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From "Jiaqi Tan" <jiaqi....@gmail.com>
Subject HoD and locality of TaskTrackers to data (on DataNodes)
Date Sun, 23 Mar 2008 10:25:35 GMT

I have a question about using HoD and the locality of the assigned
TaskTrackers to the data.

Suppose I have a long-running HDFS installation with
TaskTrackers/JobTracker nodes dynamically allocated by HoD, and I
uploaded my data to HDFS prior to running my job/allocating nodes
using "dfs -put". Then, I allocate some nodes and run my job on that
data using HoD. Would the nodes allocated by HoD take into account the
HDFS nodes on which my data resides (e.g. by looking at which
DataNodes hold blocks that belong to the current user)? If the nodes
are just arbitrarily allocated, doesn't that break Hadoop's design
principle of having processing take place near the data?

And if HoD doesn't currently take block location into account when
allocating nodes, are there future plans for that to be incorporated?

Jiaqi Tan

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