Re: [MonetDB-users] Searching for possibilities to reduce the fluctuation in insertion times.

2 Feb 2009

      Hi,

by insertion of the document, you are referring to shredding (aka.
pf:add-doc) and not inserting (updating) with new elements on the
already shredded document, right?

What kind of I/O is the system doing? You mean an I/O originated from
some other process that just take up all the resources of your system?
(like copying some hundreds of gigs data to the disk?) If that is the
case, then the problem is just from the OS and the scheduling
algorithms that uses for managing I/O requests. On the other hand, if
this I/O is started because of shredding this small XML document, then
that should not happen. Do you shredded as an updatable document? How
full is your disk? It might be because of large fragmentation on the
disk and not enough free space.

lefteris

On Mon, Feb 2, 2009 at 10:15 AM, John van Schie (DT)  wrote:
...
Hi,
We use MonetDB v4.26.4 (Nov 2008-sp2) for our application with the
XQuery frontend. Often, queries are executed very fast, but sometimes,
execution of the same query takes significantly more time.
For example:
We insert a XML document of 1.4Mb. with a maximum depth of 4. The
document is structured as follows:
<rootelement>
 <item>
  <child1>
    <sha1>sha1-value</sha1>
    <md5>md5-value</md5>
  </child1>
 </item>
 ...
</rootelement>
We have 8k 'item' elements.
Often the insertion of this document is performed in ~0.5s, which is
fine. But when the system is performing IO (e.g. copying a large file),
the insertion can take up to 6 minutes.
So I have two questions:
1) What is the cause of this large difference in execution times;
2) Is there a way to configure MonetDB (or the server) in such a way
that the difference between the 'fast' and 'slow' is smaller.
Regards,
John van Schie
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Re: [MonetDB-users] Searching for possibilities to reduce the fluctuation in insertion times.

Lefteris