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From Bryan Holladay <holla...@longsight.com>
Subject Re: "SELECT *..." query times out on a particular table
Date Tue, 04 Aug 2015 00:43:20 GMT
Check Cassandra logs for tombstone threshold error
On Aug 3, 2015 7:32 PM, "Robert Coli" <rcoli@eventbrite.com> wrote:

> On Mon, Aug 3, 2015 at 2:48 PM, Sid Tantia <sid.tantia@baseboxsoftware.com
> > wrote:
>
>> Any select all or select count query on a particular table is timing out
>> with "Cassandra::Errors::TimeoutError: Timed out"
>>
>> A “SELECT * FROM <table> WHERE <partition key> = ‘<partition key
value>’
>> on the table works, but a “SELECT * FROM <table> LIMIT 1; does not work.
>> All other tables and queries work.
>>
>> Any ideas as to why this might be happening?
>>
>
> This specific question is getting to be a FAQ...
>
> Briefly :
>
> 1) Cassandra operates best when you supply PRIMARY KEY with your request.
> 2) The worst case scenario is therefore SELECT * FROM Table;
> 3) While SELECT * FROM Table; is trivial in a non-distributed RDBMS,
> Cassandra is ****NOT A NON-DISTRIBUTED RDBMS**** and so it is NOT TRIVIAL
> IN CASSANDRA
> 4) Cassandra is, instead, a distributed data-store in which most
> operations default to a timeout of fewer than a single digit number of
> seconds
> 5) So if SELECTing * FROM your Table is likely to take longer than that,
> what you'll get is a timeout
>
> The stock remediation for this FAQ is :
>
> a) don't use Cassandra for cases where you need to SELECT * FROM Table
> b) if you do have to use it for such a case, use a driver with internal
> pagination
>
> =Rob
>
>

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