Re: Making metadata storage SQL-driven

[Jamie McCracken <jamiemcc blueyonder co uk>]

Alexander Larsson wrote:
> On Thu, 2005-09-01 at 12:21 +0100, Jamie McCracken wrote:
>
>
> > For instance the embedded mysql needs no set up and it will work out of 
> > the box (its just a shared library) so installation and setup is a 
> > non-issue. It has no locking issues as the INNODB stuff in mysql is 
> > multi generational so readers and writers dont block each other and its 
> > totally safe as a write generates a new copy of a record and the commit 
> > on it is atomic so even of there's a power failure during a write 
> > corruption will not occur to anything committed.
>
>
> How does this work with shared NFS homedirs? Writes are not atomic there
> the same way they are for local filesystems, so how could you make the
> commit atomic.

I dont know the internal details of mysql but generally casue the 
generation architecture is journalised a new write creates a copy of the 
exisiting record which once completed will have a flag on the record to 
indicate whether its committed or not. So once the user has written the 
changes, the user will call commit to set that flag. If power failure 
occurs the record will either be committed (the flag set) or not (in 
which case that copy is discarded and lost forever). To benefit from 
this forced writes need to be used.



> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>  Alexander Larsson                                            Red Hat, Inc 
>                    alexl redhat com    alla lysator liu se 
> He's an otherworldly soccer-playing photographer from a doomed world. She's a 
> hard-bitten gypsy soap star who dreams of becoming Elvis. They fight crime! 


--
Mr Jamie McCracken
http://www.advogato.org/person/jamiemcc/