Re: Making metadata storage SQL-driven

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

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