docs: update bugs and limitations document

docs/content/bugs.md

@@ -1,31 +1,42 @@
 ---
 title: "Bugs"
 description: "Rclone Bugs and Limitations"
-date: "2014-06-16"
+date: "2019-08-04"
 ---
 
-Bugs and Limitations
---------------------
+# Bugs and Limitations
 
-### Empty directories are left behind / not created ##
+## Limitations
 
-With remotes that have a concept of directory, eg Local and Drive,
-empty directories may be left behind, or not created when one was
-expected.
+### Directory timestamps aren't preserved
 
-This is because rclone doesn't have a concept of a directory - it only
-works on objects.  Most of the object storage systems can't actually
-store a directory so there is nowhere for rclone to store anything
-about directories.
+Rclone doesn't currently preserve the timestamps of directories.  This
+is because rclone only really considers objects when syncing.
 
-You can work round this to some extent with the`purge` command which
-will delete everything under the path, **inluding** empty directories.
+### Rclone struggles with millions of files in a directory
 
-This may be fixed at some point in
-[Issue #100](https://github.com/rclone/rclone/issues/100)
+Currently rclone loads each directory entirely into memory before
+using it.  Since each Rclone object takes 0.5k-1k of memory this can
+take a very long time and use an extremely large amount of memory.
 
-### Directory timestamps aren't preserved ##
+Millions of files in a directory tend caused by software writing cloud
+storage (eg S3 buckets).
+
+### Bucket based remotes and folders
+
+Bucket based remotes (eg S3/GCS/Swift/B2) do not have a concept of
+directories.  Rclone therefore cannot create directories in them which
+means that empty directories on a bucket based remote will tend to
+disappear.
+
+Some software creates empty keys ending in `/` as directory markers.
+Rclone doesn't do this as it potentially creates more objects and
+costs more.  It may do in future (probably with a flag).
+
+## Bugs
+
+Bugs are stored in rclone's Github project:
+
+* [Reported bugs](https://github.com/rclone/rclone/issues?q=is%3Aopen+is%3Aissue+label%3Abug)
+* [Known issues](https://github.com/rclone/rclone/issues?q=is%3Aopen+is%3Aissue+milestone%3A%22Known+Problem%22)
 
-For the same reason as the above, rclone doesn't have a concept of a
-directory - it only works on objects, therefore it can't preserve the
-timestamps of directories.