Hive as an External Data Source

[BohuTANG]

Summary

To integration with Hive, Databend has two ways:

1. Introduce a new Hive Database Engine, like github engine did:using github database engine, this way is not flexible, for example: the parameters settings and if we have many hive databases that need to be created multiple times
2. Introduce a new Hive External Stage, this will be more flexible and scalable, treating hive as a object rather than a database

We prefer the second way.

Tasks:

• Support new stage uri for hive configurations : create stage hive url='hive://....' external stage reference
• Support new hive storage(hive metastore connector), like s3 storage
• Support query from external stage
• OpenDAL supports HDFS backend HDFS backend apache/opendal#154

[zhang2014]

Add tasks: implement hive supported file formats(https://cwiki.apache.org/confluence/display/Hive/FileFormats).

[BohuTANG]

@zhang2014 ,
Will priority to supporting the parquet/json/csv format, which is already supported by databend

[FANNG1]

excited to see the process，it would be very useful to accelerate the query on exsiting hive data。
there could some work to compatible Hive SQL （syntax, datatypes，funcs，udf）

[Xuanwo]

OpenDAL added hdfs support now, visit #5215 to get the status of this feature.

[BohuTANG]

Let's bump OpenDAL 🚀

[FANNG1]

could we do simple hive query now?

[BohuTANG]

could we do simple hive query now?

Yes, there is already a simple PoC:
https://github.com/datafuselabs/databend/blob/main/tests/suites/2_stateful_hive/00_basics/00_0000_hms_basics.sql

@dantengsky knows more about it, welcome comments :)

[FANNG1]

great! @dantengsky , could you give some instruction to setup the basic env, I'd like to join your work to improve it

[dantengsky]

great! @dantengsky , could you give some instruction to setup the basic env

great :)

1. build databend with feature hive enabled, e.g.

   cargo build --bin databend-query --features hive

2. bring up the hive meta store
   there is a docker-compose yml, which used in the CI workflow, may be a simple starting point
   https://github.com/datafuselabs/databend/blob/9ce7c71c22cdc2ba89cb1f9df70d305847270d45/.github/actions/test_stateful_hive_standalone/action.yml#L42-L45

   but it may bring up too many services ... :D

3. by default, databend will attach he default catalog of HSM, to the databend's hive catalog

   config of HSM,
   https://github.com/datafuselabs/databend/blob/9ce7c71c22cdc2ba89cb1f9df70d305847270d45/query/src/config/inner.rs#L235-L242
   where the cat of HSM is attached
   https://github.com/datafuselabs/databend/blob/9ce7c71c22cdc2ba89cb1f9df70d305847270d45/query/src/catalogs/catalog_manager.rs#L68-L77

4. A simple test case

   • create a simple test table
     https://github.com/datafuselabs/databend/blob/9ce7c71c22cdc2ba89cb1f9df70d305847270d45/.github/actions/test_stateful_hive_standalone/action.yml#L57-L60

   • access the table
     https://github.com/datafuselabs/databend/blob/9ce7c71c22cdc2ba89cb1f9df70d305847270d45/tests/suites/2_stateful_hive/00_basics/00_0000_hms_basics.sql#L2-L3

5. hive table skeleton

   the read method
   https://github.com/datafuselabs/databend/blob/9ce7c71c22cdc2ba89cb1f9df70d305847270d45/query/src/catalogs/hive/hive_table.rs#L91-L103

   • from the _plan, we can get the name of catalog
   • from the _ctx, we can get the catalog (QueryContext::get_catalog)
     which will give back a instance of hive catalog

the origin PR #4947

[FANNG1]

PR #5895 add the basic ability to query simple hive table, with following limititions:

1. not support partition table, not support to read dirs in table location
2. only suport query int and string field columns
3. just parse the first rowgroup in parquet file
4. just could parse little sized parquet file, for large parquet file may use delta encoding and not supported by arrow2 now
5. not support predict pushdown

to run though the hive sql quickly, I had done some desicions:
1, use file not rowgroup as the hive partition unit
2. create a HiveParquetBLockReader not using BlockReader, for in current implement, in executor, hive should parse meta and read not just one rowgroup. but if we use rowgroup as partition unit, we could reuse BlockReader and remove HiveParquetBlockReader
3. add some hive table field (table location& partition keys) to table meta info, maybe we should create a HiveTableMetaInfo and DataBendTableMetaInfo? abstraction and design is needed.

but maybe we could optimize the above limits&problems step by step.

as I'm a newbiew to rust&databend, feel free to give your advice to the design and code implement. cc @BohuTANG @dantengsky

[BohuTANG]

The basic framework to support the hive has been completed, this issue can be closed. We can track the hive tasks in another issue.