100 lines
5.9 KiB
HTML
100 lines
5.9 KiB
HTML
|
<?xml version="1.0" encoding="UTF-8"?>
|
||
|
|
<!DOCTYPE html
|
||
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
||
|
|
<html lang="en-us" xml:lang="en-us">
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
||
|
|
<meta name="security" content="public" />
|
||
|
|
<meta name="Robots" content="index,follow" />
|
||
|
|
<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
|
||
|
|
<meta name="DC.Type" content="reference" />
|
||
|
|
<meta name="DC.Title" content="CPI4338 - &1 Access path(s) used for bitmap processing of file &2" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="pimes.htm" />
|
||
|
|
<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
|
||
|
|
<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
|
||
|
|
<meta name="DC.Format" content="XHTML" />
|
||
|
|
<meta name="DC.Identifier" content="cpi4338" />
|
||
|
|
<meta name="DC.Language" content="en-us" />
|
||
|
|
<!-- All rights reserved. Licensed Materials Property of IBM -->
|
||
|
|
<!-- US Government Users Restricted Rights -->
|
||
|
|
<!-- Use, duplication or disclosure restricted by -->
|
||
|
|
<!-- GSA ADP Schedule Contract with IBM Corp. -->
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ic.css" />
|
||
|
|
<title>CPI4338 - &1 Access path(s) used for bitmap processing of file &2</title>
|
||
|
|
</head>
|
||
|
|
<body id="cpi4338"><a name="cpi4338"><!-- --></a>
|
||
|
|
<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
|
||
|
|
<h1 class="topictitle1">CPI4338 - &1 Access path(s) used for bitmap processing of file &2</h1>
|
||
|
|
<div>
|
||
|
|
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><thead align="left"><tr><th colspan="2" align="center" valign="middle" id="d0e16">CPI4338</th>
|
||
|
|
</tr>
|
||
|
|
</thead>
|
||
|
|
<tbody><tr valign="middle"><td valign="middle" width="26.02040816326531%" headers="d0e16 ">Message Text:</td>
|
||
|
|
<td valign="middle" width="73.9795918367347%" headers="d0e16 ">&1 Access path(s) used for bitmap processing of file &2.</td>
|
||
|
|
</tr>
|
||
|
|
<tr valign="middle"><td valign="middle" width="26.02040816326531%" headers="d0e16 ">Cause Text:</td>
|
||
|
|
<td valign="middle" width="73.9795918367347%" headers="d0e16 ">Bitmap processing was used to access records from member &4 of
|
||
|
|
file &2 in library &3. <p></p>
|
||
|
|
Bitmap processing is a method
|
||
|
|
of allowing one or more access path(s) to be used to access the selected records
|
||
|
|
from a file. Using bitmap processing, record selection is applied against
|
||
|
|
each access path, similar to key row positioning, to create a bitmap. The
|
||
|
|
bitmap has marked in it only the records of the file that are to be selected.
|
||
|
|
If more than one access path is used, the resulting bitmaps are merged together
|
||
|
|
using boolean logic. The resulting bitmap is then used to reduce access to
|
||
|
|
just those records actually selected from the file. <p></p>
|
||
|
|
Bitmap
|
||
|
|
processing is used in conjunction with the two primary access methods: arrival
|
||
|
|
sequence (CPI4327 or CPI4329) or keyed access (CPI4326 or CPI4328). The message
|
||
|
|
that describes the primary access method immediately precedes this message.
|
||
|
|
<p></p>
|
||
|
|
When the bitmap is used with the keyed access method then it
|
||
|
|
is used to further reduce the number of records selected by the primary access
|
||
|
|
path before retrieving the selected records from the file. <p></p>
|
||
|
|
When
|
||
|
|
the bitmap is used with arrival sequence then it allows the sequential scan
|
||
|
|
of the file to skip records which are not selected by the bitmap. This is
|
||
|
|
called skip sequential processing. <p></p>
|
||
|
|
The list below shows the
|
||
|
|
names of the access paths used in the bitmap processing: <p></p>
|
||
|
|
If
|
||
|
|
file &2 in library &3 is a logical file then member &7 of physical
|
||
|
|
file &5 in library &6 is the actual file being accessed.</td>
|
||
|
|
</tr>
|
||
|
|
<tr valign="middle"><td valign="middle" width="26.02040816326531%" headers="d0e16 ">Recovery Text:</td>
|
||
|
|
<td valign="middle" width="73.9795918367347%" headers="d0e16 ">Refer to <a href="rzajqdta.htm#rzajqdta">Data access on DB2 UDB for iSeries: data access paths and methods</a> for more information
|
||
|
|
about bitmap processing.</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>The optimizer chooses to use one or more indexes, in conjunction
|
||
|
|
with the query selection (WHERE clause), to build a bitmap. This resulting
|
||
|
|
bitmap indicates which rows will actually be selected.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>Conceptually, the bitmap contains one bit per row in the underlying
|
||
|
|
table. Corresponding bits for selected rows are set to '1'. All other bits
|
||
|
|
are set to '0'.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>Once the bitmap is built, it is used, as appropriate, to avoid
|
||
|
|
mapping in rows from the table not selected by the query. The use of the bitmap
|
||
|
|
depends on whether the bitmap is used in combination with the arrival sequence
|
||
|
|
or with a primary index.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>When bitmap processing is used with arrival sequence, either message
|
||
|
|
CPI4327 or CPI4329 will precede this message. In this case, the bitmap will
|
||
|
|
help to selectively map only those rows from the table that the query selected.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>When bitmap processing is used with a primary index, either message
|
||
|
|
CPI4326 or CPI4328 will precede this message. Rows selected by the primary
|
||
|
|
index will be checked against the bitmap before mapping the row from the table.</p>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div>
|
||
|
|
<div class="familylinks">
|
||
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="pimes.htm" title="You can evaluate the structure and performance of the given SQL statements in a program using informational messages put in the job log by the database manager.">Query optimization performance information messages</a></div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
</html>
|