assume-rbr and SUPER documentation

- introducing --assume-rbr
- discussing the implication of being able to run without SUPER

doc/command-line-flags.md

@@ -16,6 +16,12 @@ When your migration issues a column rename (`change column old_name new_name ...
 
 If you think `gh-ost` is mistaken and that there's actually no _rename_ involved, you may pass `--skip-renamed-columns` instead. This will cause `gh-ost` to disassociate the column values; data will not be copied between those columns.
 
+### assume-rbr
+
+If you happen to _know_ your servers use RBR (Row Based Replication, i.e. `binlog_format=ROW`), you may specify `--assume-rbr`. This skips a verification step where `gh-ost` would issue a `STOP SLAVE; START SLAVE`.
+Skipping this step means `gh-ost` would not need the `SUPER` privilege in order to operate.
+You may want to use this on Amazon RDS
+
 ### conf
 
 `--conf=/path/to/my.cnf`: file where credentials are specified. Should be in (or contain) the following format:

doc/requirements-and-limitations.md

@@ -7,7 +7,15 @@
 - `gh-ost` requires an account with these privileges:
 
   - `ALTER, CREATE, DELETE, DROP, INDEX, INSERT, LOCK TABLES, SELECT, TRIGGER, UPDATE` on the database (schema) where your migrated table is, or of course on `*.*`
-  - `SUPER, REPLICATION SLAVE` on `*.*`
+  - either:
+    - `SUPER, REPLICATION SLAVE` on `*.*`, or:
+    - `REPLICATION CLIENT, REPLICATION SLAVE` on `*.*`
+
+The `SUPER` privilege is required for `STOP SLAVE`, `START SLAVE` operations. These are used on:
+
+- Switching your `binlog_format` to `ROW`, in the case where it is _not_ `ROW` and you explicitly specified `--switch-to-rbr`
+  - If your replication is already in RBR (`binlog_format=ROW`) you can specify `--assume-rbr` to avoid the `STOP SLAVE/START SLAVE` operations, hence no need for `SUPER`.
+- Running `--test-on-replica`: before the cut-over phase, `gh-ost` stops replication so that you can compare the two tables and satisfy that the migration is sound.
 
 ### Limitations
 
@@ -20,6 +28,7 @@
   - `gh-ost` will do its best to pick a migration key with non-nullable columns. It will by default refuse a migration where the only possible `UNIQUE KEY` includes nullable-columns. You may override this refusal via `--allow-nullable-unique-key` but **you must** be sure there are no actual `NULL` values in those columns. Such `NULL` values would cause a data integrity problem and potentially a corrupted migration.
 - It is not allowed to migrate a table where another table exists with same name and different upper/lower case.
   - For example, you may not migrate `MyTable` if another table called `MYtable` exists in the same schema.
-- Amazon RDS and Google Cloud SQL are probably not supported (due to `SUPER` requirement)
+- Amazon RDS and Google Cloud SQL are currently not supported
+  - We began working towards removing this limitation. See tracking issue: https://github.com/github/gh-ost/issues/163
 - Multisource is not supported when migrating via replica. It _should_ work (but never tested) when connecting directly to master (`--allow-on-master`)
 - Master-master setup is only supported in active-passive setup. Active-active (where table is being written to on both masters concurrently) is unsupported. It may be supported in the future.

doc/testing-on-replica.md

@@ -63,3 +63,6 @@ $ gh-osc --host=myhost.com --conf=/etc/gh-ost.cnf --database=test --table=sample
 ### Further notes
 
 Do not confuse `--test-on-replica` with `--migrate-on-replica`; the latter performs the migration and _keeps it that way_ (does not revert the table swap nor stops replication)
+
+As part of testing on replica, `gh-ost` issues a `STOP SLAVE`. This requires the `SUPER` privilege.
+See related discussion on https://github.com/github/gh-ost/issues/162