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From "Hiller, Dean" <Dean.Hil...@nrel.gov>
Subject Re: Correct model
Date Wed, 19 Sep 2012 20:33:01 GMT
Uhm, unless I am mistaken, a NEW request implies a new UUID so you can just write it to both
the index to the request row and to the user that request was for all in one shot with no
need to read, right?

(Also, read before write is not necessarily bad…it really depends on your situation but
in this case, I don't think you need read before write).

For your structured data comment….
Actually playOrm stores structured and unstructured data.  It follows the pattern cassandra
is adopting more and more of "partial" schemas and plans to hold to that path.  It is a complete
break from JPA due to noSQL being so different.

and each request would have its own id, right

Yes, in my design, I choose each request with it's own id.

Wouldn't it be faster to have a composite key in the requestCF itself?

In CQL, don't you have to have an == in the first part of the clause meaning you would have
to select the user id, BUT you wanted requests > date no matter which user so the indices
I gave you have that information with a simple column slice of the data.  The indices I gave
you look like this(composite column names)…. <time1>.<req1>.<user1>, <time2>.<req2>.<user1>,
<time3>.<req3>.<user2>  NOTE that each is a UUID there in the <> so
are unique.

Maybe there is a way, but I am not sure on how to get all the latest request > data for
every user….I guess you could always map/reduce but that is generally reserved for analytics
or maybe updating new index tables you are creating for reading faster.

Later,
Dean

From: Marcelo Elias Del Valle <mvallebr@gmail.com<mailto:mvallebr@gmail.com>>
Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Date: Wednesday, September 19, 2012 1:47 PM
To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Subject: Re: Correct model

2012/9/19 Hiller, Dean <Dean.Hiller@nrel.gov<mailto:Dean.Hiller@nrel.gov>>
Thinking out loud and I think a bit towards playOrm's model though you don’t' need to use
playroom for this.

1. I would probably have a User with the requests either embedded in or the Foreign keys to
the requests…either is fine as long as you get the user get ALL FK's and make one request
to get the requests for that user

This was my first option. However, everytime I have a new request I would need to read the
column "request_ids", update its value, and them write the result. This would be a read-before-write,
which is bad in Cassandra, right? Or you were talking about other kinds of FKs?

2. I would create rows for index and index each month of data OR maybe index each day of data(depends
on your system).  Then, I can just query into the index for that one month.  With playOrm
S-SQL, this is a simple PARTITIONS r(:thismonthParititonId) SELECT r FROM Request r where
r.date > :date OR you just do a column range query doing the same thing into your index.
 The index is basically the wide row pattern ;) with composite keys of <date>.<rowkey
of request>

I would consider playOrm in a later step in my project, as my understanding now is it is good
to store relational data, structured data. I cannot predict which columns I am going to store
in requestCF. But regardless, even in Cassandra, you would still use a composite key, but
it seems you would create an indexCf using the wide row pattern, and each request would have
its own id, right? But why? Wouldn't it be faster to have a composite key in the requestCF
itself?


From: Marcelo Elias Del Valle <mvallebr@gmail.com<mailto:mvallebr@gmail.com><mailto:mvallebr@gmail.com<mailto:mvallebr@gmail.com>>>
Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org><mailto:user@cassandra.apache.org<mailto:user@cassandra.apache.org>>"
<user@cassandra.apache.org<mailto:user@cassandra.apache.org><mailto:user@cassandra.apache.org<mailto:user@cassandra.apache.org>>>
Date: Wednesday, September 19, 2012 1:02 PM
To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org><mailto:user@cassandra.apache.org<mailto:user@cassandra.apache.org>>"
<user@cassandra.apache.org<mailto:user@cassandra.apache.org><mailto:user@cassandra.apache.org<mailto:user@cassandra.apache.org>>>
Subject: Correct model

I am new to Cassandra and NoSQL at all.
I built my first model and any comments would be of great help. I am describing my thoughts
bellow.

It's a very simple model. I will need to store several users and, for each user, I will need
to store several requests. It request has it's insertion time. As the query comes first, here
are the only queries I will need to run against this model:
- Select all the requests for an user
- Select all the users which has new requests, since date D

I created the following model: an UserCF, whose key is a userID generated by TimeUUID, and
a RequestCF, whose key is composite: UserUUID + timestamp. For each user, I will store basic
data and, for each request, I will insert a lot of columns.

My questions:
- Is the strategy of using a composite key good for this case? I thought in other solutions,
but this one seemed to be the best. Another solution would be have a non-composite key of
type UUID for the requests, and have another CF to relate user and request.
- To perform the second query, instead of selecting if each user has a request inserted after
date D, I thought in storing the last request insertion date into the userCF, everytime I
have a new insert for the user. It would be a data replication, but I would have no read-before-write
and I am guessing the second query would perform faster.

Any thoughts?

--
Marcelo Elias Del Valle
http://mvalle.com - @mvallebr



--
Marcelo Elias Del Valle
http://mvalle.com - @mvallebr

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