[GitHub] [couchdb-documentation] davisp commented on a change in pull request #410: add rfc for map indexes

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davisp commented on a change in pull request #410: add rfc for map indexes
URL: https://github.com/apache/couchdb-documentation/pull/410#discussion_r283464151
 
 

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 File path: rfcs/008-map-indexes.md
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+# Map indexes RFC
+
+---
+name: Formal RFC
+about: Submit a formal Request For Comments for consideration by the team.
+title: ‘Map indexes on FoundationDB’
+labels: rfc, discussion
+assignees: ''
+
+---
+
+## Introduction
+
+This document describes the data model and index management for building and querying map indexes.
+
+## Abstract
+
+Map indexes will have their own data model stored in FoundationDB. The model includes grouping map indexes via their design doc's view signature. Each index will have the index key/value pairs stored, along with the last sequence number from the changes feed used to update the index.
+
+Indexes will use the changes feed and be updated via the background tasks queue. If the index only needs a very small update, the update can happen in the request instead of via the background job queue.
+
+There will be new size limitations on keys (10KB) and values (100KB) that are emitted from a map function.
+
+## Requirements Language
+
+[NOTE]: # ( Do not alter the section below. Follow its instructions. )
+
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+"SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
+document are to be interpreted as described in
+[RFC 2119](https://www.rfc-editor.org/rfc/rfc2119.txt).
+
+## Terminology
+
+`Sequence`: a 13 byte value formed by combining the current `Incarnation` of the database and the `Versionstamp` of the transaction. Sequences are monotonically increasing even when a database is relocated across FoundationDB clusters. See (RFC002)[LINK TBD]  for a full explanation.
+
+`View Signature`:  A md5 hash of the views, options, view language defined in a design document.
+
+---
+
+## Detailed Description
+
+CouchDB views are used to create secondary indexes for the documents stored in a CouchDB database. An index is defined by creating a map/reduce functions in a design document. This document describes building the map indexes on top of FoundationDB (FDB).
+
+### Data model
+
+A map index is created via a design document, an example is shown below:
+
+```json
+{
+  "_id": "_design/design-doc-id",
+  "_rev": "1-8d361a23b4cb8e213f0868ea3d2742c2",
+  "views": {
+    "map-view": {
+      "map": "function (doc) {\n  emit(doc._id, 1);\n}"
+    }
+  },
+  "language": "javascript"
+}
+```
+
+The view’s map function will be used to generate keys and values which will be stored in FDB as the secondary index. Format for storing the key/values is:
+
+```json
+{<database>, ?VIEWS, <view_signature>, ?VIEWS, <view_id>, ?MAP, <keys>, <_id>} -> <emitted_value>
+```
+
+Where each field is defined as:
+
+* `<database>` is the specific database namespace
+* `?VIEWS` is the standard views namespace.
+* `view_signature` is the design documents `View Signature`
+* `view_id` name of a view defined in the design document
+* `?MAP` is the standard map namespace
+* `keys` are the emitted keys from the map function
 
 Review comment:
   The plurality of `keys` here is confusing to me. Certainly you mean that there's a row per key emitted?

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