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HBase, mail # dev - keyvalue cache


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Re: keyvalue cache
Matt Corgan 2012-04-06, 23:27
random afterthought: a delete-row command could cause problems for a simple
HashSet style cache, so you would need a sorted implementation or a more
elaborate nested structure.
On Wed, Apr 4, 2012 at 3:55 PM, Enis Söztutar <[EMAIL PROTECTED]> wrote:

> I think you are right that if you replicate the row MVCC semantics in the
> cache, then
> you can get a consistent view. I was referring to a more client side
> approach.
>
> I guess the take aways are:
>  - forget about scans, and shoot for point gets, which I agree
>  - per-kv cache overhead might be huge, but still worth trying it out.
>  - can also be architected on top of coprocessors
>  - might be complex to implement, but still some use cases would benefit a
> lot.
>  - row cache / family cache / kv cache
>
> Thanks for all the input!
>
> Enis
>
> On Wed, Apr 4, 2012 at 3:28 PM, Matt Corgan <[EMAIL PROTECTED]> wrote:
>
> > A client-side memcached setup can stay pretty consistent if you send all
> of
> > your puts and deletes through it before sending them to hbase, but yeah,
> I
> > guess you lose strict consistency under heavy read/write from multiple
> > simultaneous clients.  But, like Andy is saying, if you route the
> requests
> > through the regionserver and it talks to memcached/hazelcast, couldn't
> that
> > be fully consistent?
> >
> >
> > On Wed, Apr 4, 2012 at 3:09 PM, Andrew Purtell <[EMAIL PROTECTED]>
> > wrote:
> >
> > > I thought about trying this out once with a coprocessor, hooking the
> > Gets,
> > > with an embedded Hazelcast. That would just be a proof of concept. The
> > idea
> > > is to scale the KV cache independent of regionserver limits (maybe
> we're
> > > only giving 1 GB per RS to the value cache and a 10 GB region is hot)
> and
> > > the next step could be modifying the client to spread read load over
> > > replicas (HBASE-2357). This doesn't consider scans either.
> > >
> > >
> > > Best regards,
> > >
> > >     - Andy
> > >
> > >
> > > Problems worthy of attack prove their worth by hitting back. - Piet
> Hein
> > > (via Tom White)
> > >
> > >
> > >
> > > >________________________________
> > > > From: Matt Corgan <[EMAIL PROTECTED]>
> > > >To: [EMAIL PROTECTED]
> > > >Sent: Wednesday, April 4, 2012 2:46 PM
> > > >Subject: Re: keyvalue cache
> > > >
> > > >It could act like a HashSet of KeyValues keyed on the
> > > >rowKey+family+qualifier but not including the timestamp.  As writes
> come
> > > in
> > > >it would evict or overwrite previous versions (read-through vs
> > > >write-through).  It would only service point queries where the
> > > >row+fam+qualifier are specified, returning the latest version.
>  Wouldn't
> > > be
> > > >able to do a typical rowKey-only Get (scan behind the scenes) because
> it
> > > >wouldn't know if it contained all the cells in the row, but if you
> could
> > > >specify all your row's qualifiers up-front it could work.
> > > >
> > > >
> > > >On Wed, Apr 4, 2012 at 2:30 PM, Vladimir Rodionov
> > > ><[EMAIL PROTECTED]>wrote:
> > > >
> > > >> 1. 2KB can be too large for some applications. For example, some of
> > our
> > > >> k-v sizes < 100 bytes combined.
> > > >> 2. These tables (from 1.) do not benefit from block cache at all (we
> > did
> > > >> not try 100 B block size yet :)
> > > >> 3. And Matt is absolutely right: small block size is expensive
> > > >>
> > > >> How about doing point queries on K-V cache and  bypass K-V cache on
> > all
> > > >> Scans (when someone really need this)?
> > > >> Implement K-V cache as a coprocessor application?
> > > >>
> > > >> Invalidation of K-V entry is not necessary if all upserts operations
> > go
> > > >> through K-V cache firstly if it sits in front of MemStore.
> > > >> There will be no "stale or invalid" data situation in this case.
> > > Correct?
> > > >> No need for data to be sorted and no need for data to be merged
> > > >> into a scan (we do not use K-V cache for Scans)
> > > >>
> > > >>
> > > >> Best regards,
> > > >> Vladimir Rodionov
> > > >> Principal Platform Engineer