Re: Trying to understand soft vs hard commit vs transaction log

[Shawn Heisey]

On 2/8/2013 3:12 AM, Isaac Hebsh wrote:
Shawn, what about 'flush to disk' behaviour on MMapDirectoryFactory?

MMapDirectoryFactory should flush everything to disk on a hard commit 
and not keep anything in RAM.  I *think* that soft commits still end up 
in RAM with this implementation, but you'll want to wait for someone who 
actually knows to confirm or deny that.

Just FYI, NRTCachingDirectoryFactory is a wrapper class - implementing 
caching functionality and using MMapDirectoryFactory to actually contact 
the disk.

If indexing and/or startup performance concerns have led you to turn off 
the updateLog, MMapDirectoryFactory is the correct implementation to 
use.  Using the NRT default without the updateLog will lead to data loss 
if anything crashes.

Thanks,
Shawn