Boston Linux & Unix (BLU) Home | Calendar | Mail Lists | List Archives | Desktop SIG | Hardware Hacking SIG
Wiki | Flickr | PicasaWeb | Video | Maps & Directions | Installfests | Keysignings
Linux Cafe | Meeting Notes | Blog | Linux Links | Bling | About BLU

BLU Discuss list archive

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

shells and bells

On Wed, 3 May 2000, Derek Martin wrote:

> While I can't speak to Mike's assertions about ODBC or locking, the only
> alternative I know of to DBMS-supported on-line back up is to shut down
> the database and dump it to text files, which can then be backed up.  
> Otherwise, as Mike said, you have no guarantee that the data on the disk
> is in a form which is useful to back up, and it's rather likely that it
> won't be.
> As I understand the problem (and I'll admit up front that my understanding
> may be flawed), this is due to the fact that a database write, while
> "atomic" from the database's perspective, is not an atomic operation from
> the kernel's perspective, unless the whole operation can be done with
> exactly one system call (system calls are guaranteed to be atomic, IIRC).
> Otherwise, the dbms may finish its time slice while a record update is in
> progress, at which time the back-up program may read the database's files,
> yeilding spaghetti data on your backup tape.

This is why during a backup procedure you READ LOCK the mysql database.
Clients will still be able to query the database,. The better way would be
to do a local lock, which would also allow INSERTS during the process, and
then dump the SQL data from the database (which is not what you folks are
talking about).
> > 
> > Mysql uses a locking method they call "atomic operations" (I'm not
> The term "atomic operation" is certainly not a MySQL-ism... it refers to
> an operation that must complete before any other operation can begin.  It
> is certainly possible for MySQL to consider its record updates atomic,
> while in the framework of the OS they are not.  Wether or not that is
> actually the case, I can't say...

I knew I should have double-double quoted it. ;)

I know what an atomic operation is, I just didn't know if it was only
mysql applying the description to the way their DBMS works or if other
DBMS vendors use the term.

Niall Kavanagh, niall at
News, articles, and resources for web professionals and developers:

Subcription/unsubscription/info requests: send e-mail with
"subscribe", "unsubscribe", or "info" on the first line of the
message body to discuss-request at (Subject line is ignored).

BLU is a member of BostonUserGroups
BLU is a member of BostonUserGroups
We also thank MIT for the use of their facilities.

Valid HTML 4.01! Valid CSS!

Boston Linux & Unix /