Hmm I suppose a wiki page would be good. I guess we have wiki pages for some of the DataContext implementations already like Salesforce [1], POJO [2] and Composite [3] ... Maybe we should even have a page for *every *DataContext implementation there is, simply for completeness and referenceability of documentation.
[1] http://wiki.apache.org/metamodel/examples/SalesforceDataContext [2] http://wiki.apache.org/metamodel/examples/PojoDataContext [3] http://wiki.apache.org/metamodel/examples/CompositeDataContext 2014-03-24 22:44 GMT+01:00 Henry Saputra <[email protected]>: > Ok +1 > > How do you propose to document this feature? As another page in the > doc svn repo? > > - Henry > > On Mon, Mar 24, 2014 at 2:42 PM, Kasper Sørensen > <[email protected]> wrote: > > Yep. Or in slightly more technical terms: It means that the > > HBaseDataContext only implements DataContext which has these two > > significant methods: > > > > * getSchemas() > > * executeQuery(...) > > > > (Plus a bunch more methods, but those two give you the general > impression: > > Explore metadata and fire queries / reads) > > But not UpdateableDataContext, which has the write operations: > > > > * executeUpdate(...) > > > > Regards, > > Kasper > > > > > > 2014-03-24 22:37 GMT+01:00 Henry Saputra <[email protected]>: > > > >> 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 > >> >>> >> > >> >>> > >> >> > >> >> > >> >
