 # What types of algorithms are difficult to express MapReduce?

What types of algorithms are difficult to express MapReduce? A.
Algorithms that requite global, shared state.

B.
Large-scale graph algorithms that require one-step link traversal.

C.
Relational operations on large amounts of structured and semi structured data.

D.
Text analysis algorithms on large collections of unstructured text (e.g., Web crawls).

E.
Algorithms that require applying the same mathematical function to large numbers of individual
binary records.

Explanation:
See 3) below.
Limitations of Mapreduce–where not to use Mapreduce
While very powerful and applicable to a wide variety of problems, MapReduce is not the answer to
every problem. Here are some problems I found where MapReudce is not suited and some papers
that address the limitations of MapReuce.
1. Computation depends on previously computed values
If the computation of a value depends on previously computed values, then MapReduce cannot be
used. One good example is the Fibonacci series where each value is summation of the previous
two values. i.e., f(k+2) = f(k+1) + f(k). Also, if the data set is small enough to be computed on a
single machine, then it is better to do it as a single reduce(map(data)) operation rather than going
through the entire map reduce process.
2. Full-text indexing or ad hoc searching
The index generated in the Map step is one dimensional, and the Reduce step must not generate
a large amount of data or there will be a serious performance degradation. For example,
CouchDB’s MapReduce may not be a good fit for full-text indexing or ad hoc searching. This is a
problem better suited for a tool such as Lucene.
3. Algorithms depend on shared global state
Solutions to many interesting problems in text processing do not require global synchronization.As
a result, they can be expressed naturally in MapReduce, since map and reduce tasks run
independently and in isolation. However, there are many examples of algorithms that depend
crucially on the existence of shared global state during processing, making them difficult to
implement in MapReduce (since the single opportunity for global synchronization in MapReduce is
the barrier between the map and reduce phases of processing)
Reference: Limitations of Mapreduce–where not to use Mapreduce

## 2 Comments on “What types of algorithms are difficult to express MapReduce?”

1. Ramesh Hiremath says:

A.
Algorithms that requite global, shared state.

0

0
2. seenagape says: