Re: fsync, ext2 on Linux

On Mon, 1 Nov 2004, Oliver Jowett wrote:

> Heikki Linnakangas wrote:
>> The Linux fsync man page says:
>> 
>> "It does not necessarily ensure that the entry in the directory containing 
>> the file has also reached disk. For that an explicit fsync on the file 
>> descriptor of the directory is also needed."
>> 
>> AFAIK, we don't care about it at the moment. The actual behaviour depends 
>> on the filesystem, reiserfs and other journaling filesystems probably don't 
>> need the explicit fsync on the parent directory, but at least ext2 does.
>> 
>> I've experimented with a user-mode-linux installation, crashing it at 
>> specific points. It seems that on ext2, it's possible to get the database 
>> in non-consistent state.
>
> Have you experimented with mounting the filesystem with the dirsync option 
> ('-o dirsync') or marking the log directory as synchronous with 'chattr +D'? 
> (no, it's not a real fix, just another data point..)

Quick experiment shows that they seem to fix it as expected.

"chattr +D" might not be such a bad idea. A warning would be nice if you 
start the postmaster on a filesystem that requires it. Few admins would 
remember/know about it otherwise.

- Heikki