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 >> >>> >> >> >>> >> >> >> >> >>
