I doesn't realized postgresql can be such clever.<br /><br />Another problem I just found is after one tuple is
deleted,there will be some slots unoccupied. The offset cannot be computed even know how much tuples a page can
contain.<br/><br />I need one hash table.<br /><br />Thanks<br />--<br />Pei<br /><br /><div class="gmail_quote">On
Tue,Sep 21, 2010 at 8:47 PM, Kevin Grittner <span dir="ltr"><<a
href="mailto:Kevin.Grittner@wicourts.gov">Kevin.Grittner@wicourts.gov</a>></span>wrote:<br /><blockquote
class="gmail_quote"style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left:
1ex;"><divclass="im">Pei He wrote:<br /><br /> > The offset is the order of a tuple in a Sequential Scan.<br /><br
/></div>That'snot a safe assumption. Try starting a sequential scan against<br /> a large table on one connection;
thenbefore it finishes, start the<br /> same query on another connection. The second query joins the one<br /> already
inprogress and then starts over, "wrapping around".<br /><font color="#888888"><br /> -Kevin<br
/></font></blockquote></div><br/>