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From "Peer, Oded" <Oded.P...@rsa.com>
Subject RE: Data model suggestions
Date Sun, 26 Apr 2015 08:29:20 GMT
I would maintain two tables.
An “archive” table that holds all the active and inactive records, and is updated hourly
(re-inserting the same record has some compaction overhead but on the other side deleting
records has tombstones overhead).
An “active” table which holds all the records in the last external API invocation.
To avoid tombstones and read-before-delete issues “active” should actually a synonym,
an alias, to the most recent active table.
I suggest you create two identical tables, “active1” and “active2”, and an “active_alias”
table that informs which of the two is the most recent.
Thus when you query the external API you insert the data to “archive” and to the unaliased
“activeN” table, switch the alias value in “active_alias” and truncate the new unaliased
“activeM” table.
No need to query the data before inserting it. Make sure truncating doesn’t create automatic
snapshots.


From: Narendra Sharma [mailto:narendra.sharma@gmail.com]
Sent: Friday, April 24, 2015 6:53 AM
To: user@cassandra.apache.org
Subject: Re: Data model suggestions


I think one table say record should be good. The primary key is record id. This will ensure
good distribution.
Just update the active attribute to true or false.
For range query on active vs archive records maintain 2 indexes or try secondary index.
On Apr 23, 2015 1:32 PM, "Ali Akhtar" <ali.rac200@gmail.com<mailto:ali.rac200@gmail.com>>
wrote:
Good point about the range selects. I think they can be made to work with limits, though.
Or, since the active records will never usually be > 500k, the ids may just be cached in
memory.

Most of the time, during reads, the queries will just consist of select * where primaryKey
= someValue . One row at a time.

The question is just, whether to keep all records in one table (including archived records
which wont be queried 99% of the time), or to keep active records in their own table, and
delete them when they're no longer active. Will that produce tombstone issues?

On Fri, Apr 24, 2015 at 12:56 AM, Manoj Khangaonkar <khangaonkar@gmail.com<mailto:khangaonkar@gmail.com>>
wrote:
Hi,
If your external API returns active records, that means I am guessing you need to do a select
* on the active table to figure out which records in the table are no longer active.
You might be aware that range selects based on partition key will timeout in cassandra. They
can however be made to work using the column cluster key.
To comment more, We would need to see your proposed cassandra tables and queries that you
might need to run.
regards



On Thu, Apr 23, 2015 at 9:45 AM, Ali Akhtar <ali.rac200@gmail.com<mailto:ali.rac200@gmail.com>>
wrote:
That's returned by the external API we're querying. We query them for active records, if a
previous active record isn't included in the results, that means its time to archive that
record.

On Thu, Apr 23, 2015 at 9:20 PM, Manoj Khangaonkar <khangaonkar@gmail.com<mailto:khangaonkar@gmail.com>>
wrote:
Hi,
How do you determine if the record is no longer active ? Is it a perioidic process that goes
through every record and checks when the last update happened ?
regards

On Thu, Apr 23, 2015 at 8:09 AM, Ali Akhtar <ali.rac200@gmail.com<mailto:ali.rac200@gmail.com>>
wrote:
Hey all,

We are working on moving a mysql based application to Cassandra.

The workflow in mysql is this: We have two tables: active and archive . Every hour, we pull
in data from an external API. The records which are active, are kept in 'active' table. Once
a record is no longer active, its deleted from 'active' and re-inserted into 'archive'

The purpose for that, is because most of the time, queries are only done against the active
records rather than archived. Therefore keeping the active table small may help with faster
queries, if it only has to search 200k records vs 3 million or more.

Is it advisable to keep the same data model in Cassandra? I'm concerned about tombstone issues
when records are deleted from active.

Thanks.


--
http://khangaonkar.blogspot.com/



--
http://khangaonkar.blogspot.com/

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