summaryrefslogtreecommitdiffstats
path: root/doc/html/move.html
blob: b87e5406a397a898b2acb4727318b97be50eeff5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
<html>
  <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>Robb Matzke</address>
<!-- Created: Mon Jul 14 15:09:06 EST 1997 -->
<!-- hhmts start -->
Last modified: Mon Jul 14 15:38:29 EST 
<!-- hhmts end -->
  </body>
</html>