2014-04-17 11:11 GMT+02:00 Ajay Garg <ajaygargn...@gmail.com>: > On Thu, Apr 17, 2014 at 2:28 PM, Reindl Harald <h.rei...@thelounge.net > >wrote: > > > > > > > Am 17.04.2014 10:55, schrieb Ajay Garg: > > > I do understand the meaning of Unix "sync" function. > > > > > > So, you mean to say that "flushing" and "syncing" are same, in the > > context of MySQL? > > > > please get rid of top-posting and reply-all > > > > a flush without a sync is "dear operating system, may i ask you to write > > that to disk if you find the time to do so" while a sync is "write that > > to disk" without a nice asking > > > > Thanks Reindl, that clears it up !!
Keep in mind that if you are using HW RAID controller (and a BBU) the concept of write-back and write-through are important to have in mind too whilst thinking about how and when your data is written to disk. If you enable sync_binlog and trx_commit to 1, it might not necessarily be committing on every transaction to disk, as it might depend on how you've configured your controller. If you have write-through configured, the data will be written to disk and cache at the same time (this has a performance drawback). If you have write-back configured, the data will be written to cache (and then to disk, but _not_ at the same time) so you might lose data if there's a power failure. When you have write-back, at an OS level your data has been sync'ed to disk even though this is not totally true. write-back is better for performance, but you have to keep in mind that you can lose data (which is not common, but you're not 100% safe). Hope this helps Manuel.
