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From Andy Tolbert <andrew.tolb...@datastax.com>
Subject Re: Migrating a Limit/Offset Pagination and Sorting to Cassandra
Date Wed, 04 Oct 2017 13:45:02 GMT
Hi Daniel,

To answer this question:

> How long is the paginationState from the driver current?

The paging state itself contains information about the position in data
where to proceed from, so you don't need to worry about it becoming
stale/invalid.  The only exception is if you upgrade your cluster and start
using a newer protocol version, at which point the paging state will likely
become invalid.  The java driver guide has an explanation of saving and
reusing the paging state
<http://docs.datastax.com/en/developer/java-driver/3.3/manual/paging/#saving-and-reusing-the-paging-state>
that explains this.

Thanks,
Andy

On Wed, Oct 4, 2017 at 1:36 AM Greg Saylor <gregs@net-virtual.com> wrote:

> Without knowing other details, of course, have you considered using
> something like Elassandra?  That is a pretty tightly integrated Cassandra +
> Elastic Search solution.   You’d insert data into Cassandra like you do
> normally, then query it with Elastic Search.  Of course this would increase
> the size of your storage requirements.
>
> - Greg
>
>
> On Oct 3, 2017, at 11:10 PM, Daniel Hölbling-Inzko <
> daniel.hoelbling-inzko@bitmovin.com> wrote:
>
> Thanks Kurt,
> I thought about that but one issue is that we are doing limit/offset not
> pages. So one customer can choose to page through the list in 10 Item
> increments, another might want to page through with 100 elements per page.
> So I can't have a clustering key that represents a page range.
>
> What I was thinking about doing was saving the paginationState in a
> separate table along with limit/offset info of the last query the
> paginationState originated from so I can use the last paginationState to
> continue the iteration from if the customer requests the next page with the
> same limit but a different offset.
> This breaks down if the customer does a cold offset=1000 request but
> that's something I can throw error messages for at, what I do need to
> support is a customer doing
> Request 1: offset=0 + limit=100
> Request 2: offset=100 + limit=100
> Request 3: offset=200 + limit=100
>
> So next question would be: How long is the paginationState from the driver
> current? I was thinking about inserting the paginationState with a TTL into
> another Cassandra table - not sure if that's smart though.
>
> greetings Daniel
>
> On Tue, 3 Oct 2017 at 12:20 kurt greaves <kurt@instaclustr.com> wrote:
>
>> I get the impression that you are paging through a single partition in
>> Cassandra? If so you should probably use bounds on clustering keys to get
>> your "next page". You could use LIMIT as well here but it's mostly
>> unnecessary. Probably just use the pagesize that you intend for the API.
>>
>> Yes you'll need a table for each sort order, which ties into how you
>> would use clustering keys for LIMIT/OFFSET. Essentially just do range
>> slices on the clustering keys for each table to get your "pages".
>>
>> Also I'm assuming there's a lot of data per partition if in-mem sorting
>> isn't an option, if this is true you will want to be wary of creating large
>> partitions and reading them all at once. Although this depends on your data
>> model and compaction strategy choices.
>>
>> On 3 October 2017 at 08:36, Daniel Hölbling-Inzko <
>> daniel.hoelbling-inzko@bitmovin.com> wrote:
>>
>>> Hi,
>>> I am currently working on migrating a service that so far was MySQL
>>> based to Cassandra.
>>> Everything seems to work fine so far, but a few things in the old
>>> services API Spec is posing some interesting data modeling challenges:
>>>
>>> The old service was doing Limit/Offset pagination which is obviously
>>> something Cassandra can't really do. I understand how paginationState works
>>> - but so far I haven't figured out a good way to make Limit/Offset work on
>>> top of paginationState (as I need to be 100% backwards compatible).
>>> The only ways which I could think of to make Limit/Offset work would
>>> create scalability issues down the road.
>>>
>>> The old service allowed sorting by any field. If I understood correctly
>>> that would require a table for each sort order right? (In-Mem sorting is
>>> not an option unfortunately)
>>> In doing so, how can I make the Java Datastax mapper save to another
>>> table (I really don't want to be writing a Subclass of the Entity for each
>>> Table to add the @Table annotation.
>>>
>>> greetings Daniel
>>>
>>
>>
>

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