Temporarily turn off the background fetch until it gets re-worked

[vkuzniet]

Signed-off-by: Viktor Kuznietsov vkuzniet@amazon.com

Issue #, if available:

Description of changes:
Temporarily turning off the background fetch until it gets re-worked. For more details see the issue #106

Testing performed:

• make test && make check && make integration pass
• Deployed soci-snapshotter-grpc and soci to an EC2 instance, created an index for rethinkdb and ran the container workload in lazy loading mode. Observed no log record referring to background fetcher.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[hanyuel]

With this change, even when a user passes in NoBackgroundFetch=false in config parameter for running the snapshotter, the background fetch will not run. I don’t think we should silently not run the bg fetch w/o any message when user explicitly sets the background fetch on. Sure the background fetch will be re-designed, but today it still can run. I suggest changing the behavior to not running the background fetch if no bg fetch config pass in from the user, and using the config from the user if provided.

[vkuzniet]

With this change, even when a user passes in NoBackgroundFetch=false in config parameter for running the snapshotter, the background fetch will not run. I don’t think we should silently not run the bg fetch w/o any message when user explicitly sets the background fetch on. Sure the background fetch will be re-designed, but today it still can run. I suggest changing the behavior to not running the background fetch if no bg fetch config pass in from the user, and using the config from the user if provided.

It is usually on by default. There's a config option to turn it off. The problem with intelligent handling there is that the config.toml is being deserialized into config struct and there's no way to know if the user set this field or it was set by default.
If we agree that background fetcher as it is right now interferes with on-demand fetches, and it does seem so, then the easiest thing is to turn it off temporarily.

Another option would be to keep it disabled by default, e.g. name the option as toml:background_fetch_enabled, which will be set to false by default. In this case, the likelihood of someone enabling it would be much smaller.

[sbuckfelder]

I'm comfortable with this