[lug] mysqldump versus snapshot versus..

[Nate Duehr]

dio2002 at indra.com wrote:
>> Most real databases write updates to the transaction log, and once
>> they're written to the transaction log, they then write them to the
>> underlying tables.
>>
>> A backup process usually just suspends the writer process from doing
>> this until the backup completes.
>>
>> Of course, where this gets icky is when you have someone reading. The
>> engine has to check the transaction log to see if the rows it's
>> returning are affected by an update, and if so, return those.
> 
> that simple tidbit explains in layman's terms how "real" dbs get around
> the lock tables problem.  thanks for sharing it.  it clarifies the matter
> for me a whole lot.

There's some interesting trade-offs when designing the setup, since you 
want transaction logs not to be rotating constantly (too much I/O) but 
you also don't want full scans of full logs to take forever...

:-)

Nate