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From: Ali Akhtar <ali.rac200@gmail.com>
Date: Sat, 12 Nov 2016 16:26:05 +0500
Message-ID: <CAKiMtbd2boE9qDZR8Q6-t53NnYrc95eC8KwES_Sw5r9naz1=nw@mail.gmail.com>
Subject: Re: Consistency when adding data to collections concurrently?
To: user@cassandra.apache.org
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archived-at: Sat, 12 Nov 2016 11:26:13 -0000

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I'm responding to a 3rd party API, so I have no control over sending the
labels together instead of one by one. In this case, the API will send them
one by one.

The list is actually of a list<frozen<my_udt>> and not a text (I used text
for simplification, apologies).

In that case, will updates still merge the list values instead of
overwriting them?

On Sat, Nov 12, 2016 at 4:15 PM, Oskar Kjellin <oskar.kjellin@gmail.com>
wrote:

> Could you not send both labels in one request? Race conditions should
> still be handled as Vladimir suggests. But in this specific case the client
> could send both as 1 request thus simplifying the solution.
>
> /Oskar
>
> On 12 nov. 2016, at 12:05, Vladimir Yudovin <vladyu@winguzone.com> wrote:
>
> Hi Ali,
>
> >What can I do so I end up with [1, 2] instead of either [1] or [2] after
> both requests have been processed?
> Use UPDATE, not INSERT. Thus new labels will be added to list, without
> overwriting old ones. Also consider usage of SET instead of LIST to avoid
> duplicates.
>
> Best regards, Vladimir Yudovin,
>
> *Winguzone <https://winguzone.com?from=list> - Hosted Cloud
> CassandraLaunch your cluster in minutes.*
>
>
> ---- On Sat, 12 Nov 2016 05:34:24 -0500*Ali Akhtar <ali.rac200@gmail.com
> <ali.rac200@gmail.com>>* wrote ----
>
> I have a table where each record contains a list<string> of labels.
>
> I have an endpoint which responds to new labels being added to a record by
> the user.
>
> Consider the following scenario:
>
> - Record X, labels = []
> - User selects 2 labels, clicks a button, and 2 http requests are
> generated.
> - The server receives request for Label 1 and Label 2 at the same time.
> - Both requests see the labels as empty, add 1 label to the collection,
> and send it.
> - Record state as label 1 request sees it: [1], as label 2 sees it: [2]
>
> How will the above conflict be resolved? What can I do so I end up with
> [1, 2] instead of either [1] or [2] after both requests have been processed?
>
>
>

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<div dir=3D"ltr">I&#39;m responding to a 3rd party API, so I have no contro=
l over sending the labels together instead of one by one. In this case, the=
 API will send them one by one.<div><br></div><div>The list is actually of =
a list&lt;frozen&lt;my_udt&gt;&gt; and not a text (I used text for simplifi=
cation, apologies).</div><div><br></div><div>In that case, will updates sti=
ll merge the list values instead of overwriting them?</div></div><div class=
=3D"gmail_extra"><br><div class=3D"gmail_quote">On Sat, Nov 12, 2016 at 4:1=
5 PM, Oskar Kjellin <span dir=3D"ltr">&lt;<a href=3D"mailto:oskar.kjellin@g=
mail.com" target=3D"_blank">oskar.kjellin@gmail.com</a>&gt;</span> wrote:<b=
r><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:=
1px #ccc solid;padding-left:1ex"><div dir=3D"auto"><div>Could you not send =
both labels in one request? Race conditions should still be handled as Vlad=
imir suggests. But in this specific case the client could send both as 1 re=
quest thus simplifying the solution.=C2=A0</div><span class=3D"HOEnZb"><fon=
t color=3D"#888888"><div id=3D"m_-3663432121659418903AppleMailSignature"><b=
r>/Oskar</div></font></span><div><div class=3D"h5"><div><br>On 12 nov. 2016=
, at 12:05, Vladimir Yudovin &lt;<a href=3D"mailto:vladyu@winguzone.com" ta=
rget=3D"_blank">vladyu@winguzone.com</a>&gt; wrote:<br><br></div><blockquot=
e type=3D"cite"><div><div style=3D"font-size:10pt;font-family:Verdana,Arial=
,Helvetica,sans-serif"><div>Hi Ali,<br></div><div><br></div><div>&gt;What c=
an I do so I end up with [1, 2] instead of either [1] or [2] after both req=
uests have been processed?<br></div><div>Use UPDATE, not INSERT. Thus new l=
abels will be added to list, without overwriting old ones. Also consider us=
age of SET instead of LIST to avoid duplicates.=C2=A0 <br></div><div><br></=
div><div id=3D"m_-3663432121659418903"><div>Best regards, Vladimir Yudovin,=
 <br></div><div><i><a href=3D"https://winguzone.com?from=3Dlist" target=3D"=
_blank">Winguzone</a> - Hosted Cloud Cassandra<br>Launch your cluster in mi=
nutes.</i></div></div><div><br></div><div class=3D"m_-3663432121659418903zm=
ail_extra"><div id=3D"m_-36634321216594189031"><div><br></div><div>---- On =
Sat, 12 Nov 2016 05:34:24 -0500<b>Ali Akhtar &lt;<a href=3D"mailto:ali.rac2=
00@gmail.com" target=3D"_blank">ali.rac200@gmail.com</a>&gt;</b> wrote ----=
<br></div></div><div><br></div><blockquote style=3D"border-left:1px solid #=
cccccc;padding-left:6px;margin:0 0 0 5px"><div><div dir=3D"ltr"><div>I have=
 a table where each record contains a list&lt;string&gt; of labels.<br></di=
v><div><br></div><div>I have an endpoint which responds to new labels being=
 added to a record by the user.<br></div><div><br></div><div>Consider the f=
ollowing scenario:<br></div><div><br></div><div>- Record X, labels =3D []<b=
r></div><div>- User selects 2 labels, clicks a button, and 2 http requests =
are generated.<br></div><div>- The server receives request for Label 1 and =
Label 2 at the same time.<br></div><div>- Both requests see the labels as e=
mpty, add 1 label to the collection, and send it.<br></div><div>- Record st=
ate as label 1 request sees it: [1], as label 2 sees it: [2]<br></div><div>=
<br></div><div>How will the above conflict be resolved? What can I do so I =
end up with [1, 2] instead of either [1] or [2] after both requests have be=
en processed?<br></div></div></div></blockquote></div><div><br></div></div>=
</div></blockquote></div></div></div></blockquote></div><br></div>

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