OK to kick things off, let me provide my own input for this discussion. Please find below my thoughts on the issues and what we need to do. Your feedback is very very welcome.
2014-01-24 Kasper Sørensen <[email protected]> > 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. > No problem > 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. > I think we could maybe add a flag here to allow MetaModel to assume that column keys are of String type. That would at least make the discovered metadata more meaningful since we can expose columns and not just column families. It's still going to be tough to figure out the value types, but we could e.g. make the Column implementations mutable and allow setting ColumnType on a "live" HBaseColumn. > 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). > This is good, but requires more of the user. > 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 > I think "lookup record by ID" is a MUST, since this is a whole other class of queries in HBase (Get instead of Scan). Other optimizations would be nice too, but for the usage I have I could live without it in the first release. > 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! > This is a big problem IMO. Anyone with HBase client experience? Would be a lot better with a thin client somehow. > Kind regards, > Kasper > > >
