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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
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<head>
<title>How to Relocate a File Data Structure</title>
</head>
<body>
<h1>How to Relocate a File Data Structure</h1>
<p>Since file data structures can be cached in memory by the H5AC
package it becomes problematic to move such a data structure in
the file. One cannot just copy a portion of the file from one
location to another because:
<ol>
<li>the file might not contain the latest information, and</li>
<li>the H5AC package might not realize that the object's
address has changed and attempt to write the object to disk
at the old address.</li>
</ol>
<p>Here's a correct method to move data from one location to
another. The example code assumes that one is moving a B-link
tree node from <code>old_addr</code> to <code>new_addr</code>.
<ol>
<li>Make sure the disk is up-to-date with respect to the
cache. There is no need to remove the item from the cache,
hence the final argument to <code>H5AC_flush</code> is
<code>FALSE</code>.
<br><br>
<code>
H5AC_flush (f, H5AC_BT, old_addr, FALSE);<br>
</code>
<br>
</li>
<li>Read the data from the old address and write it to the new
address.
<br><br>
<code>
H5F_block_read (f, old_addr, size, buf);<br>
H5F_block_write (f, new_addr, size, buf);<br>
</code>
<br>
</li>
<li>Notify the cache that the address of the object changed.
<br><br>
<code>
H5AC_rename (f, H5AC_BT, old_addr, new_addr);<br>
</code>
<br>
</li>
</ol>
<hr>
<address><a href="mailto:robb@maya.nuance.com">Robb Matzke</a></address>
<!-- Created: Mon Jul 14 15:09:06 EST 1997 -->
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Last modified: Mon Jul 14 15:38:29 EST
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