org.apache.lens.server.api.driver.hooks

Interface DriverQueryHook

All Known Implementing Classes:

ChainedDriverQueryHook, NoOpDriverQueryHook, QueryCostBasedQueryHook, UserBasedQueryHook

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 Note: Note if the hook updates any configuration, same should be reflected in QueryContext via AbstractQueryContext.updateConf(java.util.Map) to ensure the modified configuration is persisted and is available on server restarts and other bookkeeping needs.

Method Summary

Modifier and Type	Method and Description
void	postDriverSelection(AbstractQueryContext ctx) Called just after driver has been selected to execute a query.
void	postEstimate(AbstractQueryContext ctx) Called just after a successful estimate operation is tried on this driver
void	postRewrite(AbstractQueryContext ctx) Called just after a successful rewrite operation is tried on this driver
void	preEstimate(AbstractQueryContext ctx) Called just before estimate operation is tried on this driver Note : Estimate operation will be skipped if rewrite operation fails for this driver
void	preLaunch(QueryContext ctx) Called just before launching the query on the selected driver.
void	preRewrite(AbstractQueryContext ctx) Called just before rewrite operation is tried on this driver
void	setDriver(LensDriver driver) This setter method is called by the driver once hook instance is created.

Method Detail

setDriver

void setDriver(LensDriver driver)

This setter method is called by the driver once hook instance is created. This driver information can be used while extracting driver specific information form the QueryContext.

Parameters:

driver -

preRewrite

void preRewrite(AbstractQueryContext ctx)
         throws LensException

Called just before rewrite operation is tried on this driver

Parameters:

ctx -

Throws:

LensException

postRewrite

void postRewrite(AbstractQueryContext ctx)
          throws LensException

Called just after a successful rewrite operation is tried on this driver

Parameters:

ctx -

Throws:

LensException

preEstimate

void preEstimate(AbstractQueryContext ctx)
          throws LensException

Called just before estimate operation is tried on this driver Note : Estimate operation will be skipped if rewrite operation fails for this driver

Parameters:

ctx -

Throws:

LensException

postEstimate

void postEstimate(AbstractQueryContext ctx)
           throws LensException

Called just after a successful estimate operation is tried on this driver

Parameters:

ctx -

Throws:

LensException

postDriverSelection

void postDriverSelection(AbstractQueryContext ctx)
                  throws LensException

Called just after driver has been selected to execute a query.

Parameters:

ctx -

Throws:

LensException

preLaunch

void preLaunch(QueryContext ctx)
        throws LensException

Called just before launching the query on the selected driver.

Parameters:

ctx -

Throws:

LensException