ewd-memory-globals: Memory emulation of Global Storage database

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Special thanks to the Ripple Foundation http://rippleosi.org for support and funding of this project.

ewd-memory-globals

This module provides an emulation of a Global Storage database using memory storage.

The APIs are modelled on the cache.node interface provided by the Caché database (a proprietary Global Storage database) and are designed to behave identically.

It is designed to be used in conjunction with the ewd-qoper8 module and used within its worker processes, where synchronous database access does not interfere with the main Node.js process, rather than in conventional Node.js-based applications.

See https://robtweed.wordpress.com/2016/03/03/higher-level-database-operations-with-node-js/ for further background.

APIs

The following APIs are provided:

open()
close()
get()
set()
data()
increment()
kill()
next()
previous()
next_node()
previous_node()
lock()
unlock()
global_directory()
version()

Examples

Several examples demonstrating the use of ewd-memory-globals are included in the /examples folder.

In addition to basic API tests, you can also see how the ewd-document-store module provides a high-level abstraction of ewd-memory-global's Global Storage as:

• persistent JavaScript Objects
• document database

See /examples/docstore-tests.js

For more information on ewd-document-store, see:

http://gradvs1.mgateway.com/download/ewd-document-store.pdf

You'll also find a detailed set of presentations on Global Storage databases and the ewd-document-store JavaScript abstraction on the M/Gateway Web Site: go to:

  [http://www.mgateway.com](http://www.mgateway.com)

Click the Training tab. Parts 17 to 27 will provide in-depth background. ewd-memory-globals will behave identically to the other Global Storage databases referred to in these presentations.

How Global Storage is Emulated in ewd-memory-globals

To understand the basics of a Global Storage database, see

http://www.slideshare.net/robtweed/ewd-3-training-course-part-17-introduction-to-global-storage-databases

The hierarchical structure of a Global is emulated using plain JavaScript object

• node:xxxx A hash that contains details about each Global Node, specifically whether it's a leaf-node or not, and if so, its value
• children:xxxx A sorted list containing any child subscript values for each of a Global's nodes
• leaves:xxxx A sorted list containing pointers to the node: keys for leaf nodes only

A global node key (xxxx) is constructed from the Global name and its Subscripts. They are flattened into a singe string using Hex 01 as a delimiter. For example the Global Node:

  rob("a","b","c")

would be represented as:

  rob\x01a\x01b\x01\c

In order to emulate the subscript collating order of Global Storage database, integer subscript values are padded out with up to 9 leading zeros within the children:xxxx sorted lists.

The Lock and Unlock commands are emulated using the Redis Blocking Pop command BLPOP and use two additional simple keys:

• lock:xxxx Representing the Global Node that is locked
• locker: xxxx Representing the process locking the node

License

The MIT License (MIT)

Copyright (c) Alexey Kucherenko

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.