Nrthugu

What is the difference between coarse-grained and fine-grained?

I have searched these terms on Google, but I couldn't find what they mean.

From Wikipedia (granularity):

Granularity is the extent to which a
system is broken down into small
parts, either the system itself or its
description or observation. It is the
extent to which a larger entity is
subdivided. For example, a yard broken
into inches has finer granularity than
a yard broken into feet.

Coarse-grained systems consist of
fewer, larger components than
fine-grained systems; a coarse-grained
description of a system regards large
subcomponents while a fine-grained
description regards smaller components
of which the larger ones are composed.

In simple terms

• 
  Coarse-grained - larger components than fine-grained, large subcomponents. Simply wraps one or more fine-grained services together into a more coarse­-grained operation.


• 
  Fine-grained - smaller components of which the larger ones are composed, lower­level service

It is better to have more coarse-grained service operations, which are composed by fine-grained operations

Coarse-grained: A few ojects hold a lot of related data that's why services have broader scope in functionality. Example: A single "Account" object holds the customer name, address, account balance, opening date, last change date, etc.
Thus: Increased design complexity, smaller number of cells to various operations

Fine-grained: More objects each holding less data that's why services have more narrow scope in functionality. Example: An Account object holds balance, a Customer object holds name and address, a AccountOpenings object holds opening date, etc.
Thus: Decreased design complexity , higher number of cells to various service operations.
These are relationships defined between these objects.

One more way to understand would be to think in terms of communication between processes and threads. Processes communicate with the help of coarse grained communication mechanisms like sockets, signal handlers, shared memory, semaphores and files. Threads, on the other hand, have access to shared memory space that belongs to a process, which allows them to apply finer grain communication mechanisms.

Source: Java concurrency in practice

In the context of services:

http://en.wikipedia.org/wiki/Service_Granularity_Principle

By definition a coarse-grained service operation has broader scope
than a fine-grained service, although the terms are relative. The
former typically requires increased design complexity but can reduce
the number of calls required to complete a task.

A fine grained service interface is about the same like chatty interface.

Coarse-grained granularity does not always mean bigger components, if you go by literally meaning of the word coarse, it means harsh, or not appropriate. e.g. In software projects management, if you breakdown a small system into few components, which are equal in size, but varies in complexities and features, this could lead to a coarse-grained granularity. In reverse, for a fine-grained breakdown, you would divide the components based on their cohesiveness of the functionalities each component is providing.

coarse grained and fine grained. Both of these modes define how the cores are shared
between multiple Spark tasks. As the name suggests, fine-grained mode is
responsible for sharing the cores at a more granular level. Fine-grained mode has been deprecated by Spark and will soon be removed.

In term of dataset like a text file ,Coarse-grained meaning we can transform the whole dataset but not an individual element on the dataset While fine-grained means we can transform individual element on the dataset.

Coarse-grained and Fine-grained both think about optimizing a number of servicess. But the difference is in the level. I like to explain with an example, you will understand easily.

Fine-grained: For example, I have 100 services like findbyId, findbyCategry, findbyName...... so on. Instead of that many services why we can not provide find(id, category, name....so on). So this way we can reduce the services. This is just an example, but the goal is how to optimize the number of services.

Coarse-grained: For example, I have 100 clients, each client have their own set of 100 services. So I have to provide 100*100 total services. It is very much difficult. Instead of that what I do is, I identify all common services which apply to most of the clients as one service set and remaining separately. For example in 100 services 50 services are common. So I have to manage 100*50 + 50 only.