119 lines
8.0 KiB
HTML
119 lines
8.0 KiB
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="DC.Title" content="Example: Analyze the RW trace data" />
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<meta name="abstract" content="This discussion examines the elements that make up the data stream in the example." />
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<meta name="description" content="This discussion examines the elements that make up the data stream in the example." />
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<meta name="DC.subject" content="analyzing, RW trace data, trace data, example, analyzing the RW trace data" />
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<title>Example: Analyze the RW trace data </title>
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<body id="rbal1anrwtr"><a name="rbal1anrwtr"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Example: Analyze the RW trace data </h1>
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<div><p>This discussion examines the elements that make up the data stream
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in the example.</p>
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<div class="section"><p>The example in <a href="rbal1interpretdata.htm#rbal1interpretdata__rbal1rwinf">Figure 1</a> shows
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the data stream received during a distributed SQL query function. This particular
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trace was run at the application requester (AR) end of the connection. Therefore,
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the associated program module that produced the data is QRWSQRY.</p>
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</div>
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<div class="section"><p>For more information about the interpretation of Distributed
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Relational Database Architecture™ (DRDA<sup>®</sup>) data streams, see the <cite>Distributed
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Relational Database Architecture Reference</cite> and the <cite>Distributed
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Data Management Level 4.0 Architecture Reference</cite> books. These documents
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are available on the Web at <a href="http://www.opengroup.org/dbiop/index.htm" target="_blank">www.opengroup.org/dbiop/index.htm</a>.</p>
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</div>
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<div class="section"><p>The trace data follows the colon (:) marking the end of the trace
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point identifier. In this example, the first six bytes of the data stream
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contain the DDM data stream structure (DSS) header. The first two bytes of
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this DSS header are a length field. The third byte, <span>X'D0'</span> is the
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registered SNA architecture identifier for all DDM data. The fourth byte is
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the format identifier (explained in more detail later). The fifth and sixth
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bytes contain the DDM request correlation identifier.</p>
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</div>
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<div class="section"><p>The next two bytes, <span>X'0010'</span> (decimal 16) give the length
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of the next DDM object, which in this case is identified by the <span>X'2205'</span> which
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follows it and is the code point for the OPNQRYRM reply message.</p>
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</div>
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<div class="section"><p>Following the 16-byte reply message is a six-byte DSS header for
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the reply objects that follow the reply message. The first reply object is
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identified by the <span>X'241A'</span> code point. It is a QRYDSC object. The
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second reply object in the example is a QRYDTA structure identified by the <span>X'241B'</span> code
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point (split between two lines in the trace output). As with the OPNQRYRM
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code point, the preceding two bytes give the length of the object.</p>
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</div>
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<div class="section"><p>Looking more closely at the QRYDTA object, you can see a <span>X'FF'</span> following
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the <span>X'241B'</span> code point. This represents a null SQLCAGRP (the form
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of an SQLCA or SQL diagnostic area that flows on the wire). The null form
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of the SQLCAGRP indicates that it contains no error or warning information
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about the associated data. In this case, the associated data is the row of
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data from an SQL SELECT operation. It follows the null SQLCAGRP. Because rows
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of data as well as SQLCAGRPs are nullable, however, the first byte that follows
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the null SQLCAGRP is an indicator containing <span>X'00'</span> that indicates
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that the row of data is not null. The meaning of the null indicator byte is
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determined by the first bit. A 1 in this position indicates null. However,
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all 8 bits are usually set on when an indicator represents a null object.</p>
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</div>
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<div class="section"><p>The format of the row of data is indicated by the preceding QRYDSC
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object. In this case, the QRYDSC indicates that the row contains a nullable
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SMALLINT value, a nullable CHAR(3) value, and a non-nullable double precision
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floating point value. The second byte past the null SQLCAGRP is the null indicator
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associated with the SMALLINT field. It indicates the field is not null, and
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the <span>X'0001'</span> following it is the field data. The nullable CHAR(3)
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that follows is present and contains 111. The floating point value that follows
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next does not have a <span>X'00'</span> byte following it, since it is defined
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to be not nullable.</p>
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</div>
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<div class="section"><p>A second row of data with a null SQLCAGRP follows the first, which
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in turn is followed by another six-byte DSS header. The second half of the
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format byte (<span>X'2'</span>) contained in that header indicates that the corresponding
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DSS is a REPLY. The format byte of the previous DSS (<span>X'53'</span>) indicated
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that it was an OBJECT DSS. The ENDQRYRM reply message carried by the third
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DSS requires that it be contained in a REPLY DSS. The ENDQRYRM code point
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is <span>X'220B'</span>. This reply message contains a severity code of <span>X'0004'</span>,
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and the name of the RDB that returned the query data ('DB2ESYS').</p>
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</div>
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<div class="section"><p>Following the third DSS in this example is a fourth and final
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one. The format byte of it is <span>X'03'</span>. The 3 indicates that it is an
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OBJECT DSS, and the 0 that precedes it indicates that it is the last DSS of
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the chain (the chaining bits are turned off).</p>
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</div>
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<div class="section"><p>The object in this DSS is an SQLCARD containing a non-null SQLCAGRP.
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The first byte following the <span>X'2408'</span> SQLCARD code point is the indicator
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telling us that the SQLCAGRP is not null. The next four bytes, <span>X'00000064'</span>,
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represents the +100 SQLCODE which means that the query was ended by the encounter
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of a 'row not found' condition. The rest of the fields correspond to other
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fields in an SQLCA. The rest of the fields correspond to other fields in an
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SQLCA or SQL diagnostic area. The mapping of SQLCAGRP fields to SQLCA and
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SQL diagnostic area fields can be found in the <cite>Distributed
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Relational Database Architecture Reference</cite> book. This document
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is available at the Open Group Web site <img src="www.gif" alt="Link outside information center" /><a href="http://www.opengroup.org/dbiop/index.htm" target="_blank">(www.opengroup.org/dbiop/index.htm)</a></p>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbal1interpretdata.htm" title="The RW component of the i5/OS licensed program includes most of the Distributed Relational Database Architecture (DRDA) support.">Interpret data entries for the RW component of trace job</a></div>
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</div>
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</div>
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</body>
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</html>
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