The scan can be an option if the cost of scanning undesired cells and discarding them trough filters is better than accessing those keys individually. I would say that as the number of 'undesired' cells decreases the scan overall performance/efficiency gets increased. It all depends on how the keys are designed to be grouped together.
2013/7/30 Ted Yu <[email protected]> > Please also go over http://hbase.apache.org/book.html#perf.reading > > Cheers > > On Tue, Jul 30, 2013 at 3:40 PM, Dhaval Shah <[email protected] > >wrote: > > > If all your keys are grouped together, why don't you use a scan with > > start/end key specified? A sequential scan can theoretically be faster > than > > MultiGet lookups (assuming your grouping is tight, you can also use > filters > > with the scan to give better performance) > > > > How much memory do you have for your region servers? Have you enabled > > block caching? Is your CPU spiking on your region servers? > > > > If you are saturating the resources on your *hot* region server then yes > > having more region servers will help. If no, then something else is the > > bottleneck and you probably need to dig further > > > > > > > > > > Regards, > > Dhaval > > > > > > ________________________________ > > From: Demian Berjman <[email protected]> > > To: [email protected] > > Sent: Tuesday, 30 July 2013 4:37 PM > > Subject: help on key design > > > > > > Hi, > > > > I would like to explain our use case of HBase, the row key design and the > > problems we are having so anyone can give us a help: > > > > The first thing we noticed is that our data set is too small compared to > > other cases we read in the list and forums. We have a table containing 20 > > million keys splitted automatically by HBase in 4 regions and balanced > in 3 > > region servers. We have designed our key to keep together the set of keys > > requested by our app. That is, when we request a set of keys we expect > them > > to be grouped together to improve data locality and block cache > efficiency. > > > > The second thing we noticed, compared to other cases, is that we > retrieve a > > bunch keys per request (500 aprox). Thus, during our peaks (3k requests > per > > minute), we have a lot of requests going to a particular region servers > and > > asking a lot of keys. That results in poor response times (in the order > of > > seconds). Currently we are using multi gets. > > > > We think an improvement would be to spread the keys (introducing a > > randomized component on it) in more region servers, so each rs will have > to > > handle less keys and probably less requests. Doing that way the multi > gets > > will be spread over the region servers. > > > > Our questions: > > > > 1. Is it correct this design of asking so many keys on each request? (if > > you need high performance) > > 2. What about splitting in more region servers? It's a good idea? How we > > could accomplish this? We thought in apply some hashing... > > > > Thanks in advance! > > >
