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new 938a8e4 Fix ambiguity in documentation on shards and replicas (#338)
938a8e4 is described below
commit 938a8e46b8f3b68bbf9d6104dcc4dbafb60825c1
Author: Adrien Vergé <[email protected]>
AuthorDate: Fri Oct 12 01:45:13 2018 +0200
Fix ambiguity in documentation on shards and replicas (#338)
---
src/cluster/theory.rst | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/src/cluster/theory.rst b/src/cluster/theory.rst
index e92bd6b..ca54d6b 100644
--- a/src/cluster/theory.rst
+++ b/src/cluster/theory.rst
@@ -50,9 +50,15 @@ set using the w parameter. If fewer than this number of
nodes is available, a
We will focus on the shards and replicas for now.
-A shard is a part of a database. The more shards, the more you can scale out.
-If you have 4 shards, that means that you can have at most 4 nodes. With one
-shard you can have only one node, just as with CouchDB 1.x.
+A shard is a part of a database. It can be replicated multiple times. The more
+copies of a shard, the more you can scale out. If you have 4 replicas, that
+means that all 4 copies of this specific shard will live on at most 4 nodes.
+With one replica you can have only one node, just as with CouchDB 1.x.
+No node can have more than one copy of each shard replica. The default for
+CouchDB since 2.0.0 is ``q=8`` and ``n=3``, meaning each database (and
secondary
+index) is split into 8 shards, with 3 replicas per shard, for a total of 24
+shard replica files. For a CouchDB cluster only hosting a single database with
+these default values, a maximum of 24 nodes can be used to scale horizontally.
Replicas add failure resistance, as some nodes can be offline without
everything
crashing down.
