What is overhead

Question

I am a student in Computer Science and I am hearing the word  overhead  a lot when it comes to programs and sorts  What does this mean exactly

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The meaning of the word can differ a lot with context  In general  it s resources  most often memory and CPU time  that are used  which do not contribute directly to the intended result  but are required by the technology or method that is being used  Examples    Protocol overhead  Ethernet frames  IP packets and TCP segments all have headers  TCP connections require handshake packets  Thus  you cannot use the entire bandwidth the hardware is capable of for your actual data  You can reduce the overhead by using larger packet sizes and UDP has a smaller header and no handshake  Data structure memory overhead  A linked list requires at least one pointer for each element it contains  If the elements are the same size as a pointer  this means a 50  memory overhead  whereas an array can potentially have 0  overhead  Method call overhead  A well-designed program is broken down into lots of short methods  But each method call requires setting up a stack frame  copying parameters and a return address  This represents CPU overhead compared to a program that does everything in a single monolithic function  Of course  the added maintainability makes it very much worth it  but in some cases  excessive method calls can have a significant performance impact

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its anything other than the data itself  ie tcp flags  headers  crc  fcs etc

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Overhead typically reffers to the amount of extra resources  memory  processor  time  etc   that different programming algorithms take   For example  the overhead of inserting into a balanced Binary Tree could be much larger than the same insert into a simple Linked List  the insert will take longer  use more processing power to balance the Tree  which results in a longer percieved operation time by the user

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Wikipedia has us covered      In computer science  overhead is   generally considered any combination   of excess or indirect computation   time  memory  bandwidth  or other   resources that are required to attain   a particular goal  It is a special   case of engineering overhead

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Think about the overhead as the time required to manage the threads and coordinate among them  It is a burden if the thread does not have enough task to do  In such a case the overhead cost over come the saved time through using threading and the code takes more time than the sequential one

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You can check Wikipedia  But mainly when more actions or resources are used  Like if you are familiar with  NET there you can have value types and reference types  Reference types have memory overhead as they require more memory than value types

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You re tired and cant do any more work  You eat food  The energy spent looking for food  getting it and actually eating it consumes energy and is overhead   Overhead is something wasted in order to accomplish a task  The goal is to make overhead very very small    In computer science lets say you want to print a number  thats your task  But storing the number  the setting up the display to print it and calling routines to print it  then accessing the number from variable are all overhead

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For a programmer overhead refers to those system resources which are consumed by your code when it s running on a giving platform on a given set of input data   Usually the term is used in the context of comparing different implementations or possible implementations   For example we might say that a particular approach might incur considerable CPU overhead while another might incur more memory overhead and yet another might weighted to network overhead  and entail an external dependency  for example    Let s give a specific example   Compute the average  arithmetic mean  of a set of numbers   The obvious approach is to loop over the inputs  keeping a running total and a count   When the last number is encountered  signaled by  end of file  EOF  or some sentinel value  or some GUI buttom  whatever  then we simply divide the total by the number of inputs and we re done   This approach incurs almost no overhead in terms of CPU  memory or other resources    It s a trivial task    Another possible approach is to  slurp  the input into a list  iterate over the list to calculate the sum  then divide that by the number of valid items from the list   By comparison this approach might incur arbitrary amounts of memory overhead   In a particular bad implementation we might perform the sum operation using recursion but without tail-elimination   Now  in addition to the memory overhead for our list we re also introducing stack overhead  which is a different sort of memory and is often a more limited resource than other forms of memory    Yet another  arguably more absurd  approach would be to post all of the inputs to some SQL table in an RDBMS   Then simply calling the SQL SUM function on that column of that table   This shifts our local memory overhead to some other server  and incurs network overhead and external dependencies on our execution    Note that the remote server may or may not have any particular memory overhead associated with this task --- it might shove all the values immediately out to storage  for example    Hypothetically might consider an implementation over some sort of cluster  possibly to make the averaging of trillions of values feasible    In this case any necessary encoding and distribution of the values  mapping them out to the nodes  and the collection collation of the results  reduction  would count as overhead   We can also talk about the overhead incurred by factors beyond the programmer s own code   For example compilation of some code for 32 or 64 bit processors might entail greater overhead than one would see for an old 8-bit or 16-bit architecture   This might involve larger memory overhead  alignment issues  or CPU overhead  where the CPU is forced to adjust bit ordering or used non-aligned instructions  etc  or both   Note that the disk space taken up by your code and it s libraries  etc  is not usually referred to as  overhead  but rather is called  footprint    Also the base memory your program consumes  without regard to any data set that it s processing  is called its  footprint  as well

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You could use a dictionary  The definition is the same  But to save you time  Overhead is work required to do the productive work  For instance  an algorithm runs and does useful work  but requires memory to do its work  This memory allocation takes time  and is not directly related to the work being done  therefore is overhead

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A concrete example of overhead is the difference between a  local  procedure call and a  remote  procedure call   For example  with classic RPC  and many other remote frameworks  like EJB   a function or method call looks the same to a coder whether its a local  in memory call  or a distributed  network call   For example   service function param1  param2     Is that a normal method  or a remote method  From what you see here you can t tell   But you can imagine that the difference in execution times between the two calls are dramatic   So  while the core implementation will  cost the same   the  overhead  involved is quite different

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It s the resources required to set up an operation  It might seem unrelated  but necessary   It s like when you need to go somewhere  you might need a car  But  it would be a lot of overhead to get a car to drive down the street  so you might want to walk  However  the overhead would be worth it if you were going across the country   In computer science  sometimes we use cars to go down the street because we don t have a better way  or it s not worth our time to  learn how to walk

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Overhead is simply the more time consumption in program execution  Example   when we call a function and its control is passed where it is defined and then its body is executed  this means that we make our CPU to run through a long process  first passing the control to other place in memory and then executing there and then passing the control back to the former position    consequently it takes alot performance  time  hence Overhead  Our goals are to reduce this overhead by using the inline during function definition and calling time  which copies the content of the function at the function call hence we dont pass the control to some other location  but continue our program in a line  hence inline

[overhead] What is "overhead"?

Examples related to overhead