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From Jack Krupansky <jack.krupan...@gmail.com>
Subject Re: Support for ad-hoc query
Date Fri, 12 Jun 2015 14:29:53 GMT
No dispute about that. But the main design requirement Cassandra strives to
meet is to be a blazing fast transactional database - here's the key, give
me the data, and here's the key, write this data. Any additional query
requirements are a distant second at best. A big part of that transactional
speed requirement is achieved by jettisoning the overhead required for ad
hoc queries.

I think it is inevitable that Cassandra will eventually address the
requirement for ad hoc queries when it finally decides what it wants to be
when it grows up (i.e., whether to just be a niche or to subsume all of
SQL), but in the meantime DSE Search/Solr, Stratio, and TupleJump Stargate,
as well as extraction and indexing in Elasticsearch, are moderately
reasonable near-term solutions.

And I agree that having to fully model eventual (and evolving!) data
requirements and emergent anomalous conditions upfront is too big a burden
for many enterprises.


-- Jack Krupansky

On Fri, Jun 12, 2015 at 10:07 AM, <SEAN_R_DURITY@homedepot.com> wrote:

>  I will note here that the limitations on ad-hoc querying (and
> aggregates) make it much more difficult to deal with data quality problems,
> QA testing, and similar efforts, especially where people are used to a more
> relational, ad-hoc model. We have often had to extract data from Cassandra
> to Hadoop for querying by hive.
>
>
>
> Example: “We found a few records with incorrect data. How many more
> records like that are out there?”
>
>
>
>
>
> Sean Durity
>
>
>
> *From:* Peter Lin [mailto:woolfel@gmail.com]
> *Sent:* Wednesday, June 10, 2015 8:17 AM
> *To:* user@cassandra.apache.org
> *Subject:* Re: Support for ad-hoc query
>
>
>
>
>
> I'll second Jack's detailed response and add that you really should do
> some discovery to figure out what kinds of queries you may need to support.
>
> It might not be possible and often that is the case, but it's worth while
> to ask the end users what kind of reports they need to run. Allowing
> arbitrary ad-hoc queries is a known anti-pattern for cassandra. If the
> system needs to query multiple cf to derive/calculate some result, using
> Cassandra alone isn't going to do it. You'll need some other system to give
> you better query capabilities like Hive.
>
> If you need data warehouse like features, look at http://www.kylin.io/ .
> They are doing some interesting things.
>
> peter
>
>
>
> On Wed, Jun 10, 2015 at 7:58 AM, Jack Krupansky <jack.krupansky@gmail.com>
> wrote:
>
> Knowing your queries in advance is a hard-core requirement for effective
> deployment of Cassandra. Ad hoc queries are a very clear anti-pattern for
> Cassandra. DSE Search does provide support for advanced, complex, and ad
> hoc queries. Stratio and TupleJump Stargate can also be used.
>
>
>
> Back to the question of what you mean by ad hoc queries:
>
>
>
> 1. Do you expect real-time results, like sub-second, or are these
> long-running queries that might take seconds, 10 seconds or more, or even
> minutes to run?
>
> 2. Will they be very rare or quite frequent - how much load do you expect
> them to place on the cluster?
>
> 3. How complex do you expect them to be - how many clauses and operators?
>
> 4. What is their net cardinality - are they selecting just a few rows or
> many rows?
>
> 5. Do they have individual query clauses that select many rows even if the
> net combination of all select clauses is not so many rows?
>
>
>
> The requirement to perform advanced, complex, and ad hoc queries using DSE
> Search or the other techniques will almost certainly require that you use
> moderately more capable hardware, especially more RAM, for each node, and
> probably more nodes as well to reduce the row count per node since ad hoc
> queries will tend to be compute-intensive based on number of rows on the
> node.
>
>
>
> Yes, it can be done. No, it is not free or cheap. And, no, it does not
> come out of the box for a non-DSE Cassandra release. And, yes, you must
> address this requirement before deployment, not after deployment.
>
>
>
>
>   -- Jack Krupansky
>
>
>
> On Wed, Jun 10, 2015 at 1:18 AM, Srinivasa T N <seenutn@gmail.com> wrote:
>
> Thanks guys for the inputs.
>
> By ad-hoc queries I mean that I don't know the queries during cf design
> time.  The data may be from single cf or multiple cf.  (This feature maybe
> required if I want to do analysis on the data stored in cassandra, do you
> have any better ideas)?
>
> Regards,
>
> Seenu.
>
>
>
> On Tue, Jun 9, 2015 at 5:57 PM, Peter Lin <woolfel@gmail.com> wrote:
>
>
>
> what do you mean by ad-hoc queries?
>
> Do you mean simple queries against a single column family aka table?
>
> Or do you mean MDX style queries that looks at multiple tables?
>
> if it's MDX style queries, many people extract data from Cassandra into a
> data warehouse that support multi-dimensional cubes. This works well when
> the extracted data is a small subset and fits neatly in a data warehouse.
>
> As others have stated, Cassandra isn't great at ad-hoc. For MDX style
> queries, Cassandra wasn't designed for it. One thing we've done for our own
> project is to combine solr with our own fuzzy index to make ad-hoc queries
> against a single table more friendly.
>
>
>
> On Tue, Jun 9, 2015 at 2:38 AM, Srinivasa T N <seenutn@gmail.com> wrote:
>
> Hi All,
>
>    I have an web application running with my backend data stored in
> cassandra.  Now I want to do some analysis on the data stored which
> requires some ad-hoc queries fired on cassandra.  How can I do the same?
>
> Regards,
>
> Seenu.
>
>
>
>
>
>
>
>
>
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