wohali commented on a change in pull request #268: Rewrite sharding documentation URL: https://github.com/apache/couchdb-documentation/pull/268#discussion_r179878729
########## File path: src/cluster/sharding.rst ########## @@ -18,43 +18,170 @@ Sharding .. _cluster/sharding/scaling-out: -Scaling out -=========== +Introduction +------------ -Normally you start small and grow over time. In the beginning you might do just -fine with one node, but as your data and number of clients grows, you need to -scale out. +A +`shard <https://en.wikipedia.org/wiki/Shard_(database_architecture)>`__ +is a horizontal partition of data in a database. Partitioning data into +shards and distributing copies of each shard (called "replicas") to +different nodes in a cluster gives the data greater durability against +node loss. CouchDB clusters automatically shard and distribute data +among nodes, but modifying cluster membership and customizing shard +behavior must be done manually. -For simplicity we will start fresh and small. +Shards and Replicas +~~~~~~~~~~~~~~~~~~~ -Start ``node1`` and add a database to it. To keep it simple we will have 2 -shards and no replicas. +How many shards and replicas each database has can be set at the global +level, or on a per-database basis. The relevant parameters are *q* and +*n*. -.. code-block:: bash +*q* is the number of database shards to maintain. *n* is the number of +copies of each document to distribute. With q=8, the database is split +into 8 shards. With n=3, the cluster distributes three replicas of each +shard. Altogether, that's 24 shards for a single database. In a default +3-node cluster, each node would receive 8 shards. In a 4-node cluster, +each node would receive 6 shards. Review comment: Maybe a sentence here about why we recommend that the number of nodes in a cluster be divisible by 3? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
