page flushing the IO is done synchronously and we
>>>> flush the changes to disk only for the tablespace we are working on. */ if
>>>> (sync) { ut_ad(flush_type == BUF_FLUSH_SINGLE_PAGE);
>>>> fil_flush(buf_page_get_space(bpage));
>>>> /* true means we want to evict this page from the LRU list as well. */
>>>> buf_page_io_complete(bpage, true); }
>>>>
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>>>
>>
>
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