More questions: + What are the requirements regards the lag between receipt of data and it showing in the system? One minute, ten minutes, an hour, or 24 hours? + How many column families?
St.Ack On Wed, Sep 2, 2009 at 11:37 PM, Schubert Zhang <[email protected]> wrote: > in line. > > On Thu, Sep 3, 2009 at 12:46 PM, stack <[email protected]> wrote: > > > > > How many machines can you use for this job? > > > Tens. (e.g. 10~20) > > > > > > Do you need to keep it all? Does some data expire (or can it be moved > > offline)? > > > Yes, we need remove old data which expire. > > > > > I see why you have timestamp as part of the key in your current hbase > > cluster -- i.e. tall tables -- as you have no other choice currently. > > > > It might make sense premaking the regions in the table. Look at how many > > regions were made the day before and go ahead and premake them to save > > yourself having to ride over splits (I can show you how to write a little > > script to do this). > > > > Does the time-series data arrive roughly on time -- e.g. all instruments > > emit the 4 o'clock readings at 4 o'clock or is there some flux in here? > In > > other words, do you have a write rate of thousands of updates per second, > > all carrying the same timestamp? > > > The data will arrive with a minutes delay. > Usually, we need to write/ingest tens of thousands of new rows. Many rows > with the same timestamp. > > > > > > St.Ack > > > > > > > > > > > Schubert > > > > > > On Thu, Sep 3, 2009 at 2:32 AM, Jonathan Gray <[email protected]> > wrote: > > > > > > > @Sylvain > > > > > > > > If you describe your use case, perhaps we can help you to understand > > what > > > > others are doing / have done similarly. Event logging is certainly > > > > something many of us have done. > > > > > > > > If you're wondering about how much load HBase can handle, provide > some > > > > numbers of what you expect. How much data in bytes are associated > with > > > each > > > > event, how many events per hour, and what operations do you want to > do > > on > > > > it? We could help you determine how big of a cluster you might need > > and > > > the > > > > kind of write/read throughput you might see. > > > > > > > > @Schubert > > > > > > > > You do not need to partition your tables by stamp. One possibility > is > > to > > > > put the stamp as the first part of your rowkeys, and in that way you > > will > > > > have the table sorted by time. Using Scan's start/stop keys, you can > > > > prevent doing a full table scan. > > > > > > > It would not work. Since our data comes fastly. In the method only one > > > region(server) are busy for writing. The throughput is bad for writing. > > > > > > > > > > > > > > For both of you... If you are storing massive amounts of streaming > > > log-type > > > > data, do you need full random read access to it? If you just need to > > > > process on subsets of time, that's easily partitioned by file. HBase > > > should > > > > be used if you need to *read* from it randomly, not streaming. If > you > > > have > > > > processing that HBase's inherent sorting, grouping, and indexing can > > > benefit > > > > from, then it also can make sense to use HBase in order to avoid > > > full-scans > > > > of data. > > > > > > > > > > I know it is a contradiction between random-access and batch > processing. > > > But > > > the features of HBase(sorting, distributed b-tree, merge/compaction) > are > > > very attractive. > > > > > > > > > > > > > > HBase is not the answer because of lack of HDFS append. You could > > buffer > > > > in something outside HDFS, close files after a certain size/time > (this > > > his > > > > what hbase does now, we can have data loss because of no > > > > appends as well), etc... > > > > > > > > Reads/writes of lots of streaming data to HBase will always be slower > > > than > > > > HDFS. HBase adds additional buffering, and the compaction/split > > > processes > > > > actually mean you copy the same data multiple times (probably 3-4 > times > > > avg > > > > which lines up with the 3-4x slowdown you see). > > > > > > > > > > > > And there is currently a patch in development (that works at least > > > > partially) to do direct-to-hdfs imports to HBase which would then be > > > nearly > > > > as fast as a normal HDFS writing job. > > > > > > > > Issue here: https://issues.apache.org/jira/browse/HBASE-48 > > > > > > > > > > > > JG > > > > > > > > > > > > Sylvain Hellegouarch wrote: > > > > > > > >> I must admit, I'm left as puzzled as you are. Our current use case > at > > > work > > > >> involve large amount of small event log writing. Of course HDFS was > > > quickly > > > >> out of question since it's not there yet to append to a file and > more > > > >> generally to handle large amount of small write ops. > > > >> > > > >> So we decided with HBase because we trust the Hadoop/HBase > > > infrastructure > > > >> will offer us the robustness and reliability we need. That being > said, > > > I'm > > > >> not feeling at ease in regards to the capacity of HBase to handle > the > > > >> potential load we are looking at inputing. > > > >> > > > >> In fact, it's a common treat of such systems, they've been designed > > with > > > a > > > >> certain use case in mind and sometimes I feel like their design and > > > >> implementation leak way too much on our infrastructure, leading us > > down > > > the > > > >> path of a virtual lock-in. > > > >> > > > >> Now I am not accusing anyone here, just observing that I find it > > really > > > >> hard to locate any industrial story of those systems in a similar > use > > > case > > > >> we have at hand. > > > >> > > > >> The number of nodes this or that company has doesn't quite interest > me > > > as > > > >> much as the way they are actually using HBase and Hadoop. > > > >> > > > >> RDBMS don't scale as well but they've got a long history and people > do > > > >> know how to optimise, use and manage them. It seems column-oriented > > > database > > > >> systems are still young :) > > > >> > > > >> - Sylvain > > > >> > > > >> Schubert Zhang a écrit : > > > >> > > > >>> Regardless Cassandra, I want to discuss some questions about > > > >>> HBase/Bigtable. Any advices are expected. > > > >>> > > > >>> Regards runing MapReduce to scan/analyze big data in HBase. > > > >>> > > > >>> Compared to sequentially reading data from HDFS files directly, > > > >>> scan/sequential-reading data from HBase is slower. (As my test, at > > > least > > > >>> 3:1 > > > >>> or 4:1). > > > >>> > > > >>> For the data in HBase, it is diffcult to only analyze specified > part > > of > > > >>> data. For example, it is diffcult to only analyze the recent one > day > > of > > > >>> data. In my application, I am considering partition data into > > different > > > >>> HBase tables (e.g. one day - one table), then, I can only touch one > > > table > > > >>> for analyze via MapReduce. > > > >>> In Google's Bigtable paper, in the "8.1 Google Analytics", they > also > > > >>> discribe this usage, but I don't know how. > > > >>> > > > >>> It is also slower to put flooding data into HBase table than > writing > > to > > > >>> files. (As my test, at least 3:1 or 4:1 too). So, maybe in the > > future, > > > >>> HBase > > > >>> can provide a bulk-load feature, like PNUTS? > > > >>> > > > >>> Many people suggest us to only store metadata into HBase tables, > and > > > >>> leave > > > >>> data in HDFS files, because our time-series dataset is very big. I > > > >>> understand this idea make sense for some simple application > > > requirements. > > > >>> But usually, I want different indexes to the raw data. It is > diffcult > > > to > > > >>> build such indexes if the the raw data files (which are raw or are > > > >>> reconstructed via MapReduce periodically on recent data ) are not > > > >>> totally > > > >>> sorted. .... HBase can provide us many expected features: sorted, > > > >>> distributed b-tree, compact/merge. > > > >>> > > > >>> So, it is very difficult for me to make trade-off. > > > >>> If I store data in HDFS files (may be partitioned), and > > metadata/index > > > in > > > >>> HBase. The metadata/index is very difficult to be build. > > > >>> If I rely on HBase totally, the performance of ingesting-data and > > > >>> scaning-data is not good. Is it reasonable to do MapReduce on > HBase? > > We > > > >>> know > > > >>> the goal of HBase is to provide random access over HDFS, and it is > a > > > >>> extention or adaptor over HDFS. > > > >>> > > > >>> ---- > > > >>> Many a time, I am thinking, maybe we need a data storage engine, > > which > > > >>> need > > > >>> not so strong consistency, and it can provide better writing and > > > >>> reading throughput like HDFS. Maybe, we can design another system > > like > > > a > > > >>> simpler HBase ? > > > >>> > > > >>> Schubert > > > >>> > > > >>> On Wed, Sep 2, 2009 at 8:56 AM, Andrew Purtell < > [email protected]> > > > >>> wrote: > > > >>> > > > >>> > > > >>> > > > >>>> To be precise, S3. http://status.aws.amazon.com/s3-20080720.html > > > >>>> > > > >>>> - Andy > > > >>>> > > > >>>> > > > >>>> > > > >>>> > > > >>>> ________________________________ > > > >>>> From: Andrew Purtell <[email protected]> > > > >>>> To: [email protected] > > > >>>> Sent: Tuesday, September 1, 2009 5:53:09 PM > > > >>>> Subject: Re: Cassandra vs HBase > > > >>>> > > > >>>> > > > >>>> Right... I recall an incident in AWS where a malformed gossip > packet > > > >>>> took > > > >>>> down all of Dynamo. Seems that even P2P doesn't mitigate against > > > corner > > > >>>> cases. > > > >>>> > > > >>>> > > > >>>> On Tue, Sep 1, 2009 at 3:12 PM, Jonathan Ellis <[email protected] > > > > > >>>> wrote: > > > >>>> > > > >>>> > > > >>>> > > > >>>>> The big win for Cassandra is that its p2p distribution model -- > > which > > > >>>>> drives the consistency model -- means there is no single point of > > > >>>>> failure. SPF can be mitigated by failover but it's really, > really > > > >>>>> hard to get all the corner cases right with that approach. Even > > > >>>>> Google with their 3 year head start and huge engineering > resources > > > >>>>> still has trouble with that occasionally. (See e.g. > > > >>>>> > > http://groups.google.com/group/google-appengine/msg/ba95ded980c8c179 > > > .) > > > >>>>> > > > >>>>> > > > >>>> > > > >>>> > > > >>>> > > > >>>> > > > >>> > > > >>> > > > >>> > > > >> > > > >> > > > > > >
