[couchdb] 01/02: update README

[ja...@apache.org]

This is an automated email from the ASF dual-hosted git repository.

jan pushed a commit to branch 749-fix-couch_peruser-app-structure
in repository https://gitbox.apache.org/repos/asf/couchdb.git

commit 697ab2dcd30f8d73eea93bcafb9c1ed74f7fb9d7
Author: Jan Lehnardt <ja...@apache.org>
AuthorDate: Mon Oct 9 08:45:44 2017 +0200

    update README
---
 src/couch_peruser/README.md | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/couch_peruser/README.md b/src/couch_peruser/README.md
index 70f8348..64a0518 100644
--- a/src/couch_peruser/README.md
+++ b/src/couch_peruser/README.md
@@ -1,6 +1,6 @@
 # couch_peruser [![Build Status](https://travis-ci.org/apache/couchdb-peruser.svg?branch=master)](https://travis-ci.org/apache/couchdb-peruser)
 
-couch_peruser is a CouchDB daemon that ensures that a private per-user
+couch_peruser is a CouchDB application that ensures that a private per-user
 database exists for each document in _users. These databases are
 writable only by the corresponding user. Databases are in the form:
 
@@ -15,3 +15,20 @@ correctly implement in just about any language, especially JavaScript
 and Erlang. Other encodings would be possible, but would require
 additional client and server-side code to support that encoding. This
 is the simplest scheme that is obviously correct.
+
+## Implementation Notes
+
+The module itself is a `gen_server` and it implements the `mem3_cluster`
+behaviour.
+
+In a CouchDB cluster, the module runs on each node in the cluster. On startup,
+it launches a changes listener for each shard of the `authentication_db`
+(`_users`).
+
+In a cluster, when a change notification comes in (after a user doc has been
+created/updated/deleted), each node independently calculates if it should
+handle the notification based on the current list of active nodes in the
+cluster. This ensures that we avoid trying to update the internal `_dbs`
+concurrently and causing conflicts. It also ensures that at least one node
+does handle a notification. The mechanism that handles this does survive
+cluster reconfigurations transparently.

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