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HBase >> mail # dev >> keyvalue cache


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Re: keyvalue cache
I guess the benefit of the KV cache is that you are not holding entire 64K
blocks in memory when you only care about 200 bytes of them.  Would an
alternative be to set a small block size (2KB or less)?

The problems with small block sizes would be expensive block cache
management overhead and inefficient scanning IO due to lack of read-ahead.
 Maybe improving the cache management and read-ahead would be more general
improvements that don't add as much complexity?

I'm having a hard time envisioning how you would do invalidations on the KV
cache and how you would merge its entries into a scan, etc.  Would it
basically be a memstore in front of the memstore where KVs get individually
invalidated instead of bulk-flushed?  Would it be sorted or hashed?

Matt

On Wed, Apr 4, 2012 at 10:35 AM, Enis Söztutar <[EMAIL PROTECTED]> wrote:

> As you said, caching the entire row does not make much sense, given that
> the families are by contract the access boundaries. But caching column
> families might be a good trade of for dealing with the per-item overhead.
>
> Also agreed on cache being configurable at the table or better cf level. I
> think we can do something like enable_block_cache = true,
> enable_kv_cache=false, per column family.
>
> Enis
>
> On Tue, Apr 3, 2012 at 11:03 PM, Vladimir Rodionov
> <[EMAIL PROTECTED]>wrote:
>
> > Usually make sense for tables with random mostly access (point queries)
> > For short-long scans block cache is preferable.
> > Cassandra has it (Row cache) but as since they cache the whole row (which
> > can be very large) in many cases
> > it has sub par performance. Make sense to make caching configurable:
> table
> > can use key-value cache and do not use block cache
> > and vice verse.
> >
> > Best regards,
> > Vladimir Rodionov
> > Principal Platform Engineer
> > Carrier IQ, www.carrieriq.com
> > e-mail: [EMAIL PROTECTED]
> >
> > ________________________________________
> > From: Enis Söztutar [[EMAIL PROTECTED]]
> > Sent: Tuesday, April 03, 2012 3:34 PM
> > To: [EMAIL PROTECTED]
> > Subject: keyvalue cache
> >
> > Hi,
> >
> > Before opening the issue, I though I should ask around first. What do you
> > think about a keyvalue cache sitting on top of the block cache? It is
> > mentioned in the big table paper, and it seems that zipfian kv access
> > patterns might benefit from something like this a lot. I could not find
> > anybody who proposed that before.
> >
> > What do you guys think? Should we pursue a kv query-cache. My gut feeling
> > says that especially for some workloads we might gain significant
> > performance improvements, but we cannot verify it, until we implement and
> > profile it, right?
> >
> > Thanks,
> > Enis
> >
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