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From: Sugandha Naolekar <sugandha.n87@gmail.com>
Date: Tue, 25 Feb 2014 11:27:08 +0530
Message-ID: 
 <CAGcQziEiLHQ4WiAQeiQByWCqqzxEx0M4G78e0tAw7AfgO+LR4g@mail.gmail.com>
Subject: Mappers vs. Map tasks
To: "core-user@hadoop.apache.org" <user@hadoop.apache.org>
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--089e0160bf7096dd4904f334c444
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Hello,

As per the various articles I went through till date, the File(s) are split
in chunks/blocks. On the same note, would like to ask few things:


   1. No. of mappers are decided as: Total_File_Size/Max. Block Size. Thus,
   if the file is smaller than the block size, only one mapper will be
   invoked. Right?
   2. If yes, it means, the map() will be called only once. Right? In this
   case, if there are two datanodes with a replication factor as 1: only one
   datanode(mapper machine) will perform the task. Right?
   3. The map() function is called by all the datanodes/slaves right? If
   the no. of mappers are more than the no. of slaves, what happens?

--
Thanks & Regards,
Sugandha Naolekar

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Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr"><div class=3D"gmail_default" style=3D"font-family:georgia,=
serif;color:rgb(255,0,0)">Hello,<br><br></div><div class=3D"gmail_default" =
style=3D"font-family:georgia,serif;color:rgb(255,0,0)">As per the various a=
rticles I went through till date, the File(s) are split in chunks/blocks. O=
n the same note, would like to ask few things:<br>

<br><ol><li>No. of mappers are decided as: Total_File_Size/Max. Block Size.=
 Thus, if the file is smaller than the block size, only one mapper will be =
invoked. Right?</li><li>If yes, it means, the map() will be called only onc=
e. Right? In this case, if there are two datanodes with a replication facto=
r as 1: only one datanode(mapper machine) will perform the task. Right?</li=
>

<li>The map() function is called by all the datanodes/slaves right? If the =
no. of mappers are more than the no. of slaves, what happens?<br></li></ol>=
</div><div><div dir=3D"ltr"><div><font color=3D"#674ea7" face=3D"georgia, s=
erif">--</font></div>

<div><font color=3D"#674ea7" face=3D"georgia, serif"><span style=3D"border-=
collapse:collapse;font-size:13px">Thanks &amp;=A0Regards,<br>Sugandha Naole=
kar<br></span><br></font><div><font color=3D"#674ea7" face=3D"georgia, seri=
f"><br>
</font><div>
<div style=3D"font-size:10px"><br></div></div></div></div></div></div>
</div>

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