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<title>Implementation and optimization of a single file query with DB2 Multisystem</title>
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<h1 class="topictitle1">Implementation and optimization of a single file query with DB2<sup>®</sup> Multisystem</h1>
<div><p>To do a single file query, the system where the query was specified,
the coordinator node, determines the nodes of the file to which to send the
query. Those nodes run the query and return the queried records to the coordinator
node.</p>
<div class="section"><p>All of the examples in this chapter use the following distributed files:
DEPARTMENT and EMPLOYEE. The node group for these files consists of SYSA,
SYSB, and SYSC. The data is partitioned on the department number.</p>
<div class="p">The
following SQL statement creates the DEPARTMENT distributed file. <pre>CREATE TABLE DEPARTMENT
(DEPTNO CHAR(3) NOT NULL,
DEPTNAME VARCHAR(20) NOT NULL,
MGRNO CHAR(6),
ADMRDEPT CHAR(3) NOT NULL)
IN NODGRP1 PARTITIONING KEY(DEPTNO)</pre>
</div>
<table cellpadding="4" cellspacing="0" border="1" class="tableborder"><tr><td>
<table cellpadding="4" cellspacing="0" summary="" border="0"><caption>Table 1. DEPARTMENT table</caption><thead align="left"><tr><th align="center" valign="bottom" width="11.923076923076923%" id="d0e54">Node</th>
<th align="center" valign="bottom" width="13.846153846153847%" id="d0e56">Record number</th>
<th align="center" valign="bottom" width="15.96153846153846%" id="d0e58">DEPTNO</th>
<th align="left" valign="bottom" width="20.192307692307693%" id="d0e60">DEPTNAME</th>
<th align="center" valign="bottom" width="17.884615384615383%" id="d0e62">MGRNO</th>
<th align="center" valign="bottom" width="20.192307692307693%" id="d0e64">ADMRDEPT</th>
</tr>
</thead>
<tbody><tr><td align="center" valign="top" width="11.923076923076923%" headers="d0e54 ">SYSA</td>
<td align="center" valign="top" width="13.846153846153847%" headers="d0e56 ">1</td>
<td align="center" valign="top" width="15.96153846153846%" headers="d0e58 ">A00</td>
<td align="left" valign="top" width="20.192307692307693%" headers="d0e60 ">Support services</td>
<td align="center" valign="top" width="17.884615384615383%" headers="d0e62 ">000010</td>
<td align="center" valign="top" width="20.192307692307693%" headers="d0e64 ">A00</td>
</tr>
<tr><td align="center" valign="top" width="11.923076923076923%" headers="d0e54 ">SYSB</td>
<td align="center" valign="top" width="13.846153846153847%" headers="d0e56 ">2</td>
<td align="center" valign="top" width="15.96153846153846%" headers="d0e58 ">A01</td>
<td align="left" valign="top" width="20.192307692307693%" headers="d0e60 ">Planning</td>
<td align="center" valign="top" width="17.884615384615383%" headers="d0e62 ">000010</td>
<td align="center" valign="top" width="20.192307692307693%" headers="d0e64 ">A00</td>
</tr>
<tr><td align="center" valign="top" width="11.923076923076923%" headers="d0e54 ">SYSC</td>
<td align="center" valign="top" width="13.846153846153847%" headers="d0e56 ">3</td>
<td align="center" valign="top" width="15.96153846153846%" headers="d0e58 ">B00</td>
<td align="left" valign="top" width="20.192307692307693%" headers="d0e60 ">Accounting</td>
<td align="center" valign="top" width="17.884615384615383%" headers="d0e62 ">000050</td>
<td align="center" valign="top" width="20.192307692307693%" headers="d0e64 ">B00</td>
</tr>
<tr><td align="center" valign="top" width="11.923076923076923%" headers="d0e54 ">SYSA</td>
<td align="center" valign="top" width="13.846153846153847%" headers="d0e56 ">4</td>
<td align="center" valign="top" width="15.96153846153846%" headers="d0e58 ">B01</td>
<td align="left" valign="top" width="20.192307692307693%" headers="d0e60 ">Programming</td>
<td align="center" valign="top" width="17.884615384615383%" headers="d0e62 ">000050</td>
<td align="center" valign="top" width="20.192307692307693%" headers="d0e64 ">B00</td>
</tr>
</tbody>
</table>
</td></tr></table>
<div class="p">The following SQL statement creates the EMPLOYEE distributed file.
<pre>CREATE TABLE EMPLOYEE
(EMPNO CHAR(6) NOT NULL,
FIRSTNME VARCHAR(12) NOT NULL,
LASTNAME VARCHAR(15) NOT NULL,
WORKDEPT CHAR(3) NOT NULL,
JOB CHAR(8),
SALARY DECIMAL(9,2))
IN NODGRP1 PARTITIONING KEY(WORKDEPT)</pre>
</div>
<table cellpadding="4" cellspacing="0" border="1" class="tableborder"><tr><td>
<table cellpadding="4" cellspacing="0" summary="" width="100%" border="0"><caption>Table 2. EMPLOYEE table</caption><thead align="left"><tr><th align="center" valign="bottom" width="7.894736842105263%" id="d0e137">Node</th>
<th align="center" valign="bottom" width="13.157894736842104%" id="d0e139">Record number</th>
<th align="center" valign="bottom" width="13.157894736842104%" id="d0e141">EMPNO</th>
<th align="left" valign="bottom" width="13.157894736842104%" id="d0e143">FIRSTNME</th>
<th align="left" valign="bottom" width="13.157894736842104%" id="d0e145">LASTNAME</th>
<th align="center" valign="bottom" width="13.157894736842104%" id="d0e147">WORK DEPT</th>
<th align="left" valign="bottom" width="13.157894736842104%" id="d0e149">JOB</th>
<th align="center" valign="bottom" width="13.157894736842104%" id="d0e151">SALARY</th>
</tr>
</thead>
<tbody><tr><td align="center" valign="top" width="7.894736842105263%" headers="d0e137 ">SYSA</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e139 ">1</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e141 ">000010</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e143 ">Christine</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e145 ">Haas</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e147 ">A00</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e149 ">Manager</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e151 ">41250</td>
</tr>
<tr><td align="center" valign="top" width="7.894736842105263%" headers="d0e137 ">SYSA</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e139 ">2</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e141 ">000020</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e143 ">Sally</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e145 ">Kwan</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e147 ">A00</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e149 ">Clerk</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e151 ">25000</td>
</tr>
<tr><td align="center" valign="top" width="7.894736842105263%" headers="d0e137 ">SYSB</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e139 ">3</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e141 ">000030</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e143 ">John</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e145 ">Geyer</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e147 ">A01</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e149 ">Planner</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e151 ">35150</td>
</tr>
<tr><td align="center" valign="top" width="7.894736842105263%" headers="d0e137 ">SYSB</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e139 ">4</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e141 ">000040</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e143 ">Irving</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e145 ">Stern</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e147 ">A01</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e149 ">Clerk</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e151 ">32320</td>
</tr>
<tr><td align="center" valign="top" width="7.894736842105263%" headers="d0e137 ">SYSC</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e139 ">5</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e141 ">000050</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e143 ">Michael</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e145 ">Thompson</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e147 ">B00</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e149 ">Manager</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e151 ">38440</td>
</tr>
<tr><td align="center" valign="top" width="7.894736842105263%" headers="d0e137 ">SYSC</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e139 ">6</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e141 ">000060</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e143 ">Eileen</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e145 ">Henderson</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e147 ">B00</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e149 ">Accountant</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e151 ">33790</td>
</tr>
<tr><td align="center" valign="top" width="7.894736842105263%" headers="d0e137 ">SYSA</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e139 ">7</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e141 ">000070</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e143 ">Jennifer</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e145 ">Lutz</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e147 ">B01</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e149 ">Programmer</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e151 ">42325</td>
</tr>
<tr><td align="center" valign="top" width="7.894736842105263%" headers="d0e137 ">SYSA</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e139 ">8</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e141 ">000080</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e143 ">David</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e145 ">White</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e147 ">B01</td>
<td align="left" valign="top" width="13.157894736842104%" headers="d0e149 ">Programmer</td>
<td align="center" valign="top" width="13.157894736842104%" headers="d0e151 ">36450</td>
</tr>
</tbody>
</table>
</td></tr></table>
<p>What follows is a query using the above defined distributed file
EMPLOYEE, with index EMPIDX created over the field SALARY. The query is entered
on SYSA.</p>
<p>SQL statement:</p>
<pre> SELECT * FROM EMPLOYEE WHERE SALARY &gt; 40000
</pre>
<p>OPNQRYF command:</p>
<pre> OPNQRYF FILE((EMPLOYEE)) QRYSLT('SALARY &gt; 40000')</pre>
<p>In
this case, SYSA sends the above query to all the nodes of EMPLOYEE, including
SYSA. Each node runs the query and returns the records to SYSA. Because a
distributed index exists on field SALARY of file EMPLOYEE, optimization that
is done on each node decides whether to use the index.</p>
<p>In the next example,
the query is specified on SYSA, but the query is sent to a subset of the nodes
where the EMPLOYEE file exists. In this case, the query is run locally on
SYSA only.</p>
<p>SQL statement:</p>
<pre> SELECT * FROM EMPLOYEE WHERE WORKDEPT = 'A00'</pre>
<p>OPNQRYF command:</p>
<pre> OPNQRYF FILE((EMPLOYEE)) QRYSLT('WORKDEPT = 'A00')</pre>
<p>The distributed query optimizer determines that
there is an isolatable record selection, WORKDEPT = 'A00', involving the partitioning
key, WORKDEPT, for this query. The optimizer hashes the value 'A00' and based
on the hash value, finds the node at which all of the records satisfying this
condition are located. In this case, all of the records satisfying this condition
are on SYSA, thus the query is sent only to that node. Because the query originated
on SYSA, the query is run locally on SYSA.</p>
<p>The following conditions
subset the number of nodes at which a query runs:</p>
<ul><li>All fields of the partitioning key must be isolatable record selection</li>
<li>All predicates must use the equal (=) operator</li>
<li>All fields of the partitioning key must be compared to a
literal</li>
</ul>
<div class="note"><span class="notetitle">Note:</span> For performance reasons, you should specify record selection predicates
that match the partitioning key in order to direct the query to a particular
node. Record selection with scalar functions of NODENAME, PARTITION, and NODENUMBER
can also direct the query to specific nodes.</div>
</div>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="qqp.htm" title="This topic provides you with some guidelines for designing queries so that they use query resources more efficiently when you run queries that use distributed files.">Query design for performance with DB2 Multisystem</a></div>
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