[svn-r779] Changes since 19981022

---------------------- ./MANIFEST ./doc/html/study.html [DELETED] ./doc/html/study_1000x1000.gif [DELETED] ./doc/html/study_250x250.gif [DELETED] ./doc/html/study_499x499.gif [DELETED] ./doc/html/study_5000x1000.gif [DELETED] ./doc/html/study_500x500.gif [DELETED] ./doc/html/study_p1.gif [DELETED] ./doc/html/study_p1.obj [DELETED] Removed these old files -- the data was from before the chunk cache was implemented and therefore the whole file was pretty much garbage. ./MANIFEST ./doc/html/Chunking.html [NEW] ./doc/html/Chunk_f1.gif [NEW] ./doc/html/Chunk_f1.obj [NEW] ./doc/html/Chunk_f2.gif [NEW] ./doc/html/Chunk_f2.obj [NEW] ./doc/html/Chunk_f3.gif [NEW] ./doc/html/Chunk_f4.gif [NEW] ./doc/html/Chunk_f5.gif [NEW] ./doc/html/Chunk_f6.gif [NEW] ./doc/html/Chunk_f6.obj [NEW] New documentation for chunking. It's not quite complete but it gives a pretty good idea of some of the issues affecting performance.
author: Robb Matzke <matzke@llnl.gov> 1998-10-23 15:44:02 (GMT)
committer: Robb Matzke <matzke@llnl.gov> 1998-10-23 15:44:02 (GMT)
commit: e1d1bf607f2128d0066b6f4a50c61d91e8732db7 (patch)
tree: 65d8b24696174defb222a41c9b52288ba4aa6248 /doc
parent: 97621ca893aeebe459bb91265525b6409dc0a5b9 (diff)
download: hdf5-e1d1bf607f2128d0066b6f4a50c61d91e8732db7.zip
hdf5-e1d1bf607f2128d0066b6f4a50c61d91e8732db7.tar.gz
hdf5-e1d1bf607f2128d0066b6f4a50c61d91e8732db7.tar.bz2
8 files changed, 0 insertions, 285 deletions
diff --git a/doc/html/study.html b/doc/html/study.html
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-<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
-<html>
-  <head>
-    <title>Testing the chunked layout of HDF5</title>
-  </head>
-
-  <body>
-    <h1>Testing the chunked layout of HDF5</h1>
-
-    <p>This is the results of studying the chunked layout policy in
-      HDF5. A 1000 by 1000 array of integers was written to a file
-      dataset extending the dataset with each write to create, in the
-      end, a 5000 by 5000 array of 4-byte integers for a total data
-      storage size of 100 million bytes.
-
-    <p>
-      <center>
-	<img alt="Order that data was written" src="study_p1.gif">
-	<br><b>Fig 1: Write-order of Output Blocks</b>
-      </center>
-
-    <p>After the array was written, it was read back in blocks that
-      were 500 by 500 bytes in row major order (that is, the top-left
-      quadrant of output block one, then the top-right quadrant of
-      output block one, then the top-left quadrant of output block 2,
-      etc.).
-
-    <p>I tried to answer two questions:
-    <ul>
-      <li>How does the storage overhead change as the chunk size
-	changes?
-      <li>What does the disk seek pattern look like as the chunk size
-	changes?
-    </ul>
-
-    <p>I started with chunk sizes that were multiples of the read
-      block size or k*(500, 500).
-
-    <p>
-      <center>
-	<table border>
-	  <caption align=bottom>
-	    <b>Table 1: Total File Overhead</b>
-	  </caption>
-	  <tr>
-	    <th>Chunk Size (elements)</th>
-	    <th>Meta Data Overhead (ppm)</th>
-	    <th>Raw Data Overhead (ppm)</th>
-	  </tr>
-
-	  <tr align=center>
-	    <td>500 by 500</td>
-	    <td>85.84</td>
-	    <td>0.00</td>
-	  </tr>
-	  <tr align=center>
-	    <td>1000 by 1000</td>
-	    <td>23.08</td>
-	    <td>0.00</td>
-	  </tr>
-	  <tr align=center>
-	    <td>5000 by 1000</td>
-	    <td>23.08</td>
-	    <td>0.00</td>
-	  </tr>
-	  <tr align=center>
-	    <td>250 by 250</td>
-	    <td>253.30</td>
-	    <td>0.00</td>
-	  </tr>
-	  <tr align=center>
-	    <td>499 by 499</td>
-	    <td>85.84</td>
-	    <td>205164.84</td>
-	  </tr>
-	</table>
-      </center>
-
-    <hr>
-    <p>
-      <center>
-	<img alt="500x500" src="study_500x500.gif">
-	<br><b>Fig 2: Chunk size is 500x500</b>
-      </center>
-
-    <p>The first half of Figure 2 shows output to the file while the
-      second half shows input.  Each dot represents a file-level I/O
-      request and the lines that connect the dots are for visual
-      clarity. The size of the request is not indicated in the
-      graph. The output block size is four times the chunk size which
-      results in four file-level write requests per block for a total
-      of 100 requests. Since file space for the chunks was allocated
-      in output order, and the input block size is 1/4 the output
-      block size, the input shows a staircase effect.  Each input
-      request results in one file-level read request. The downward
-      spike at about the 60-millionth byte is probably the result of a
-      cache miss for the B-tree and the downward spike at the end is
-      probably a cache flush or file boot block update.
-
-    <hr>
-    <p>
-      <center>
-	<img alt="1000x1000" src="study_1000x1000.gif">
-	<br><b>Fig 2: Chunk size is 1000x1000</b>
-      </center>
-
-    <p>In this test I increased the chunk size to match the output
-      chunk size and one can see from the first half of the graph that
-      25 file-level write requests were issued, one for each output
-      block.  The read half of the test shows that four times the
-      amount of data was read as written.  This results from the fact
-      that HDF5 must read the entire chunk for any request that falls
-      within that chunk, which is done because (1) if the data is
-      compressed the entire chunk must be decompressed, and (2) the
-      library assumes that a chunk size was chosen to optimize disk
-      performance.
-
-    <hr>
-    <p>
-      <center>
-	<img alt="5000x1000" src="study_5000x1000.gif">
-	<br><b>Fig 3: Chunk size is 5000x1000</b>
-      </center>
-
-    <p>Increasing the chunk size further results in even worse
-      performance since both the read and write halves of the test are
-      re-reading and re-writing vast amounts of data.  This proves
-      that one should be careful that chunk sizes are not much larger
-      than the typical partial I/O request.
-
-    <hr>
-    <p>
-      <center>
-	<img alt="250x250" src="study_250x250.gif">
-	<br><b>Fig 4: Chunk size is 250x250</b>
-      </center>
-
-    <p>If the chunk size is decreased then the amount of data
-      transfered between the disk and library is optimal for no
-      caching, but the amount of meta data required to describe the
-      chunk locations increases to 250 parts per million.  One can
-      also see that the final downward spike contains more file-level
-      write requests as the meta data is flushed to disk just before
-      the file is closed.
-
-    <hr>
-    <p>
-      <center>
-	<img alt="499x499" src="study_499x499.gif">
-	<br><b>Fig 4: Chunk size is 499x499</b>
-      </center>
-
-    <p>This test shows the result of choosing a chunk size which is 
-      close to the I/O block size.  Because the total size of the
-      array isn't a multiple of the chunk size, the library allocates
-      an extra zone of chunks around the top and right edges of the
-      array which are only partially filled.  This results in
-      20,516,484 extra bytes of storage, a 20% increase in the total
-      raw data storage size.  But the amount of meta data overhead is
-      the same as for the 500 by 500 test.  In addition, the mismatch
-      causes entire chunks to be read in order to update a few
-      elements along the edge or the chunk which results in a 3.6-fold
-      increase in the amount of data transfered.
-
-    <hr>
-    <address><a href="mailto:matzke@llnl.gov">Robb Matzke</a></address>
-<!-- Created: Fri Jan 30 21:04:49 EST 1998 -->
-<!-- hhmts start -->
-Last modified: Fri Jan 30 23:51:31 EST 1998
-<!-- hhmts end -->
-  </body>
-</html>
diff --git a/doc/html/study_1000x1000.gif b/doc/html/study_1000x1000.gif
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author	Robb Matzke <matzke@llnl.gov>	1998-10-23 15:44:02 (GMT)
committer	Robb Matzke <matzke@llnl.gov>	1998-10-23 15:44:02 (GMT)
commit	e1d1bf607f2128d0066b6f4a50c61d91e8732db7 (patch)
tree	65d8b24696174defb222a41c9b52288ba4aa6248 /doc
parent	97621ca893aeebe459bb91265525b6409dc0a5b9 (diff)
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