Venki Korukanti created DRILL-4729:
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             Summary: Add support for prepared statement implementation on 
server side
                 Key: DRILL-4729
                 URL: https://issues.apache.org/jira/browse/DRILL-4729
             Project: Apache Drill
          Issue Type: Sub-task
          Components: Metadata
            Reporter: Venki Korukanti
            Assignee: Venki Korukanti
             Fix For: 1.8.0


Currently Drill JDBC/ODBC driver implements its own prepared statement 
implementation, which basically issues limit 0 query to get the metadata and 
then executes the actual query. So the query is planned twice (for metadata 
fetch and actual execution). Proposal is to move that logic to server where we 
can make optimizations without disrupting/updating the JDBC/ODBC drivers.

*  {{PreparedStatement createPreparedStatement(String query)}}. 
{{PreparedStatement}} object contains the following:
** {{ResultSetMetadata getResultSetMetadata()}}
*** {{ResultsSetMetadata}} contains methods to fetch info about output columns 
of the query. What info these methods provide is given in this 
[spreadsheet|https://docs.google.com/spreadsheets/d/1A6nqUQo5xJaZDQlDTittpVrK7t4Kylycs3P32Yn_O5k/edit?usp=sharing].
 It lists the ODBC/JDBC requirements and what Drill will provided through 
object {{ResultsSetMetadata}}.
*** Server can put more info here which is opaque to client and use it in 
server when the client sends execute prepared statement query request. 

Overload the current submit query API to take the {{PreparedStatement}} 
returned above. 

In the initial implementation, server side implementation of 
{{createPreparedStatement}} API is implemented as follows:
* Runs the query with {{LIMIT 0}}, gets the schema
* Convert the query into a binary blob and set it as opaque object in 
{{PreparedStatement}}.

When the {{PreparedStatement}} is submitted for execution, reconstruct the 
query from binary blob in opaque component of {{PreparedStatement}} and execute 
it from scratch. 

Opaque component of the {{PreparedStatement}} is where we can save more 
information which we can use for optimizations/speedups.

NOTE: We are not going to worry about parameters in prepared query in initial 
implementation. We can provide the functionality later if there is sufficient 
demand from Drill community.



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