throttle-http docuemntation

Author: Shlomi Noach

doc/command-line-flags.md

@@ -131,6 +131,14 @@ See `approve-renamed-columns`
 
 Issue the migration on a replica; do not modify data on master. Useful for validating, testing and benchmarking. See [testing-on-replica](testing-on-replica.md)
 
+### throttle-control-replicas
+
+Provide a command delimited list of replicas; `gh-ost` will throttle when any of the given replicas lag beyond `--max-lag-millis`. The list can be queried and updated dynamically via [interactive commands](interactive-commands.md)
+
+### throttle-http
+
+Provide a HTTP endpoint; `gh-ost` will issue `HEAD` requests on given URL and throttle whenever response status code is not `200`. The URL can be queried and updated dynamically via [interactive commands](interactive-commands.md). Empty URL disables the HTTP check.
+
 ### timestamp-old-table
 
 Makes the _old_ table include a timestamp value. The _old_ table is what the original table is renamed to at the end of a successful migration. For example, if the table is `gh_ost_test`, then the _old_ table would normally be `_gh_ost_test_del`. With `--timestamp-old-table` it would be, for example, `_gh_ost_test_20170221103147_del`.

doc/interactive-commands.md

@@ -31,6 +31,7 @@ Both interfaces may serve at the same time. Both respond to simple text command,
     - `nice-ratio=0.5` will cause `gh-ost` to sleep for `50ms` immediately following.
     - `nice-ratio=1` will cause `gh-ost` to sleep for `100ms`, effectively doubling runtime
     - value of `2` will effectively triple the runtime; etc.
+- `throttle-http`: change throttle HTTP endpoint
 - `throttle-query`: change throttle query
 - `throttle-control-replicas='replica1,replica2'`: change list of throttle-control replicas, these are replicas `gh-ost` will check. This takes a comma separated list of replica's to check and replaces the previous list.
 - `throttle`: force migration suspend