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From Tyler Hobbs <>
Subject Re: Consolidating records and TTL
Date Wed, 04 Jun 2014 22:37:45 GMT
Just use an atomic batch that holds both the insert and deletes:

On Tue, Jun 3, 2014 at 2:13 PM, Charlie Mason <> wrote:

> Hi All.
> I have a system thats going to make possibly several concurrent changes to
> a running total. I know I could use a counter for this. However I have
> extra meta data I can store with the changes which would allow me to reply
> the changes. If I use a counter and it looses some writes I can't recover
> it as I will only have its current total not the extra meta data to know
> where to replay from.
> What I was planning to do was write each change of the value to a CQL
> table with a Time UUID as a row level primary key as well as a partition
> key. Then when I need to read the running total back I will do a query for
> all the changes and add them up to get the total.
> As there could be tens of thousands of these I want to have a period after
> which these are consolidated. Most won't be any where near that but a few
> will which I need to be able to support. So I was also going to have a
> consolidated total table which holds the UUID of the values consolidated up
> to. Since I can bound the query for the recent updates by the UUID I should
> be able to avoid all the tombstones. So if the read encounters any changes
> that can be consolidated it inserts a new consolidated value and deletes
> the newly consolidated changes.
> What I am slightly worried about is what happens if the consolidated value
> insert fails but the deletes to the change records succeed. I would be left
> with an inconsistent total indefinitely. I have come up with a couple of
> ideas:
> 1, I could make it require all nodes to acknowledge it before deleting the
> difference records.
> 2, May be I could have another period after its consolidated but before
> its deleted?
> 3, Is there anyway I could use the TTL to allow to it to be deleted after
> a period of time? Chances are another read would come in and fix the value.
> Anyone got any other suggestions on how I could implement this?
> Thanks,
> Charlie M

Tyler Hobbs
DataStax <>

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