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Short Description
RTDB is a real-time database implemented in Node.js.
Full Description

rtdb

© 2016 by Rheosoft. All rights reserved.
Licensed under the RTDB Software License version 1.0.

Comments, questions? info@rheosoft.com

Overview

rtdb is a real-time JSON document database.
Data is made available via map/reduce queries.
Queries are updated in real-time and subscribers are notified instantly as data is added.

The open source version of rtdb takes big data principles and extends into the practical domain.
The map/reduce construct is applied for real-time data to provide a unique, live analytical view of data.

Use rtdb and leave polling behind!

Installing

Usage

Launch rtdb with node.js. Application settings are supplied via json.

node rtdb.js --settings settings/settings.json

PaaS sites

Online demo versions of rtdb are available.

https://rtdb.herokuapp.com

https://rtdb-rheosoft.rhcloud.com

https://rtdb.mybluemix.net

Acknowledgements

rtdb was inspired by and indebted to several projects.

Especially couchdb and node.js.

Thanks to npm and several excellent libraries. See package.json for more details.

Some samples contain a freely licensed template from MediaLoot.

Web interface

When running locally, the main web interface is reachable at

http://localhost:9001/web/

The web interface provides the ability to manage collections, views and subscriptions.

Architecture

Documents

rtdb is a document-oriented database. A document may be any JSON object.

Collections

Documents are organized into "Collections". A collection is a specific type of document. There is no requirement that all documents
be the same JSON format but it does help somewhat that all documents in a given collection have similar structures when designing queries.

Views

Each collection contains "Views". A View represents a particular query into the Collection. All queries must be "pre-registered".
There is no "ad-hoc" query facility. However, as the data changes, registered queries are run continuously and subscribers are updated in real-time.

Subscriber

A "Subscriber" represents a party (usually a browser) interested in receiving updates when the query results change. A query may have many subscribers.
Subscribers are registered via HTML EventSources.

The hierarchy is straightforward.

Collections → Views → Subscribers
↳ Documents

Map/Reduce

The query within each view is implemented via map/reduce. Each query requires a map function and a reduce function.
Optionally, a finalize function and a personalize function can be added.
For incoming documents, the pipeline follows this pattern.

Map → Reduce → Finalize → Personalize

Map

The map function is called once for each incoming document. The purpose is to initially categorize the data
and it takes the following arguments.

  • item - item is the document to process.
  • emit - emit is a function that is called to map the item.
  • database - a reference to the database for accessing other collections/views.

emit takes two arguments.

* key - the hash to store
* value - the value to store

emit may be called one or more times for each call to map.

Reduce

Reduce is called once for each key emitted by map. It takes the following arguments.

  • values - an array of values to reduce
  • rereduce - a boolean indicating if we are rereducing.
  • emit - a function that is called to emit the result.
  • database - a reference to the database for accessing other collections/views.

emit takes one argument, the result of the reduction.
emit should be called no more than once per reduce.

rtdb uses the re-reduce approach to accomplish incremental map/reduce. The reduce function you supply must honor this flag.

"[A] Reduce function has the requirement that not only must it be referentially transparent,
but it must also be commutative and associative for the array value input,
to be able reduce on its own output and get the same answer."

Damien Katz

Therefore, again citing Damien, for a reduce function,

 f(Key, Values) == f(Key, [ f(Key, Values) ] )

More discussion here.

Finalize

The finalize function may be used to sort and/or cull the result set before sending to subscribers.
A common usage would be to sort and trim to a "top 10" list.

finalize takes the following arguments.

  • reduction - an array of reduced values to finalize.
  • emit - a function that is called to emit the result. Pass the finalized reduction.
  • database - a reference to the database for accessing other collections/views.

Personalize.

The personalize function is similar to finalize however is it called individually for each subscriber.
The intent is to allow the function to use HTTP header values to identify the subscriber and personalize the result set
specifically for the subscriber. A common usage pattern would be to filter the data based on the user.

personalize takes the following arguments.

  • reduction - an array of reduced values to finalize.
  • headers - the HTTP headers of the current subscriber. See node.js documentation.
  • emit - a function that is called to emit the result. Pass the personalized reduction.
  • database - a reference to the database for accessing other collections/views.

Since personalize is called for each subscriber, consider the scalability of this feature as your user base grows.

Security

rtdb has limited inherent security. This is by design.

rtdb is intended to be run behind a secure web server such as Apache.
Apache and other web servers provide secure facilities applying granular, URL based security to rtdb.
See advanced topic, securing rtdb.

"Out of the box", rtdb implements Basic Authentication security for the administration functions.
The user/password are set via environmental variables RTDBADMIN_USER and RTDBADMIN_PWD.
In a production environment where security has been delegated, the Basic Authentication may be disabled
by changing the settings json parameter disableBasicAuth to true.

If rtdb is used over the internet, be sure to secure the traffic with https if you intend to rely on basic authentication.

REST API

rtdb uses a simple REST API to manage and interact with the database. (The web interface even uses this REST API behind the scenes.
Feel free to check out the HTML!)

The REST API speaks JSON and uses standard verbs.

GET - return a JSON object.
PUT - update passing a JSON object.
DELETE - delete object according to url.
POST - insert JSON object or execute command according to URL.

Each collection, view and subscriber is given a Globally Unique Identifier (GUID).
Using a GUID guarantees uniqueness of the individual objects and allows separate databases to be combined if needed.
The GUID is used to reference specific objects via the REST API.

The web interface is an easy way to familiarize yourself with the GUIDs.

Operations on Collections

POST /db/collections - Add a new Collection.
PUT /db/collections/[col_guid] - Update Collection.
DELETE /db/collections/[col_guid] - Delete Collection.
GET /db/collections - List all collections.
GET /db/collections/[col_guid] - List specific collection.
POST /db/collections[col_guid]/documents - Add a Document or Array of Documents.
DELETE /db/collections/[col_guid]/documents - Delete all Documents.

Operations on Views

POST /db/collections[col_guid]/views - Add a new View.
PUT /db/collections/[col_guid]/views/[view_guid] - Update View.
DELETE /db/collections/[col_guid]/views/[view_guid] - Delete View.
GET /db/collections/[col_guid]/views - List all Views.
GET /db/collections/[col_guid]/views/[view_guid] - List View.
GET /db/collections/[col_guid]/views/[view_guid]/ticket - fetch security ticket.
GET /db/collections/[col_guid]/views/[view_guid]/subscribers - List subscribers.
GET /db/collections/[col_guid]/views/[view_guid]/reduction - List query result.

Miscellaneous Operations

GET /db/stream?view=[guid] - Used by EventSource. Multiple view params are supported.
GET /db/admin/stats - Show database stats in JSON.
POST /db/admin/stop - Shutdown the database.

Using rtdb

Steps for using rtdb are:

  1. Use the web interface or REST API to create a collection.
  2. Create one or more views for the collection.
  3. Subscribers register via WebSocket or Server Sent Event API.
  4. Insert new JSON documents via the REST API.
  5. Subscribers receive updates as documents are inserted.

Use the REST API to insert documents. An example CURL syntax to load a file mydoc.json would be

curl -X POST -H 'Content-Type: application/json' -d @mydoc.json http://localhost:9001/db/collections/[col_guid]/documents

Note that for inserts, the rtdb REST API expects either a single JSON document or array of documents.
To maximize performance, the map/reduce is run once for the entire array.
So use arrays when inserting multiple documents at once.

Subscribers, often a web browser application, register for streams via the HTML5 event source API or WebSockets.

Server Sent Events (EventSources)

EventSources provide a mechanism for the database to push updates to subscribers (usually a browser).
This eliminates the need for clients to poll the database, checking for updates.

The heart of rtdb is the ability to send aggregations to subscribers in real-time.

Often a browser client may want to show multiple views on a single page. Intuitively, you may create an EventSource
for each interesting view. However in practice, web browsers
limit the number of active EventSources to a very small number.
Instead of creating multiple EventSources, rtdb allows you to supply a list of views when registering a single
EventSource. With this technique there is no browser imposed limit to the number of subscriptions.

When adding the EventListener, pass the GUID of each view as a param. Here we register two views.

var source = new EventSource(
    "/db/stream?view=6f57030d-ccad-41df-aa92-689292fa2c42&view=ec537999-60a5-41f3-9036-fcd3d5356ae2");

source.addEventListener("6f57030d-ccad-41df-aa92-689292fa2c42", function(event) {
    console.log(event.data);
    }, false);

source.addEventListener("ec537999-60a5-41f3-9036-fcd3d5356ae2", function(event) {
    console.log(event.data);
    }, false);

Securing Subscriptions

rtdb provides a ticket based security model. ACL based security is enabled via the settings.json by setting
useACLTicket to true. In this case, a ticket must first be retrieved for each view via a REST call.

/db/collections/[col_id]/views/[view_guid]/ticket

The "ticket" provides the proper authorization to initiate the subscription. This pattern is in place so that an upstream
ACL security mechanism can check the URL and do the authentication.
Since collections and views have unique GUIDs, access to the resource
can be secured at a quite granular level.

Tickets are passed to the EventSource as a param. If more than one view is required, pass multiple view and ticket params.

var source = new EventSource(
    "/db/stream?view=6f57030d-ccad-41df-aa92-689292fa2c42&ticket=" + ticket);

The ticket has a short expiration (less than one minute) so that it may not be cached or passed around.
It should be used once,
immediately after requesting it.

WebSockets

Subscriber data only flows in a single direction in rtdb. Therefore Server Sent Events are
an excellent choice for a transport. It is more widely supported in PaaS environments and may behave better with proxies.
However, in some cases, WebSockets are preferable and may even be required to support certain browsers such as Internet
Explorer.

rtdb uses the excellent socket.io package for WebSocket support. The connection steps are as follows:

First secure a ticket for the view or views if ACL security is enabled. This process is identical to using Server Sent Events.

Once the ticket is secured, the socket is created.

var view, var ticket; 
var socket = io.connect(); 

In the socket connect event, we use emit to call the server and "subscribe" to the view, passing the ticket.
If you are subscribing to multiple views, pass an array of view/ticket JSON objects.

socket.on('connect', function () {
  socket.emit('subscribe', { ticket: ticket, view: view });

  socket.on(view,
     function(data) {
     ...do something with data...
     }
     );
  });

The demos discussed below serve as references for a complete implementation.

Demos

rtdb comes with two sample collections and a web front-end accessible at

http://localhost:9001/demo/apples

http://localhost:9001/demo/parcels

These two demos utilize Server Sent Events to receive real-time updates. Documents are added through the REST API.

The "Apples" demo provides a simple front end for adding new documents and viewing the aggregations.
It is more interesting when running simultaneously on multiple browsers.

The "Parcels" demo uses a small sample of public domain property tax parcel data and inserts documents
repeatedly to provide constantly updating aggregations. The inserts are initiated by cfs/parcels.js.
Be sure to remove or move this file in a production environment.

Note that an online connection is required to load the Google libraries used for charting.

Also included are mobile versions of the demos. Accessible via the navigation menu or loaded by default
if accessing the demo from a mobile platform.

Websocket Demos

Additional samples have been provided illustrating Websocket support.

http://localhost:9001/demo/applesws

http://localhost:9001/demo/parcelsws

Advanced Topics

rtdb files and directories

Here is a summary of the rtdb project file structure.

 /package.json - packaging file for NPM  
 /README.md - this file   
 /rtdb.js - the main class  
 /collection.js - collection class  
 /identity.js - helper class for guid identity  
 /view.js - view class  
 /db.js - database class
 /license.pdf - the license  
 /cfs - the pluggable file systems  
     /cfslocal.js - local file storage  
     /cfss3.js - Amazon S3 storage  
     /parcels.js - loader for parcel demo. 
 node_modules - required Node modules installed by NPM
 /public - static files served by the web server  
 /settings - startup options in JSON format  
    /settings.json - basic settings  
    /mocha.json - settings for running mocha tests  
 /test - mocha tests  
 /views - Jade templates used by the web interface
 /sampledb - the sample collections used by the demos  

There are two default settings files in /settings

settings.json - a basic startup settings file. It will run the demo database provided
in the sampledb subdirectory.
mocha.json - used for mocha testing.
Note, to run all the mocha tests successfully, you will need to provide valid S3 connection params in this file.

Database file structure

The database is a hierarchy of JSON files. Each JSON file is uniquely named [guid].json.
Where [guid] is the GUID assigned to the object.

/collections - contains one file for each collection in format [col_guid].json
/collection/[col_guid]/documents - contains one json file per document.
/collection/[col_guid]/views - contains one file for each view in format [view_guid].json
/collection/[col_guid]/view/[view_guid]/reduction - for "transient" collections, each reduction is saved at shutdown.

Securing rtdb

rtdb is designed to work with standard web-based security mechanisms.

User and group authentication should be considered for any production deployment.

The REST API may be secured by specific URL to limit or control access at the collection or view level.

In production environments, admin functions should be secured by HTTP method and URL.

Collection attributes

There are several attributes on a collection worth mentioning.

Document Expirations

A collection may be given an document expiration in milliseconds.
This can be useful for implementing queries based on sliding windows. (i.e. trends for the last hour, last day, etc).
If you only want the last hour's worth of data, set the expiration to 3600000.
The views associated with the collection will be automatically map/reduced when the expiration is triggered.

Note, the expiration value is used to signal when to map/reduce.
It is expected that the persistence provider perform the actual removal of the stale documents.
In the case of the local filesystem CFS, an external task, such as a cron entry, should be used to delete stale files.

To illustrate the sequence, here is an example.

10:05am - insert 5 documents; assume expiration is 3660 secs. (1 hour + 1 minute)
10:15am - insert 5 more documents
11:05am - cron runs, deleting all files older than 60 mins.
11:06am - expiration timer will fire; collection will be map/reduced. Initial documents added at 10:05 will have fallen off.

Using expiration can be expensive. As each batch of documents expires, the full collection must be map-reduced.
But Expiration will ensure the collection is map-reduced the minimum number of times required.
If you are inserting large volumes of documents, consider forcing a map-reduce via the REST API on a regular interval instead.

If you are concerned about the expense of performing a full map-reduce on a frequent basis,
consider clearing the collection on a timed interval.
The effect is a bit different than a sliding window, but very efficient.

Using Transient

When a collection is marked as transient, collections are reduced, but documents are not persisted.
This can be useful for high volume or when the data is persisted elsewhere.

One caveat is that when views are added or updated, the reduction can only happen on "new" documents.

Reductions are persisted when the database is shutdown so that current state of reductions are preserved when the database is restarted.

Note that collections that use expiration cannot use transient.
These two flags are mutually exclusive.

Using Priority

When a collection will be used for lookups (aka master tables), it must be loaded before its dependent collections.
Use the Priority to order how collections are loaded. Lower numbers are loaded first. Find further discussion
below on referencing other collections from within a query.

Using Deltas

Often the amount of data that changes between events is small compared to the overall size of the reduction.
RTDB offers a form of compression for this case and sends just the difference between the last reduction and latest one.

This mode is enabled by passing the query parm delta when subscribing to a stream. i.e.

/db/stream?view=6f57030d-ccad-41df-aa92-689292fa2c42&delta=true

Or in the case of a WebSocket, send

delta: true

in the subscription event.

In delta mode rtdb will initially send a full JSON reduction, then all subsequent updates will be diffs.
The symmetry Javascript library may be used to patch the reduction with the latest diff.

var reduction = Symmetry.patch(lastreduction,JSON.parse(event.data));  

A delta version of the demo may be found here.

Use delta mode when the overall size of the reduction is large compared to the amount of incremental change.
However, depending on the view, using delta mode may be less efficient than sending the full reduction.

Referencing other Collections in a Query

Unlike a relational database, there is no join syntax to combine collections.
However the global database object is passed to the map/reduce methods and
this can be useful for referencing other collections when a lookup is required.
You will need to provide a "lookup" reduction on the collection containing the master data.

// myobject will contain the key used for the lookup
var myobject;
// Use a GUID to get a reference to the collection containing master data
var c=database.collectionAt('be2aec31-3d1d-4674-bc20-106d5c46e220'); 
// Use a GUID to get the intended view
var v = c.viewAt('e3ef472a-1f7e-469e-98f9-cf759cc05352'); 
// do the lookup by using "myobject" as the hash
var r = v.reductionAt(myobject);
// use the return value "r" as needed.

IPv6

rtdb supports IPv6. Supply an IPv6 listen address for the hosts param in the settings json.

"hosts": ["::1"]

This field takes an array so you may supply both an IPv4 address and IPv6 if desired.

"hosts": ["::1","localhost"]

If you wish to use the parcels demo with IPv6, you will also need to update the hosts value in parcels.js.

Settings

The settings json file is the mechanism to supply database parameters.

hosts: an array of hosts to listen on. May be IPv4 or IPv6.
port: The port to listen on.
useACLTicket: boolean to enable the ACL/ticket security mechanism.
disableBasicAuth: boolean to disable basic authentication for DB admin functions.
cfs: the persistence layer to use.
cfsinit: json object passed to persistence layer for initialization params.
reduceInterval: minimum interval between subscriber updates.
expirationInterval: expiration interval for transient collections.

Jade

The excellent Jade templating engine is used for the web administration and the demos.
The templates are contained in the /views subdirectory. Templates may be added or modified dynamically.
(i.e. no need to restart rtdb.)

Licensing

rtdb is licensed under the RTDB Software License version 1.0.
Commercial licenses and support are also available @info@rheosoft.com.

Custom Persistence

rtdb uses a plugin architecture for persistence. A local filesystem (cfslocal) implementation and Amazon S3 (cfss3) are provided.
To add your own provider, implement the following methods for your provider and install
the javascript module into the /cfs subdirectory.
Use either cfslocal.js or cfss3.js as a template.

function name()  - return a unique name for this provider
function init(parms)  - initialize with params from settings.json
function exists(dir, callback)  - does this exist? 
function get(key, callback)  - return object by key
function del(key, callback)   - delete object by key
function put(prefix, item, callback, expires)   - put object
function list(prefix, callback)  - list objects

cfslocal

cfslocal is the default persistence layer. Database objects are writen to the local file system.
The cfslocal persistence layer takes a single initialization param.

"root" : "sampledb/"

Set this value to to the location of the local directory to contain the database files.

cfss3

cfss3 allows writing to the Amazon S3 file system. Supply your credentials accordingly in the settings json.

"config" : { "accessKeyId" : "xxx", 
    "secretAccessKey": "xxx", 
    "region": "us-east-1" 
        },
"params" : {
    "Bucket" : "xxxxxx"
    }


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