highlight experimental nature of lidar
#### <sub><sup><a name="v560-note-4202" href="#v560-note-4202">:link:</a></sup></sub> feature
-* Resource checking has changed, but (hopefully) you won't notice!
+* There is a a new experimental method of resource checking, which is off by default but can be turned on via `CONCOURSE_ENABLE_LIDAR`.
The entire system has been redesigned to be asynchronous, but that shouldn't have any affect on your existing workflows. `fly check-resource` and `fly check-resource-type` will continue to work the way you expect them to (except for a small change to the command output). In addition you can now specify an `--async` flag if you don't want to wait for the check to finish.
It's worth noting that concourse performs a lot of checks (like A LOT). Since we're now storing checks in the database, this table will tend to grow very quickly. By default checks get gc'ed every 6 hrs, but this interval can be configured by specifying a `CONCOURSE_GC_CHECK_RECYCLE_PERIOD`. If you want to reduce the number of checks that happen, you can start making heavier use of the `webhook` endpoint to trigger checks from external sources. This allows you to significantly reduce the `check_every` interval (default 1m) for your resource without impacting the time it takes to schedule a build.
- If you're interested in more detail about what changed you can have a look at the corresponding PR #4202 or the initial issue #3788
+ If you're interested in more detail about what changed you can have a look at the corresponding PR #4202 or the initial issue #3788.
- This feature is off by default but can be turned on via `CONCOURSE_ENABLE_LIDAR`.
#### <sub><sup><a name="v560-note-4417" href="#v560-note-4417">:link:</a></sup></sub> feature
