CODEWITHSUNDEEP
memory
Lucky
Lucky

Reputation: 209

Mapping and allocating

I am little confused with term mapping, for example, when we say mapping memory for database, it means that we assigning specific amount of memory at some memory location to that database?

Also is allocating memory synonym for reserving memory?

Very often I encounter these two terms, and they aren't so clear to me.

If someone can clarify these two terms, I will be very thankful.

Upvotes: 3

Views: 913

Answers (2)

gbulmer
gbulmer

Reputation: 4290

This might be a question better asked to the software community at stackoverflow. However, I am a CS.

I would say that terms aren't always used accurately and precisely.

In general allocating memory is making memory available to a program for an active purpose, such as allocating memory for buffers to hold a file or in in-memory structure now.

Reserving memory is often used to mean the same thing. However, it is sometimes more passive. For example reserving memory in case their is a future requirement, or protecting against too much memory allocation for a different purpose.

Often when the term 'mapping' is used, it is for a file. It may mean exactly the same as allocating. Or it means more; mapping may be using an underlying mechanism provided by virtual memory management systems, where part of virtual memory is 'mapped' to the file, without actually reading the file into physical memory. The trick is, as the memory-mapped file is accessed, the block/page being accessed is read in 'invisibly' to the process when necessary. This uses a mechanism called demand paging. It's benefit is a program can access the file as if it is all read into memory, but only the parts actually accessed are retrieved from the persistent storage system (disk, flash, whatever), which can be a huge win if only small parts of the file are needed.

Further, it simplifies the program, which can be written as if the whole file is in memory. Instead of the application developer trying to keep track of which parts of the file have been loaded into memory, the operating system does that instead.

Even better, the Operating system can be asked to track which blocks/pages have their contents changed, and it can be asked to periodically write that back out to persistent storage. This can even further simplify the application program.

This is popular with some databases.

Upvotes: 1

Jssamp
Jssamp

Reputation:

Mapping basically means assigning. Except we often want a 1 to 1 mapping in the case of functions. If you define the function of an object, physical or just logical, and define it's relationships and how it changes under transformation then you have mapped it.

Upvotes: 0

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