Does Ripple use an RDBMS? If so, which one?


If they're in the same order book (same currency/issuer pairs), it's the one that was placed first.

If they're in different order books (say because the source holds balances from more than one issuer) it's a bit more complex. Even if the offer rates are the same, the effective rate might not be the same. For example, if one issuer has a higher transfer fee, that can make the effective rate higher even if the offer rate is the same.

If the effective rate is the same, then it's the one specified first in the transaction's path set. Currently, the server sorts the path set when the transaction is formed based on an attempt to provide the most liquidity and any benefits that can be achieved. So, for example, if one path reduces a balance that's over its limit, that will be...

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1. What is Ripple?

Ripple is the name for both a digital currency (XRP) and an open payment network within which that currency is transferred. It is a distributed, open-source payments system that’s still in beta. The goal of the ripple system, according to its website, is to enable people to break free of the “walled gardens” of financial networks – ie, credit cards, banks, PayPal and other institutions that restrict access with fees, charges for currency exchanges and processing delays.

2. What does Ripple do?

According to is OpenCoin, the company behind ripple, the currency addresses the need to keep money flowing freely. A company blog post titled “Ripple and the Purpose of Money” gives a brief history of money and its transportability, and points to the frustration of having banks and other institutions impede the transfer of funds with transaction fees and processing delays. The goal of Ripple, it says, is to build on the decentralized digital currency...

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This is a technical overview of the Ripple payment system.

At its heart, Ripple is a distributed database. One of Ripple's goals is to provide distributed database services that other applications can build on top of. The first such application is the Ripple payment system.

The Ledger

The collection of information that comprises the state of the database is called the Ledger. Every few seconds a new version of the ledger computed. A ledger that is known to be accurate is considered validated.

Each version of the ledger has a hash which identifies it and contains the hash of the previous ledger. The implication is that once the hash of the current ledger is validated, all prior ledgers in the chain are also validated.

The ledger is a combination Radix tree and Merkle tree. This combination allows Ripple to quickly determine the differences between a local ledger and a remote ledger. Using this difference information ledgers can be quickly...

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What does "ripple current" mean?

It always bugs me whenever I think about it. I know that the definition (from panasonic website):

Ripple Current
Ripple current is the rms value of alternating current flowing through a capacitor. This current causes an internal temperature rise due to power losses within the capacitor.

ESR (Equivalent Series Resistance)
Equivalent series resistance causes heat generation within the capacitor when AC ripple current flows through the capacitor. Maximum ESR is normally specified at 120Hz, 20°C.

So, there is a current flowing through a capacitor, and its value is alternated. The higher the rms value of this ripple current the worse the effect to the capacitor. The internal heat of capacitor will rise as the result of resistance. So this is the use of low esr caps, it's allowed the ripple current flowing through with minimal generated heat in the caps thanks to its low resistance..

The higher the ripple current...

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Register an account
Download ripple server switcher Extract rss.exe somewhere (eg: on your desktop)
Turn off your antivirus (some antiviruses might cause some issues)

Certificate installation

If you want to play on ripple with stable/beta/cutting edge, you must install our HTTPS certificate.
Do this only the first time you connect to Ripple.

Open the switcher
Click on “Install certificate”
Click “Yes”

If you can’t install the certificate properly, follow these instructions to install it manually.

How to play on Ripple

Run the switcher as administrator
Make sure Ripple IP is and Mirror IP is If not, click Update IP to get the right IPs. Make sure that the switcher says “You are playing on Ripple server -” (it should look like this), if not, click “On/Off” to switch server.
Open osu! and login with your ripple account

How to...

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What happens if someone steals all the founders' XRP?

XRP will still be used to pay transaction fees, its critical network function.

Can you spend without a complete ledger?

Yes. You only need the current sequence number of your account.

Can the same wallet be used simultaneously on different computers?

Yes. However, attempts to overspend will fail.

To prevent spamming, transactions require a small transaction fee paid in ripples.

How long before a transaction is considered final?

In ordinary circumstances, a few seconds.

In extraordinary circumstances, this may be as long as several minutes after connectivity is restored.

The client will note when a transaction occurs under extraordinary circumstances. For small transactions and trusted parties, there is no need to wait for connectivity to be restored.

How can a transaction be verified?

The sender specifies a payment address in a...

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Cassandra isn’t a relational database management system, but it has some features that make it look a bit like one. Chief among these is CQL, a query language with an SQL-like syntax. CQL isn’t a bad thing in itself – in fact it’s very convenient – but it can be misleading since it gives developers the illusion that they are working with a familiar data model, when things are really very different under the hood. Not only is Cassandra not an RDBMS, it’s not even like an RDBMS in some of the ways you might expect. In this post I’ll review a few example scenarios where a beginner might be unpleasantly surprised by the differences, and suggest some remedies.

Example 1: querying by non-key columns

Here’s some CQL to create a “shopping trolley contents” table in Cassandra:

CREATE TABLE shoppingTrolleyContents ( trolleyId timeuuid, lineItemId timeuuid, itemId text, qty int, unitPrice decimal, PRIMARY KEY(trolleyId, lineItemId) ) WITH CLUSTERING ORDER BY...
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MongoDB Locking is Different

Locking in MongoDB does not work like locking in an RDBMS, so a bit of explanation is in order. In earlier versions of MongoDB, there was a single global reader/writer latch. Starting with MongoDB 2.2, there is a reader/writer latch for each database.

The readers-writer latch

The latch is multiple-reader, single-writer, and is writer-greedy. This means that:

There can be an unlimited number of simultaneous readers on a database There can only be one writer at a time on any collection in any one database (more on this in a bit) Writers block out readers By "writer-greedy", I mean that once a write request comes in, all readers are blocked until the write completes (more on this later)

Note that I call this a "latch" rather than a "lock". This is because it's lightweight, and in a properly designed schema the write lock is held on the order of a dozen or so microseconds. See here for more on readers-writer locking.


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A ripple edit adjusts a clip’s In or Out point, making the clip longer or shorter, without leaving a gap in the Timeline. The change in the clip’s duration ripples outward, moving all subsequent clips earlier or later in the Timeline. If you don’t use a ripple edit when you change the duration of a clip, you will either leave a gap when you make a clip shorter, or overwrite part of an existing clip if you make a clip longer. Using the Ripple tool is the main way that you perform ripple edits, but you can also select one or more clips in the Timeline and perform a ripple cut or ripple delete. This is when a clip is deleted and all subsequent clips move earlier in the Timeline to fill the gap.

A ripple edit is a one-sided edit, meaning that only an In or Out point of a single clip item is affected. All clips following the shortened or extended clip are moved accordingly in the Timeline, so ripple edits affect both the trimmed clip and the position of all subsequent clips in...

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NoSQL is a hot buzz in the air for a pretty long time (well, it's not only a buzz anymore).

However, when should we really use it?

Best Practices for MongoDB

NoSQL products (and among them MongoDB) should be used to meet challenges. If you have one of the following challenges, you should consider MongoDB:

You Expect a High Write Load

MongoDB by default prefers high insert rate over transaction safety. If you need to load tons of data lines with a low business value for each one, MongoDB should fit. Don't do that with $1M transactions recording or at least in these cases do it with an extra safety.

You need High Availability in an Unreliable Environment (Cloud and Real Life)

Setting replicaSet (set of servers that act as Master-Slaves) is easy and fast. Moreover, recovery from a node (or a data center) failure is instant, safe and automatic

You need...

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This guest post is from Jnan Dash, a tech visionary/executive consultant in Silicon Valley who spent 10 years at Oracle Corporation and 16 years at IBM in various database leadership positions. Dash serves on several boards and advisory boards, including MongoDB's.

By Jnan Dash

The market is abuzz with terms like NoSQL, Big Data, NewSQL, Database Appliance, etc. Often, IT decision makers can get very confused with all the noise. They do not understand why they should consider a newer, alternative database when RDBMSs have been around for 20+ years. However, many leading enterprises are already using alternative databases and are saving money, innovating more quickly, and completing projects they could not pursue before as a result. Let’s discuss how one can determine if NoSQL is a fit for current or future applications.

Nature of data
The first consideration that needs to be made when selecting a database is the characteristics of the data you are...

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Basics of database systems, Traditional file approach, Motivation for database approach, The evolution of database systems, Database basics, Three views of data, The three level architecture of DBMS, Relational database systems, Data models, Database languages, Client-server and multi-tier architectures, Multimedia data, Information integration, Data-definition language commands, Overview of query processing, Storage and buffer management, Transaction processing, The query processor. The Entity-Relationship Data Model, Introduction of entity Relationship model, Elements of the E/R Model, Requirement, Relationship, Entity-Relationship Diagrams, Multiplicity of Binary E/R Relationships, Design Principles, Avoiding Redundancy, Simplicity Counts, Extended ER Models

Representing Data Elements: Data Elements and Fields, Representing Relational Database

Elements, Records, Representing Block and Record Addresses,...

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A database is a collection of data that is stored in an organized manner. This data can either be on a computer or on paper. It is, of course, more efficient to store data on a computer like you can learn in this course, as the computerization of this data makes it easy to retrieve and perform operations on. Today, in the information age, databases of some kind are maintained by all organization, big and small. They are essential in ensuring that the day to day operations of an organization can run smoothly.

An Introduction to Database Systems

There are several software-based products that help you build and maintain databases. These software products are known as database management systems (DBMS). In addition to letting you build a database, most DBMS applications will interact with a user, or multiple users. They will also let you perform operations on the data in their repository. DBMS systems are always based on a computer language (which can vary). A user has...

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Today, change occurs frequently, and data modeling is a huge challenge because of the time and resources that relational databases require. Unfortunately, when using a relational database, even a simple change like adding or replacing a column in a table might be a million dollar task.

From CIOs to developers, everyone is realizing that relational databases were simply not designed for the challenges with today’s data. That’s why there’s been an explosion of data and new database products that have come on the market recently. The list just gets bigger and bigger every year. In fact, this trend has been going on for a number of years now, and the now former CIO of the U.S. Federal Government, Vivek Kundra, even commented on it at a conference back in 2009:

This notion of thinking about data in a structured, relational database is dead.”

In the coming weeks, I am going to write a series of blog posts that explore the key reasons why I believe this...

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An Object-Oriented Database Management System (OODBMS), sometimes referred as Object Database Management System (ODMS) is a Database Management System (DBMS) that supports modeling and creation of data as objects. OODBMS provides support for object classes, class property and method inheritance by sub classes and their objects. A Relational Database Management System (RDBMS) is also a DBMS but, that is based on the relational model. Most popular DBMSs currently in use are RDMSs.

As mentioned earlier RDBMS is based on the relational model and data in a RDMS are stored in the form of related tables. So, a relational database can simply be seen as a collection of one or more relations or tables with columns and rows. Each column corresponds to an attribute of the relation and each row corresponds to a record that consists of data values for an entity. RDMSs are developed by extending hierarchical and the network models, which were two previous...

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The last few weeks I have witnessed a ton of passionate debate about what is better, NoSQL or RDBMS. It almost sounds like a religious battle between Windows and Mac fan-boys. To me this is like arguing that a hammer is better than a screw driver. If you need to pound a nail, I'll take the hammer. If you want to turn a screw, I'll take the screw driver.

First, here is a little history on how we got here. As telecommunications and storage costs dropped due to advancements in those technologies, it became more feasible to store larger amounts of data than ever before. This led to marketers investing heavily in targeted, one-to-one marketing in order to better understand and influence potential consumers of goods and services. As the databases grew larger, the queries started taking longer and longer. Eventually, engineers started looking for better solutions because relational databases (RDBMS) where not able to keep up with the demand.


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Written by Jerry Mattsson
This document was written some time ago but have not been published anywhere, so if anyone can use it, that is fine. I revised it and put some new comments in here and there. The contents is not version specific to the database but covers only PL/SQL version 2.
The purpose of this document is to serve as a practical guide or as a standard for programmers and system designers, writing, generating or specifying program modules that access an Oracle Rdbms. The conventions stated here should be applied as far as possible regardless of which tool or environment that are used to create or execute PL/SQL code.
This document may be included in your system design guidelines or standards, as long as it is included as is, or the reference is clearly stated.
Your own addition could be placed in an addendum or a preface, stating which parts that are used, changes to the parts used, or the parts that you want to exclude from your design guide.

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PHP Searching and Sorting Algorithm [17 exercises with solution]

[An editor is available at the bottom of the page to write and execute the scripts.]

1. Write a PHP program to sort a list of elements using Quick sort.Go to the editor
Quick sort is a comparison sort, meaning that it can sort items of any type for which a "less-than" relation (formally, a total order) is defined.
Click me to see the solution

2. Write a PHP program to sort a list of elements using Heap sort. Go to the editor
In computer science, heapsort (invented by J. W. J. Williams in 1964) is a comparison-based sorting algorithm. Heapsort can be thought of as an improved selection sort: like that algorithm, it divides its input into a sorted and an unsorted region, and it interactively shrinks the unsorted region by extracting the largest element and moving that to the sorted region. The improvement consists of the use of a heap data structure rather than a linear-time search to...

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