Facebook Thrift
Thrift is a software library and a set of code generation tool
which was developed at the Facebook Office at Palo Alto, California, to
expedite development and implementation of scalable and efficient
backend services. The primary goal of thrift is enable efficient and
reliable communication across programming languages by abstracting the
portions of each language that tend to require the most customization
into a common library that is implemented in each language. This is done
by allowing the users to define the data types and service interfaces
in a common Interface Definition Logic File (IDL File) which is supposed
to be language neutral file and it generates all the necessary code to
build Remote Procedure Calls to clients and servers. This report
explains the design choices and implementation level details and also
tries to demonstrate a sample Thrift Service.
The whole concept of Thrift stemmed out from the fact that a new direction was required to tackle the resource demands problems for many of Facebook's on-site applications, which couldn’t be addressed by staying within the LAMP framework. LAMP is the acronym for Linux, MySQL, Apache and PHP. When Facebook was being laboriously designed, it was done from ground up using this LAMP framework. By 2006 Facebook was widely accepted all over the world as the social networking site and consequently its network traffic also grew giving rise to the need for scaling its network structure for many of its onsite applications like, search, ad selection and delivery and event logging.
Scaling these operations to match the resource demands was not possible within the LAMP framework. In their implementation of creating many of these services like search, event logging various programming languages had been selected to optimize for the right combination of performance, ease and speed of development, availability of existing libraries etc. Also a large portion of the Facebook's culture has always preferred to choose the best tools and implementations over the standardizing on any one programming language and begrudgingly accepting its inherent limitations. Most of the programming languages either suffered from subpar performance or constrained data type freedom. Given all these technical challenges and design choices, the engineers at Facebook were presented with a herculean task of building a scalable, transparent and high performance bridge across various programming languages.
The whole concept of Thrift stemmed out from the fact that a new direction was required to tackle the resource demands problems for many of Facebook's on-site applications, which couldn’t be addressed by staying within the LAMP framework. LAMP is the acronym for Linux, MySQL, Apache and PHP. When Facebook was being laboriously designed, it was done from ground up using this LAMP framework. By 2006 Facebook was widely accepted all over the world as the social networking site and consequently its network traffic also grew giving rise to the need for scaling its network structure for many of its onsite applications like, search, ad selection and delivery and event logging.
Scaling these operations to match the resource demands was not possible within the LAMP framework. In their implementation of creating many of these services like search, event logging various programming languages had been selected to optimize for the right combination of performance, ease and speed of development, availability of existing libraries etc. Also a large portion of the Facebook's culture has always preferred to choose the best tools and implementations over the standardizing on any one programming language and begrudgingly accepting its inherent limitations. Most of the programming languages either suffered from subpar performance or constrained data type freedom. Given all these technical challenges and design choices, the engineers at Facebook were presented with a herculean task of building a scalable, transparent and high performance bridge across various programming languages.
Thrift Design Features
The primary idea behind Thrift is that it consists of a language
neutral stack which is implemented across various programming languages
and an associated code generation engine which transforms a simple
interface and data definition language into client and server remote
procedure call libraries. Thrift is designed to be as simple as possible
for the developers who can define all the necessary data structures and
interfaces for a complex service in a single short file. This file is
called as Thrift Interface Definition Logic File or Thrift IDL File. The
developers identified some important features while evaluating the
technical challenges of cross language interactions in a networked
environment.
Thrift allows programmers to develop completely using thrift's native data type rather than using any wrapper objects or special dynamic types. It also does not require the developer to write any serialization code for transport. The developer is given the freedom to logically annotate their data structures in Thrift Interface Definition Logic File (IDL File), with minimal amount of extra information necessary to tell the code generator how to safely transport the objects across languages.
This is how a Thrift Struct looks like,
struct Example
{
1: i32 number =10,
2: i64 bignumber,
3: double decimals,
4: string name= “NB”
};
As you can see the fields inside the Thrift struct are labeled with unique field identifiers.
Thrift has enabled Facebook to build scalable backend services efficiently by enabling engineers to divide and conquer. Application developers can focus on application code without worrying about the sockets layer. We avoid duplicated work by writing buffering and I/O logic in one place, rather than interspersing it in each application. Thrift has been employed in a wide variety of applications at Facebook, including search, logging, mobile, ads, and the developer platform. We have found that the marginal performance cost incurred by an extra layer of software abstraction is far eclipsed by the gains in developer efficiency and systems reliability. Finally Thrift has been added to Apache Software Foundation as the Apache Thrift Project , making it open source framework for cross-language services implementation.
Types:
A common type system should exist across all the programming
languages without requiring the need for the developers to write their
own serialization code. Serialization is the process of transforming an
object of one type to another. For example if a programmer has written
an application implementing a strongly typed STL map for a Python
dictionary. Neither programmer should be forced to write any code below
the application layer. Dictionary is a data type in Python which allows
sequencing a collection of items or elements using keys. It is very
similar to 'Associative Arrays'.
Transport:
Each language must have a common interface to bidirectional raw
data transport. Consider a scenario where there are 2 servers in which,
one is deployed in Java and the other one is deployed in Python. So a
typical service written in Java should be able to send the raw data from
that service to a common interface which will be understood by the
other server which is running on Python and vice-versa. The Transport
Layer should be able to transport the raw data file across the two ends.
The specifics about how this transport is implemented shouldn’t matter
to the service developer. The same application code should be able to
run against TCP Stream Sockets, raw data in memory or files on disk.
Protocol:
In order to transport the raw data, they have to be encoded into a
particular format like binary, XML etc. Therefore the Transport Layer
uses some particular protocol to encode or decode the data. Again the
application developer will not be bothered about this. He is only
worried whether the data can be read or written in some deterministic
manner.
Versioning:
For the services to be robust they must evolve from their present
version. They should incorporate new features and in order to do this
the data types involved in the service should provide a mechanism to add
or delete fields of an object or alter the arguments list of a function
without any interruption in service. This is called Versioning.
Processors:
Processors are the ones which process the data streams and accomplish Remote Procedure Calls.Thrift allows programmers to develop completely using thrift's native data type rather than using any wrapper objects or special dynamic types. It also does not require the developer to write any serialization code for transport. The developer is given the freedom to logically annotate their data structures in Thrift Interface Definition Logic File (IDL File), with minimal amount of extra information necessary to tell the code generator how to safely transport the objects across languages.
Structs:
A thrift struct defines a common object to be used across languages. A struct is essentially similar to a class in object oriented programming languages. A Thrift struct has a strongly typed field with unique field identifiers. The basic syntax for Thrift struct is very similar to the structs used in C. The fields in a Thrift struct may be annotated with unique field identifiers unique to the scope of the struct and also with optional default values. The concept of field identifiers can be omitted also and this concept of field identifers was introduced strictly for versioning purposes.This is how a Thrift Struct looks like,
struct Example
{
1: i32 number =10,
2: i64 bignumber,
3: double decimals,
4: string name= “NB”
};
As you can see the fields inside the Thrift struct are labeled with unique field identifiers.
Facebook Thrift Services
Thrift has been employed in a large number of applications at
Facebook, including search, logging, mobile, ads and the developer
platform. Two specific usages are discussed below.
Search
Thrift is used as the underlying protocol and transport layer for
the Facebook Search service. The multi-language code generation is well
suited for search because it allows for application development in an
efficient server side language (C++) and allows the Facebook PHP-based
web application to make calls to the search service using Thrift PHP
libraries. There is also a large variety of search stats, deployment and
testing functionality that is built on top of generated Python code.
Additionally, the Thrift log file format is used as a redo log for
providing real-time search index updates. Thrift has allowed the search
team to leverage each language for its strengths and to develop code at a
rapid pace.
Logging
The Thrift TFileTransport functionality is used for structured
logging. Each service function definition along with its parameters can
be considered to be a structured log entry identified by the function
name. This log can then be used for a variety of purposes, including
online and offline processing, stats aggregation and as a redo log.Thrift has enabled Facebook to build scalable backend services efficiently by enabling engineers to divide and conquer. Application developers can focus on application code without worrying about the sockets layer. We avoid duplicated work by writing buffering and I/O logic in one place, rather than interspersing it in each application. Thrift has been employed in a wide variety of applications at Facebook, including search, logging, mobile, ads, and the developer platform. We have found that the marginal performance cost incurred by an extra layer of software abstraction is far eclipsed by the gains in developer efficiency and systems reliability. Finally Thrift has been added to Apache Software Foundation as the Apache Thrift Project , making it open source framework for cross-language services implementation.
References
Kempf, Williams, “Boost. Threads”, http://www.boost.org/doc/html.Thrift White Paper, http://thrift.apache.org/static/thrift- 20070401.pdf.
Thrift Tutorial http://wiki.apache.org/thrift/Tutorial.
Thrift Wiki http://wiki.apache.org/thrift.
Protocol Buffers
http://code.google.com/apis/protocolbuffers/docs/overview.html
