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From Tyler Hobbs <ty...@datastax.com>
Subject Re: Row cache for writes
Date Tue, 01 Apr 2014 23:40:03 GMT
On Mon, Mar 31, 2014 at 11:37 AM, Wayne Schroeder <
wschroeder@pinsightmedia.com> wrote:

> I found a lot of documentation about the read path for key and row caches,
> but I haven't found anything in regard to the write path.  My app has the
> need to record a large quantity of very short lived temporal data that will
> expire within seconds and only have a small percentage of the rows accessed
> before they expire.  Ideally, and I have done the math, I would like the
> data to never hit disk and just stay in memory once written until it
> expires.  How might I accomplish this?
>

It's not perfect, but set a short TTL on the data and set gc_grace_seconds
to 0 for the table.  Tombstones will still be written to disk, but almost
everything will be discarded in its first compaction.  You could also lower
the min compaction threshold for size-tiered compaction to 2 to force
compactions to happen more quickly.


>  I am not concerned about data consistency at all on this so if I could
> even avoid the commit log, that would be even better.
>

You can set durable_writes = false for the keyspace.


>
> My main concern is that I don't see any evidence that writes end up in the
> cache--that it takes at least one read to get it into the cache.  I also
> realize that, assuming I don't cause SSTable writes due to sheer quantity,
> that the data would be in memory anyway.
>
> Has anyone done anything similar to this that could provide direction?
>

Writes invalidate row cache entries, so that's not what you want.


-- 
Tyler Hobbs
DataStax <http://datastax.com/>

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