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From E S <>
Subject Re: Achieving isolation on single row modifications with batch_mutate
Date Tue, 30 Nov 2010 14:18:51 GMT
I'm chunking up a larger blob.  Basically the size of each row can vary 
(averages around 500K - 1MB), with some outliers in the 50 MB range.   However, 
when I do an update, I can usually just read/update a portion of that blob.  A 
lot of my read operations can also work on a smaller chunk.  The number of 
columns is going to depend on the size of the blob itself.  I'm also considering 
using supercolumns to have higher save granularity.

My biggest problem is that I will have to update these rows a lot (several times 
a day) and often very quickly (process 15 thousand in 2-3 minutes).  While I 
think I could probably scale up with a lot of hardware to meet that load, it 
seems like I'm doing much much more work than I need to (processing 15 GB of 
data in 2-3 minutes as opposes to 100 MB).  I also worry about handling our 
future data size needs.

I can split the blob up without a lot of extra complexity but am worried about 
how to have readers read a non-corrupted version of the object, since sometimes 
I'll have to update multiple chunks as one unit.

From: Tyler Hobbs <>
Sent: Tue, November 30, 2010 12:57:07 AM
Subject: Re: Achieving isolation on single row modifications with batch_mutate

In this case, it sounds like you should combine columns A and B if you
are writing them both at the same time, reading them both at the same
time, and need them to be consistent.

Obviously, you're probably dealing with more than two columns here, but
there's generally not any value in splitting something into multiple columns
if you're always writing and reading all of them at the same time.

Or are you talking about chunking huge blobs across a row?

- Tyler

On Sat, Nov 27, 2010 at 10:12 AM, E S <> wrote:

I'm trying to figure out the best way to achieve single row modification
>isolation for readers.
>As an example, I have 2 rows (1,2) with 2 columns (a,b).  If I modify both 
>I don't care if the user sees the write operations completed on 1 and not on 2
>for a short time period (seconds).  I also don't care if when reading row 1 the
>user gets the new value, and then on a re-read gets the old value (within a few
>seconds).  Because of this, I have been planning on using a consistency level 
>However, if I modify both columns A,B on a single row, I need both changes on
>the row to be visible/invisible atomically.  It doesn't matter if they both
>become visible and then both invisible as the data propagates across nodes, but
>a half-completed state on an initial read will basically be returning corrupt
>data given my apps consistency requirements.  My understanding from the FAQ 
>this single row multicolumn change provides no read isolation, so I will have
>this problem.  Is this correct?  If so:
>Question 1:  Is there a way to get this type of isolation without using a
>distributed locking mechanism like cages?
>Question 2:  Are there any plans to implement this type of isolation within
>Question 3:  If I went with a distributed locking mechanism, what consistency
>level would I need to use with Cassandra?  Could I still get away with a
>consistency level of one?  It seems that if the initial write is done in a
>non-isolated way, but if cross-node row synchronizations are done all or
>nothing, I could still use one.
>Question 4:  Does anyone know of a good c# alternative to cages/zookeeper?
>Thanks for any help with this!

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