On Wed, May 4, 2016 at 4:02 PM, Alex Ignatov <a.igna...@postgrespro.ru> wrote:
> > > On 03.05.2016 2:17, Tom Lane wrote: > >> Alex Ignatov <a.igna...@postgrespro.ru> writes: >> >>> I think that rename can help a little bit. At least on some FS it is >>> atomic operation. >>> >> >> Writing a single sector ought to be atomic too. I'm very skeptical that >> it'll be an improvement to just move the risk from one filesystem >> operation to another; especially not to one where there's not even a >> terribly portable way to request fsync. >> >> regards, tom lane >> >> >> pg_control is 8k long(i think it is legth of one page in default PG > compile settings). > I also think that 8k recording can be atomic. Even if recording of one > sector is atomic nobody can say about what sector from 8k record of > pg_control should be written first. It can be last sector or say sector > number 10 from 16. The actual data written is always sizeof(ControlFileData) which should be less than one sector. I think it is only possible that we get a torn write for pg_control, if while writing + fsyncing, the filesystem maps that data to different sectors. With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
