title: Why does DB2 suggest one table per tablespace?
body: <p>The DB2 docs for DB2/z v10 have the following snippet in the <a href="http://publib.boulder.ibm.com/infocenter/dzichelp/v2r2/index.jsp?topic=/com.ibm.db2z10.doc.intro/src/tpc/db2z_tablespaces.htm" rel="nofollow">tablespaces section</a>:</p>
  
  <blockquote>
    <p>As a general rule, you should have only one table in each table space.</p>
  </blockquote>
  
  <p>But it doesn't actually provide any rationale for this.</p>
  
  <p>We have some tables storing historical time-based information along the following lines (greatly reduced in complexity but should be enough to illustrate):</p>
  
  <pre><code>Table HOURLY_CPU_USAGE:
      RecDate        date
      RecTime        time
      Node           char(32)
      MaxCpuUsage    float
      primary key    (RecDate, RecTime, Node)
  Table DAILY_CPU_USAGE:
      RecDate        date
      Node           char(32)
      MaxCpuUsage    float
      primary key    (RecDate, Node)
  Table MONTHLY_CPU_USAGE:
      RecDate        date
      Node           char(32)
      MaxCpuUsage    float
      primary key    (RecDate, Node)
  </code></pre>
  
  <p>(the daily table has all the hourly records rolled up into a single day, and the monthly table does the same with the daily data, rolling it up into the row with date <code>YYYY-MM-01</code>).</p>
  
  <p>Now it seems to me that this tables are all very similar in purpose and I'm not certain <em>why</em> we'd want to keep them in separate tablespaces.</p>
  
  <p>Discount for now the possibility of combining them into a single table, that's a suggestion I've made but there are complications preventing it.</p>
  
  <p>What <em>is</em> the rationale behind the "one table per tablespace" guideline? What are the exceptions, if any? I'm assuming they're <em>may</em> be exceptions since it seems very much a guideline rather than a hard-and-fast rule.</p>