Re: Block nested loop join

<div dir="ltr">Dear All,<br /><br /> I took a look at the source code for hash join this morning and I realized that
theblock nested loop join is somewhat similar to that. <br /><br /> Thanks for the discussions. <br /><br /> Bramandia
R.<br/><br /><div class="gmail_quote">On Fri, Oct 10, 2008 at 8:19 PM, Tom Lane <span dir="ltr"><<a
href="mailto:tgl@sss.pgh.pa.us">tgl@sss.pgh.pa.us</a>></span>wrote:<br /><blockquote class="gmail_quote"
style="border-left:1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div
class="Ih2E3d">GregoryStark <<a href="mailto:stark@enterprisedb.com">stark@enterprisedb.com</a>> writes:<br />
>So the use case of a real block nested loop would be doing a cartesian join of<br /> > two large tables where
neitherfits in RAM. That does seem like it might be<br /> > kind of narrow given how large the output would be.<br
/><br/></div>Yeah.  If you have a hashable join condition then our existing batched<br /> hash join code should be
roughlyequivalent to this method.  So the use<br /> case is joining a couple of large tables with an un-hashable,<br />
un-indexablejoin condition (or none at all, ie cross product) and that<br /> just isn't something we hear people
wantingto do a lot.  I can't really<br /> see why we'd bother maintaining extra code for block nested loop.<br /><br />
                      regards, tom lane<br /></blockquote></div><br /></div>