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Date: Mon, 8 Mar 2010 10:07:54 -0800
Message-ID: <74f4d40b1003081007l2dbe5bd1o8327523f2d984ca@mail.gmail.com>
Subject: Re: Reason for not allowing null values for in Column
From: Erik Holstad <erikholstad@gmail.com>
To: cassandra-user@incubator.apache.org
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On Mon, Mar 8, 2010 at 9:30 AM, Jonathan Ellis <jbellis@gmail.com> wrote:

> On Mon, Mar 8, 2010 at 11:22 AM, Erik Holstad <erikholstad@gmail.com>
> wrote:
> > I was probably a little bit unclear here. I'm wondering about the two
> byte[]
> > in Column.
> > One for name and one for value. I was under the impression that the
> > skiplistmap
> > wraps the Columns, not that the name and the value are themselves
> inserted
> > into a map?
>
> The column name is the key in one such map, yes.
>
So why is it again that the value field in the Column cannot be null if it
is not the
value field in the map, but just a part of the value field?

>
> >> > is it really that expensive to check if the list is empty before
> >> > returning
> >> > that row
> >>
> >> Yes, because you have to check the entire row, which may be much
> >> larger than the given predicate.
> >
> > That makes sense, but why would you be interested in the rows present
> > outside
> > your specified predicate?
>
> Because get_range_slice says, "apply this predicate to the range of
> rows given," meaning, if the predicate result is empty, we have to
> include an empty result for that row key.  It is perfectly valid to
> perform such a query returning empty column lists for some or all
> keys, even if no deletions have been performed.  So to special case
> leaving out result entries for deletions, we have to check the entire
> rest of the row to make sure there is no undeleted data anywhere else
> either (in which case leaving the key out would be an error).
>
All of this makes total sense, I'm wondering about use cases where you want
to
get an empty row when you don't know if it has been deleted or not.


-- 
Regards Erik

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<br><br><div class=3D"gmail_quote">On Mon, Mar 8, 2010 at 9:30 AM, Jonathan=
 Ellis <span dir=3D"ltr">&lt;<a href=3D"mailto:jbellis@gmail.com">jbellis@g=
mail.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" style=
=3D"border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; p=
adding-left: 1ex;">
<div class=3D"im">On Mon, Mar 8, 2010 at 11:22 AM, Erik Holstad &lt;<a href=
=3D"mailto:erikholstad@gmail.com">erikholstad@gmail.com</a>&gt; wrote:<br>
&gt; I was probably a little bit unclear here. I&#39;m wondering about the =
two byte[]<br>
&gt; in Column.<br>
&gt; One for name and one for value. I was under the impression that the<br=
>
&gt; skiplistmap<br>
&gt; wraps the Columns, not that the name and the value are themselves inse=
rted<br>
&gt; into a map?<br>
<br>
</div>The column name is the key in one such map, yes.<br></blockquote><div=
>So why is it again that the value field in the Column cannot be null if it=
 is not the<br>value field in the map, but just a part of the value field? =
<br>
</div><blockquote class=3D"gmail_quote" style=3D"border-left: 1px solid rgb=
(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class=3D"im"><br>
&gt;&gt; &gt; is it really that expensive to check if the list is empty bef=
ore<br>
&gt;&gt; &gt; returning<br>
&gt;&gt; &gt; that row<br>
&gt;&gt;<br>
&gt;&gt; Yes, because you have to check the entire row, which may be much<b=
r>
&gt;&gt; larger than the given predicate.<br>
&gt;<br>
&gt; That makes sense, but why would you be interested in the rows present<=
br>
&gt; outside<br>
&gt; your specified predicate?<br>
<br>
</div>Because get_range_slice says, &quot;apply this predicate to the range=
 of<br>
rows given,&quot; meaning, if the predicate result is empty, we have to<br>
include an empty result for that row key. =A0It is perfectly valid to<br>
perform such a query returning empty column lists for some or all<br>
keys, even if no deletions have been performed. =A0So to special case<br>
leaving out result entries for deletions, we have to check the entire<br>
rest of the row to make sure there is no undeleted data anywhere else<br>
either (in which case leaving the key out would be an error).<br>
</blockquote></div>All of this makes total sense, I&#39;m wondering about u=
se cases where you want to <br>get an empty row when you don&#39;t know if =
it has been deleted or not.<br><br clear=3D"all"><br>-- <br>Regards Erik<br=
>


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