Hmm, what does it mean by read only? You can use it to read data from HBase?
- Henry On Mon, Mar 24, 2014 at 2:34 PM, Kasper Sørensen <[email protected]> wrote: > A quick update on this since the module has now been merged into the master > branch: > > 1) Module is still read-only. This is accepted for now (unless someone > wants to help change it of course). > > 2) Metadata mapping is still working in two modes: a) we discover the > column families and expose them as byte-array maps (not very useful, but > works as a "lowest common denominator") and b) the user provides a set of > SimpleTableDef (which now has a convenient parser btw.:)) and gets his > table mapping as he wants it. > > 3) Querying now has special support for lookup-by-id type queries where we > will use HBase Get instead of Scan. We also have good support for > LIMIT/"maxRows", but not OFFSET/"firstRow" (in those cases we will scan > past the first records on the client side). > > 4) Dependencies seems to be a pain still. HBase and Hadoop comes in many > flavours and all are not compatible. I doubt there's a lot we can do about > it, except ask the users to provide their own HBase dependency as per their > backend version. We should probably thus make all our HBase/Hadoop > dependencies <optional>true</optional> in order to not influence the > typical clients. > > Kasper > > > 2014-02-24 17:08 GMT+01:00 Kasper Sørensen <[email protected]>: > >> Hi Henry, >> >> Yea the Phoenix project is definately an interesting approach to making MM >> capable of working with HBase. The only downside to me is that it seems >> they do a lot of intrusive stuff to HBase like creating new index tables >> etc... I would normally not "allow" that for a simple connector. >> >> Maybe we should simply support both styles. And in the case of Phoenix, I >> guess we could simply go through the JDBC module of MetaModel and connect >> via their JDBC driver... Is that maybe a route, do you know? >> >> - Kasper >> >> >> 2014-02-24 6:37 GMT+01:00 Henry Saputra <[email protected]>: >> >> We could use the HBase client library from the store I suppose. >>> The issue I am actually worry is actually adding real query support >>> for column based datastore is kind of big task. >>> Apache Phoenix tried to do that so maybe we could leverage the SQL >>> planner layer to provide the implementation of the query execution to >>> HBase layer? >>> >>> - Henry >>> >>> >>> On Mon, Feb 17, 2014 at 9:33 AM, Kasper Sørensen >>> <[email protected]> wrote: >>> > Thanks for the input Henry. With your experience, do you then also >>> happen >>> > to know of a good thin client-side library? I imagine that we could >>> maybe >>> > use a REST client instead of the full client we currently use. That >>> would >>> > save us a ton of dependency-overhead I think. Or is it a non-issue in >>> your >>> > mind, since HBase users are used to this overhead? >>> > >>> > >>> > 2014-02-16 7:16 GMT+01:00 Henry Saputra <[email protected]>: >>> > >>> >> For 1 > I think adding read only to HBase should be ok because most >>> >> update to HBase either through HBase client or REST via Stargate [1] >>> >> or Thrift >>> >> >>> >> For 2 > In Apache Gora we use Avro to do type mapping to column and >>> >> generate POJO java via Avro compiler. >>> >> >>> >> For 3 > This is the one I am kinda torn. Apache Phoenix incubating try >>> >> to provide SQL to HBase [2] via extra indexing and caching. I think >>> >> this is defeat the purpose of having NoSQL databases that serve >>> >> different purpose than Relational databse. >>> >> >>> >> I am not sure Metamodel should touch NoSQL databases which more like >>> >> column types. These databases are designed for large data with access >>> >> primary via key and not query mechanism. >>> >> >>> >> Just my 2-cent >>> >> >>> >> >>> >> [1] http://wiki.apache.org/hadoop/Hbase/Stargate >>> >> [2] http://phoenix.incubator.apache.org/ >>> >> >>> >> On Fri, Jan 24, 2014 at 11:35 AM, Kasper Sørensen >>> >> <[email protected]> wrote: >>> >> > Hi everyone, >>> >> > >>> >> > I was looking at our "hbase-module" branch and as much as I like this >>> >> idea, >>> >> > I think we've been a bit too idle with the branch. Maybe we should >>> try to >>> >> > make something final e.g. for a version 4.1. >>> >> > >>> >> > So I thought to give an overview/status of the module's current >>> >> > capabilities and it's shortcomings. We should figure out if we think >>> this >>> >> > is good enough for a first version, or if we want to do some >>> improvements >>> >> > to the module before adding it to our portfolio of MetaModel modules. >>> >> > >>> >> > 1) The module only offers read-only/query access to HBase. That is >>> in my >>> >> > opinion OK for now, we have several such modules, and this is >>> something >>> >> we >>> >> > can better add later if we straighten out the remaining topics in >>> this >>> >> mail. >>> >> > >>> >> > 2) With regards to metadata mapping: HBase is different because it >>> has >>> >> both >>> >> > column families and in column families there are columns. For the >>> sake of >>> >> > our view on HBase I would describe column families simply as "a >>> logical >>> >> of >>> >> > columns". Column families are fixed within a table, but rows in a >>> table >>> >> may >>> >> > contain arbitrary numbers of columns within each column family. >>> So... You >>> >> > can instantiate the HBaseDataContext in two ways: >>> >> > >>> >> > 2a) You can let MetaModel discover the metadata. This unfortunately >>> has a >>> >> > severe limitation. We discover the table names and column families >>> using >>> >> > the HBase API. But the actual columns and their contents cannot be >>> >> provided >>> >> > by the API. So instead we simply expose the column families with a >>> MAP >>> >> data >>> >> > types. The trouble with this is that the keys and values of the maps >>> will >>> >> > simply be byte-arrays ... Usually not very useful! But it's sort of >>> the >>> >> > only thing (as far as I can see) that's "safe" in HBase, since HBase >>> >> allows >>> >> > anything (byte arrays) in it's columns. >>> >> > >>> >> > 2b) Like in e.g. MongoDb or CouchDb modules you can provide an array >>> of >>> >> > tables (SimpleTableDef). That way the user defines the metadata >>> himself >>> >> and >>> >> > the implementation assumes that it is correct (or else it will >>> break). >>> >> The >>> >> > good thing about this is that the user can define the proper data >>> types >>> >> > etc. for columns. The user defines the column family and column name >>> by >>> >> > setting defining the MetaModel column name as this: "family:name" >>> >> > (consistent with most HBase tools and API calls). >>> >> > >>> >> > 3) With regards to querying: We've implemented basic query >>> capabilities >>> >> > using the MetaModel query postprocessor. But not all queries are very >>> >> > effective... In addition to of course full table scans, we have >>> optimized >>> >> > support of of COUNT queries and of table scans with maxRows. >>> >> > >>> >> > We could rather easily add optimized support for a couple of other >>> >> typical >>> >> > queries: >>> >> > * lookup record by ID >>> >> > * paged table scans (both firstRow and maxRows) >>> >> > * queries with simple filters/where items >>> >> > >>> >> > 4) With regards to dependencies: The module right now depends on the >>> >> > artifact called "hbase-client". This dependency has a loot of >>> transient >>> >> > dependencies so the size of the module is quite extreme. As an >>> example, >>> >> it >>> >> > includes stuff like jetty, jersey, jackson and of course hadoop... >>> But I >>> >> am >>> >> > wondering if we can have a more thin client-side than that! If anyone >>> >> knows >>> >> > if e.g. we can use the REST interface easily or so, that would maybe >>> be >>> >> > better. I'm not an expert on HBase though, so please enlighten me! >>> >> > >>> >> > Kind regards, >>> >> > Kasper >>> >> >>> >> >>
