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From aaron morton <aa...@thelastpickle.com>
Subject Re: single row key continues to grow, should I be concerned?
Date Tue, 20 Mar 2012 17:37:42 GMT
> The reads are only fetching slices of 20 to 100 columns max at a time from the row but
if the key is planted on one node in the cluster I am concerned about that node getting the
brunt of traffic.
What RF are you using, how many nodes are in the cluster, what CL do you read at ?

If you have lots of nodes that are in different racks the NetworkTopologyStrategy will do
a better job of distributing read load than the SimpleStrategy. The DynamicSnitch can also
result distribute load, see cassandra yaml for it's configuration. 

> I thought about breaking the column data into multiple different row keys to help distribute
throughout the cluster but its so darn handy having all the columns in one key!!
If you have a row that will continually grow it is a good idea to partition it in some way.
Large rows can slow things like compaction and repair down. If you have something above 60MB
it's starting to slow things down. Can you partition by a date range such as month ?

Large rows are also a little slower to query from
http://thelastpickle.com/2011/07/04/Cassandra-Query-Plans/

If most reads are only pulling 20 to 100 columns at a time are there two workloads ? Is it
possible store just these columns in a separate row ? If you understand how big a row may
get may be able to use the row cache to improve performance.  

Cheers


-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com

On 20/03/2012, at 2:05 PM, Blake Starkenburg wrote:

> I have a row key which is now up to 125,000 columns (and anticipated to grow), I know
this is a far-cry from the 2-billion columns a single row key can store in Cassandra but my
concern is the amount of reads that this specific row key may get compared to other row keys.
This particular row key houses column data associated with one of the more popular areas of
the site. The reads are only fetching slices of 20 to 100 columns max at a time from the row
but if the key is planted on one node in the cluster I am concerned about that node getting
the brunt of traffic.
> 
> I thought about breaking the column data into multiple different row keys to help distribute
throughout the cluster but its so darn handy having all the columns in one key!!
> 
> key_cache is enabled but row cache is disabled on the column family.
> 
> Should I be concerned going forward? Any particular advice on large wide rows?
> 
> Thanks!


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