org.apache.lens.server.api.driver

Interface DriverQueryHook

All Known Implementing Classes:

NoOpDriverQueryHook

public interface DriverQueryHook

Drivers should initialize a DriverQueryHook object in their initialization and expose it via LensDriver.getQueryHook(). Lens Server will invoke the driver hook at relevant points during query execution. By default each driver exposes a NoOpDriverQueryHook which does nothing when invoked. The only use case I see right now is to provide a hook just after driver has been selected for a query and before query is launched on the driver. One example usage for hive driver would be to add dynamic configuration or stall execution of a query by looking at the final translated query itself (based on table involved, filters involved, etc in the query). This interface is expected to evolve for some time as more needs for hook are discovered

Method Summary

Methods

Modifier and Type	Method and Description
void	postDriverSelection(AbstractQueryContext ctx) Called just after driver has been selected to execute a query.
void	preLaunch(QueryContext ctx) Called just before launching the query on the selected driver.

Method Detail

preLaunch

void preLaunch(QueryContext ctx)
               throws LensException

Called just before launching the query on the selected driver.

Parameters:

ctx -

Throws:

LensException

postDriverSelection

void postDriverSelection(AbstractQueryContext ctx)
                         throws LensException

Called just after driver has been selected to execute a query. Note: Note if this method updates any configuration, same should be reflected in QueryContext via AbstractQueryContext.updateConf(Map) to ensure the modified configration is persisted and is available on server restarts and other bookkeeping needs.

Parameters:

ctx -

Throws:

LensException