Monday, November 30, 2015

MongoDB Fundamentals

MongoDB is a document-oriented DBMS. It uses JSON-like objects comprising the data model, rather than RDBMS tables. Significantly, MongoDB supports neither joins nor transactions. However, it features secondary indexes, an expressive query language, atomic writes on a per-document level, and fully-consistent reads. Operationally, MongoDB features master-slave replication with automated failover and built-in horizontal scaling via automated range-based partitioning.
Instead of tables, a MongoDB database stores its data in collections, which are the rough equivalent of RDBMS tables. A collection holds one or more documents, which corresponds to a record or a row in a relational database table, and each document has one or more fields, which corresponds to a column in a relational database table.
MongoDB Storage
A storage engine is the part of a database that is responsible for managing how data is stored on disk. Many databases support multiple storage engines, where different engines perform better for specific workloads. For example, one storage engine might offer better performance for read-heavy workloads, and another might support a higher-throughput for write operations. MMAPv1 is the default storage engine in 3.0. With multiple storage engines, you can decide which storage engine is best for your application.
MMAPv1 Storage Engine
A memory-mapped file is a file with data that the operating system places in memory by way of the mmap() system call. mmap() thus maps the file to a region of virtual memory. Memory-mapped files are the critical piece of the MMAPv1 storage engine in MongoDB. By using memory mapped files, MongoDB can treat the contents of its data files as if they were in memory. This provides MongoDB with an extremely fast and simple method for accessing and manipulating data.
MongoDB uses memory mapped files for managing and interacting with all data. Memory mapping assigns files to a block of virtual memory with a direct byte-for-byte correlation. MongoDB memory maps data files to memory as it accesses documents. Unaccessed data is not mapped to memory. Once mapped, the relationship between file and memory allows MongoDB to interact with the data in the file as if it were memory.

Database Properties
Atomicity and Transactions
In MongoDB, a write operation is atomic on the level of a single document, even if the operation modifies multiple embedded documents within a single document. When a single write operation modifies multiple documents, the modification of each document is atomic, but the operation as a whole is not atomic and other operations may interleave. However, we can isolate a single write operation that affects multiple documents using the $isolated operator.
Get more information at Concurrency.
MongoDB is consistent by default: reads and writes are issued to the primary member of a replica set. Applications can optionally read from secondary replicas, where data is eventually consistent by default. Reads from secondaries can be useful in scenarios where it is acceptable for data to be slightly out of date, such as some reporting applications. Applications can also read from the closest copy of the data (as measured by ping distance) when latency is more important than consistency.
Get more information at Consistency.

SOA : Service-Oriented Architecture

What is Service-Oriented Architecture?
Service-Oriented Architecture (SOA) is an architectural style. Applications built using an SOA style deliver functionality as services that can be used or reused when building applications or integrating within the enterprise or trading partners. It is a method of design, deployment, and management of both applications and the software infrastructure where:
  • All software is organized into business services that are network accessible and executable.
  • Service interfaces are based on public standards for interoperability.
Key Characteristics of SOA
  • Uses open standards to integrate software assets as services
  • Standardizes interactions of services
  • Services become building blocks that form business flows
  • Services can be reused by other applications
  • Quality of service, security and performance are specified
  • Software infrastructure is responsible for managing
  • Services are catalogued and discoverable
  • Data are catalogued and discoverable
  • Protocols use only industry standards
What is an Enterprise Service Bus (ESB)?
  • An enterprise service bus is an infrastructure used for building compound applications
  • The enterprise service bus is the glue that holds the compound application together
  • The enterprise service bus is an emerging style for integrating enterprise applications in an implementation-independent fashion
  • An enterprise service bus can be thought of as an abstraction layer on top of an Enterprise Messaging System
Key Characteristics of an ESB
  • Streamlines development
  • Supports multiple binding strategies
  • Performs data transformation
  • Intelligent routing
  • Real time monitoring
  • Exception handling
  • Service security