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.bivei...@gmail.com> 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.du...@gmail.com>: > > Hi Laurynas, > > > > On Wed, May 6, 2015 at 9:14 PM, Laurynas Biveinis > > <laurynas.bivei...@gmail.com> 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 >
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