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What is meant by Operation is costly or the resource is costly in-terms of Software. When i come across with some documents they mentioned something like Opening a file every-time is a Costly Operation. I can have more examples like this (Database connection is a costly operation, Thread pool is a cheaper one, etc..). At what basis it decided whether the task or operation is costly or cheaper? When we calculating this what the constraints to consider? Is based on the Time also?

Note : I already checked in the net with this but i didn't get any good explanation. If you found kindly share with me and i can close this..

AstroCB
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Miko
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Expensive or Costly operations are those which cause a lot of resources to be used, such as the CPU, Disk Drive(s) or Memory

For example, creating an integer variable in code is not a costly or expensive operation

By contrast, creating a connection to a remote server that hosts a relational database, querying several tables and returning a large results set before iterating over it while remaining connected to the data source would be (relatively) expensive or costly, as opposed to my first example with the Integer.

In order to build scalable, fast applications you would generally want to minimize the frequency of performing these costly/expensive actions, applying techniques of optimisation, caching, parallelism (etc) where they are essential to the operation of the software.

To get a degree of accuracy and some actual numbers on what is 'expensive' and what is 'cheap' in your application, you would employ some sort of profiling or analysis tool. For JavaScript, there is ySlow - for .NET applications, dotTrace - I'd be certain that whatever the platform, a similar solution exists. It's then down to someone to comprehend the output, which is probably the most important part!

SpaceBison
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Running time, memory use or bandwidth consumption are the most typical interpretations of "cost". Also consider that it may apply to cost in development time.

Wouter Lievens
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I'll try explain through some examples:

If you need to edit two field in each row of a Database, if you do it one field at a time that's gonna be close to twice the time as if it was properly done both at same time.

This extra time was not only your waste of time, but also a connection opened longer then needed, memory occupied longer then needed and at the end of the day, your eficience goes down the drain.

When you start scalling, very small amount of time wasted grows into a very big waste of Company resources.

Pedro Ferreira
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It is almost certainly talking about a time penalty to perform that kind of input / output. Lots of memory shuffling (copying of objects created from classes with lots of members) is another time waster (pass by reference helps eliminate a lot of this).

JTeagle
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Usually costly means, in a very simplified way, that it'll take much longer then an operation on memory.

For instance, accessing a File in your file system and reading each line takes much longer then simply iterating over a list of the same size in memory. The same can be said about database operations, they take much longer then in-memory operations, and so some caution should be used not to abuse these operations.

This is, I repeat, a very simplistic explanation. Exactly what costly means depends on your particular context, the number of operations you're performing, and the overall architecture of the system.

pcalcao
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