Re: polyphase merge?

Hmm probably it's worth to try this. Has anybody try this before? If not, I am interested to give it a try.<br /><br
/>Regards,<br/><br />Don<br /><br /><div class="gmail_quote">On Wed, Feb 4, 2009 at 11:25 PM, Gregory Stark <span
dir="ltr"><<ahref="mailto:stark@enterprisedb.com">stark@enterprisedb.com</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;"><divclass="Ih2E3d">Simon Riggs <simon@2ndQuadrant.com> writes:<br /><br /> > On Wed, 2009-02-04 at 10:55
+0000,Greg Stark wrote:<br /> >> Is this basically the same as our current algorithm but without<br /> >>
multiplexingthe tapes onto single files? I have been wondering<br /> >> whether we multiplex the tapes any better
thanfilesystems can lay out<br /> >> separate files actually.<br /> ><br /> > I don't think you'll be able
todo that more efficiently than we already<br /> > do. Read the top of tuplesort.c<br /><br /></div>Huh?<br /><br />
Thequestion I posed was whether we do it any better than filesystems do, not<br /> whether we could do a better job. If
filesystemscan do as good a job then we<br /> might as well create separate files for each tape and let the
filesystem<br/> decide where to allocate space. That would mean we could massively simplify<br /> logtape.c and just
createa separate file for every tape.<br /><br /> Possible reasons that filesystems could do better than us are that
theyhave<br /> access to more information about actual storage layout on disk, that they have<br /> more information
abouthardware characteristics, and that it would give the<br /> filesystem cache a better idea of the access pattern
whichlogtape.c might be<br /> confusing the picture of currently.<br /><br /> On the other hand possible reasons why
filesystemswould suck at this include<br /> creating and deleting new files being a slow or locking operation on
many<br/> filesystems, and dealing with directories of large numbers of files being<br /> poorly optimized on
others.<br/><font color="#888888"><br /> --<br />  Gregory Stark<br />  EnterpriseDB          <a
href="http://www.enterprisedb.com"target="_blank">http://www.enterprisedb.com</a><br />  Ask me about EnterpriseDB's
RemoteDBAservices!<br /></font></blockquote></div><br />