maria-discuss team mailing list archive

[Xiaofei Du <xiaofei.du008@xxxxxxxxx>]

Laurynas,

This is exactly what I was looking for. I went through these functions
before. I disabled double write buffer, so I didn't pay attention to code
under buf_dblwr... The reason I asked this question is because I didn't
know how the recovery process works, so I was wondering if it's necessary
to fsync after each write. It's a performance concern. Anyway, thank you
very much!

Jan -- Thank you for your answer too!

Xiaofei

On Thu, May 7, 2015 at 9:59 PM, Laurynas Biveinis <
laurynas.biveinis@xxxxxxxxx> wrote:

> Xiaofei -
>
> fsync is performed for all the flush types (LRU, flush, single page)
> if it is asked for (innodb_flush_method != O_DIRECT_NO_FSYNC). The
> apparent difference in sync and async is not because of the sync
> difference itself, but because of the flush type difference. The
> single page flush flushes one page, and requests a fsync for its file.
> Other flushes flush in batches, don't have to fsync for each written
> page individually but rather sync once at the end. Then doublewrite
> complicates this further. If it is disabled, fsync will happen in
> buf_dblwr_sync_datafiles called from buf_dblwr_flush_buffered_writes
> called from buf_flush_common called at the end of either LRU or flush
> list flush. If doublewrite is enabled, fsync will happen in
> buf_dblwr_update called from buf_flush_write_complete.
>
>
>
>
> 2015-05-07 9:01 GMT+03:00 Xiaofei Du <xiaofei.du008@xxxxxxxxx>:
> > Hi Laurynas,
> >
> > On Wed, May 6, 2015 at 9:14 PM, Laurynas Biveinis
> > <laurynas.biveinis@xxxxxxxxx> wrote:
> >>
> >> Xiaofei -
> >>
> >> > Does InnoDB maintain a dirty
> >> > page table?
> >>
> >> You must be referring to the buffer pool flush_list.
> >
> >
> > You are right. The flush_list is can be used for recovery and checkpoint.
> >
> >>
> >>
> >> > 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?
> >>
> >> Check buf_flush_write_complete in buf0flu.cc. For async IO it is
> >> called from buf_page_io_complete in buf0buf.cc.
> >
> >
> > You are right that this is the place it updates the dirty page
> information.
> > But I still don't understand why the fsync is needed for synchronous IOs,
> > but not for the AIOs. Jan Lindstrom said fsync is also called for other
> AIO
> > operations. But I could only it true in one of many AIO operations. Or
> maybe
> > I am missing something still?
> >
> >>
> >>
> >> --
> >> Laurynas
> >
> >
>
>
>
> --
> Laurynas
>