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Hadoop Slides.lyx
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\begin_layout Title
Intro to Hadoop
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\begin_layout Author
Darrell Aucoin
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Stats Club
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In pioneer days they used oxen for heavy pulling, and when one ox couldn’t
budge a log, they didn’t try to grow a larger ox.
We shouldn’t be trying for bigger computers, but for more systems of computers.
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—Grace Hoppe
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Motivation
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Hadoop VS SQL
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RDBMS (SQL)
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Hadoop
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Data Size
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Gigabytes
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Terabyte/Petrabytes
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Access
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Interactive and batch
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Batch
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Updates
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Read and write many times
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Write once, read many times
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Structure
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Static schema (highly structured)
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Integrity
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High
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Low
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Scaling
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Nonlinear
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Data formating
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Normalized
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What is Hadoop?
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What is Hadoop?
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Hadoop MapReduce Components
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Controls job execution
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JobTracker Coordinates jobs, scheduling task for tasktrackers and records
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HDFS Components
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Hadoop MapReduce Components
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NameNode Manages the filesystem namespace: filesystem tree, metadata for
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Too many files on HDFS can slow the NameNode down
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Best to have input files at least a gigabyte in size
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DataNode Store and retrieve blocks
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Secondary
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Otherwise, copy metadata to secondary and run that as the new primary
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HDFS Federation
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\begin_deeper
\begin_layout Standard
To mange a large number of files, NameNodes require more and more memory:
\end_layout
\begin_layout Itemize
Hadoop 2.x addresses this by allowing mutliple NameNodes which each manages
a namespace volumne
\end_layout
\begin_deeper
\begin_layout Itemize
Metadata for namespace
\end_layout
\begin_layout Itemize
a block pool containing all the blocks for the file in the namespace
\end_layout
\end_deeper
\begin_layout Itemize
Each NameNode is independent of the other NameNodes and do not communicate
with each other
\end_layout
\end_deeper
\begin_layout Separator
\end_layout
\begin_layout Subsection
Hadoop Version 1.x vs 2.x
\end_layout
\begin_layout Frame
\begin_inset Argument 4
status open
\begin_layout Plain Layout
Hadoop Ver 1.x vs 2.x
\end_layout
\end_inset
\end_layout
\begin_deeper
\begin_layout Standard
s
\end_layout
\end_deeper
\begin_layout Separator
\end_layout
\begin_layout Subsection
MapReduce Phases
\end_layout
\begin_layout Frame
\begin_inset Argument 4
status open
\begin_layout Plain Layout
MapReduce Phases
\end_layout
\end_inset
\end_layout
\begin_deeper
\begin_layout Standard
s
\end_layout
\end_deeper
\begin_layout Separator
\end_layout
\begin_layout Frame
\begin_inset Argument 4
status open
\begin_layout Plain Layout
MapReduce Phases: Record Reader
\end_layout
\end_inset
\end_layout
\begin_deeper
\begin_layout Description
Record
\begin_inset space ~
\end_inset
Reader splits input into fixed-size pieces for each mapper with
\begin_inset Formula $k$
\end_inset
=positional information,
\begin_inset Formula $v=$
\end_inset
data
\end_layout
\begin_layout Standard
\begin_inset Formula
\[
\xymatrix{\\
& \mbox{Mapper 0} & & \mbox{Reducer 0}\\
\mbox{HDFS}\ar[ur]|-{\left(k_{1},v_{1}\right)}\ar[r]|-{\left(k_{1},v_{1}\right)}\ar[ddr]|-{\left(k_{1},v_{1}\right)} & \mbox{Mapper 1} & & \mbox{Reducer 1} & \mbox{HDFS}\\
& \vdots & & \vdots\\
& \mbox{Mapper M-1} & & \mbox{Reducer R-1}
}
\]
\end_inset
\end_layout
\end_deeper
\begin_layout Separator
\end_layout
\begin_layout Frame
\begin_inset Argument 4
status open
\begin_layout Plain Layout
MapReduce Phases: Map
\end_layout
\end_inset
\end_layout
\begin_deeper
\begin_layout Description
Map User defined function outputing intermediate key-value pairs for reducer
\end_layout
\begin_layout Standard
\begin_inset Formula
\[
\xymatrix{\\
& \mbox{Mapper 0}\ar@(ul,ur)^{{map}} & & \mbox{Reducer 0}\\
\mbox{HDFS}\ar[ur]|-{\left(k_{1},v_{1}\right)}\ar[r]|-{\left(k_{1},v_{1}\right)}\ar[ddr]|-{\left(k_{1},v_{1}\right)} & \mbox{Mapper 1}\ar@(ul,ur)^{{map}} & & \mbox{Reducer 1} & \mbox{HDFS}\\
& \vdots & & \vdots\\
& \mbox{Mapper M-1}\ar@(ul,ur)^{{map}} & & \mbox{Reducer R-1}
}
\]
\end_inset
\end_layout
\end_deeper
\begin_layout Separator
\end_layout
\begin_layout Frame
\begin_inset Argument 4
status open
\begin_layout Plain Layout
MapReduce Phases: Combiner (Optional)
\end_layout
\end_inset
\end_layout
\begin_deeper
\begin_layout Description
Combiner User defined function: aggregates data according to intermediate
keys on mapper node
\end_layout
\begin_layout Standard
\begin_inset Formula
\[
\xymatrix{\\
& \mbox{Mapper 0}\ar@(ul,ur)^{{map,combiner}} & & \mbox{Reducer 0}\\
\mbox{HDFS}\ar[ur]|-{\left(k_{1},v_{1}\right)}\ar[r]|-{\left(k_{1},v_{1}\right)}\ar[ddr]|-{\left(k_{1},v_{1}\right)} & \mbox{Mapper 1}\ar@(ul,ur)^{{map,combiner}} & & \mbox{Reducer 1} & \mbox{HDFS}\\
& \vdots & & \vdots\\
& \mbox{Mapper M-1}\ar@(ul,ur)^{{map,combiner}} & & \mbox{Reducer R-1}
}
\]
\end_inset
\end_layout
\end_deeper
\begin_layout Separator
\end_layout
\begin_layout Frame
\begin_inset Argument 4
status open
\begin_layout Plain Layout
MapReduce Phases: Partitioner
\end_layout
\end_inset
\end_layout
\begin_deeper
\begin_layout Description
Partitioner Sends intermediate key-value pairs
\begin_inset Formula $\left(k,v\right)$
\end_inset