Database Reference
In-Depth Information
5
However, we show in
Section 2.6.7
that two passes of MapReduce are usually better than one for matrix multiplica-
tion.
6
This algorithm uses much too much communication, but it will serve as a simple example of the Pregel computation
model.
7
Recall that this figure represented functions, not tasks. As a network of tasks, there would be, for example, many tasks
implementing function
f
, each of which feeds data to each of the tasks for function
g
and each of the tasks for function
i
.
8
This person, or more generally, people with large extended circles of friends, are good people to use to start a market-
ing campaign by giving them free samples.
9
In a typical cluster, there are many switches connecting subsets of the compute nodes, so all the data does not need to
go across a single gigabit switch. However, the total available communication is still small enough that it is not feas-
ible to implement this algorithm for the scale of data we have hypothesized.
10
If
q
is less than 2
n
, then a reducer cannot get even one row and one column, and therefore cannot compute any out-
puts at all.
11
Bit strings have
Hamming distance 1
if they differ in exactly one bit position. You may look ahead to
Section 3.5.6
for the general definition.
