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From: Ali Akhtar <ali.rac200@gmail.com>
Date: Sat, 12 Nov 2016 17:06:03 +0500
Message-ID: <CAKiMtbe34PkFATB46J4GBgod1KeSRfXucmWsfMo2ZPptMnFPQQ@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 12:06:15 -0000

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Thanks DuyHai, I will switch to using a set.

But I'm still not sure how to resolve the original question.

- Original labels = []
- Request 1 arrives with label = 1, and request 2 arrives with label = 2
- Updates are sent to c* with labels = [1] and labels = [2] simultaneously.

What will happen in the above case? Will it cause the labels to end up as
[1,2] (what I want) or either [1] or [2]?

If I use consistency level = all, will that cause it to end up with [1,2]?

On Sat, Nov 12, 2016 at 4:59 PM, DuyHai Doan <doanduyhai@gmail.com> wrote:

> Don't use list, use set instead. If you need ordering of insertion, use a
> map<timeuuid,text> where timeuuid is generated by the client to guarantee
> insertion order
>
> When setting a new value to a list, C* will do a read-delete-write
> internally e.g. read the current list, remove all its value (by a range
> tombstone) and then write the new list. Please note that prepend & append
> operations on list do not require this read-delete-write and thus performs
> slightly better
>
> On Sat, Nov 12, 2016 at 11:34 AM, Ali Akhtar <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">Thanks=C2=A0DuyHai, I will switch to using a set.<div><br>=
</div><div>But I&#39;m still not sure how to resolve the original question.=
</div><div><br></div><div>- Original labels =3D []</div><div>- Request 1 ar=
rives with label =3D 1, and request 2 arrives with label =3D 2</div><div>- =
Updates are sent to c* with labels =3D [1] and labels =3D [2] simultaneousl=
y.</div><div><br></div><div>What will happen in the above case? Will it cau=
se the labels to end up as [1,2] (what I want) or either [1] or [2]?</div><=
div><br></div><div>If I use consistency level =3D all, will that cause it t=
o end up with [1,2]?</div></div><div class=3D"gmail_extra"><br><div class=
=3D"gmail_quote">On Sat, Nov 12, 2016 at 4:59 PM, DuyHai Doan <span dir=3D"=
ltr">&lt;<a href=3D"mailto:doanduyhai@gmail.com" target=3D"_blank">doanduyh=
ai@gmail.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" sty=
le=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div d=
ir=3D"ltr">Don&#39;t use list, use set instead. If you need ordering of ins=
ertion, use a map&lt;timeuuid,text&gt; where timeuuid is generated by the c=
lient to guarantee insertion order<div><br></div><div>When setting a new va=
lue to a list, C* will do a read-delete-write internally e.g. read the curr=
ent list, remove all its value (by a range tombstone) and then write the ne=
w list. Please note that prepend &amp; append operations on list do not req=
uire this read-delete-write and thus performs slightly better</div></div><d=
iv class=3D"HOEnZb"><div class=3D"h5"><div class=3D"gmail_extra"><br><div c=
lass=3D"gmail_quote">On Sat, Nov 12, 2016 at 11:34 AM, Ali Akhtar <span dir=
=3D"ltr">&lt;<a href=3D"mailto:ali.rac200@gmail.com" target=3D"_blank">ali.=
rac200@gmail.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote"=
 style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><d=
iv dir=3D"ltr">I have a table where each record contains a list&lt;string&g=
t; of labels.<div><br></div><div>I have an endpoint which responds to new l=
abels being added to a record by the user.</div><div><br></div><div>Conside=
r the following scenario:</div><div><br></div><div>- Record X, labels =3D [=
]</div><div>- User selects 2 labels, clicks a button, and 2 http requests a=
re generated.</div><div>- The server receives request for Label 1 and Label=
 2 at the same time.</div><div>- Both requests see the labels as empty, add=
 1 label to the collection, and send it.</div><div>- Record state as label =
1 request sees it: [1], as label 2 sees it: [2]</div><div><br></div><div>Ho=
w 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?</di=
v></div>
</blockquote></div><br></div>
</div></div></blockquote></div><br></div>

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