Re: BTRFS for OLTP Databases

[linux-btrfs@adrb.pl]

W dniu 2017-02-13 o 13:44 PM, Austin S. Hemmelgarn pisze:
> On 2017-02-09 22:58, Andrei Borzenkov wrote:
>> 07.02.2017 23:47, Austin S. Hemmelgarn пишет:
>> ...
>>> Sadly, freezefs (the generic interface based off of xfs_freeze) only
>>> works for block device snapshots.  Filesystem level snapshots need the
>>> application software to sync all it's data and then stop writing until
>>> the snapshot is complete.
>>>
>>
>> I expect databases to be using directio, otherwise we have problems even
>> without using snapshots. Is it still an issue with directio?
> It is less of an issue, but it's still an issue because you can still
> call for snapshot creation in the middle of an application I/O
> request. In other words, the application wouldn't need to worry about
> syncing data, but it would need to worry about making sure it's not
> actually writing anything when the snapshot happens.
>
I think this should work the other way around. Snapshot should wait
until all directio writes are done,

and new requests sent when creating snapshot, should wait until snapshot
is done.


-- 

Adrian Brzeziński