[PLUG] FS to handle large files?

[Ian Burrell]

Kyle Hayes wrote:
> 
> From the manual, you cannot take a snapshot of the files used by the DB while 
> it is live.  MySQL can do this.  Because the manuals say this, I would assume 
> that something is in memory that isn't on disk.  Clearly this something can 
> be recreated (or rolled back) because Postgres can recover from crashes.  If 
> my snapshot isn't a completely safe and coherent set of data, it isn't a 
> snapshot.
> 

The manual doesn't really cover LVM snapshots.  It has been talked about 
on the mailing lists.  Normal copies of the database files won't work if 
the server is running; only an instantaneous snapshot will be 
consistent.  Now, the database and logs are consistent but they aren't 
in a known state.  That requires stopping the server.

> Can pg_dump be run safely and without performance degredation on a live 
> Postgres DB?
> 

The pg_dump can be slow for really large data sets.  I don't think it 
slows down serving queries.  It returns a consistent view of the 
database because it runs in a transaction.  It is possible to get 
individual databases in a known state but disabling client access before 
the dump.

  - Ian

-- 
ian at znark.com
http://www.znark.com/