Class ScanQueryQueryToolChest
- java.lang.Object
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- org.apache.druid.query.QueryToolChest<ScanResultValue,ScanQuery>
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- org.apache.druid.query.scan.ScanQueryQueryToolChest
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public class ScanQueryQueryToolChest extends QueryToolChest<ScanResultValue,ScanQuery>
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Constructor Summary
Constructors Constructor Description ScanQueryQueryToolChest(ScanQueryConfig scanQueryConfig, GenericQueryMetricsFactory queryMetricsFactory)
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description com.fasterxml.jackson.core.type.TypeReference<ScanResultValue>
getResultTypeReference()
Returns a TypeReference object that is just passed through to Jackson in order to deserialize the results of this type of query.QueryMetrics<Query<?>>
makeMetrics(ScanQuery query)
Creates aQueryMetrics
object that is used to generate metrics for this specific query type.com.google.common.base.Function<ScanResultValue,ScanResultValue>
makePreComputeManipulatorFn(ScanQuery query, MetricManipulationFn fn)
Creates a Function that can take in a ResultType and return a new ResultType having applied the MetricManipulatorFn to each of the metrics.QueryRunner<ScanResultValue>
mergeResults(QueryRunner<ScanResultValue> runner)
This method wraps a QueryRunner.QueryRunner<ScanResultValue>
preMergeQueryDecoration(QueryRunner<ScanResultValue> runner)
Wraps a QueryRunner.RowSignature
resultArraySignature(ScanQuery query)
Returns aRowSignature
for the arrays returned byQueryToolChest.resultsAsArrays(QueryType, org.apache.druid.java.util.common.guava.Sequence<ResultType>)
.Sequence<Object[]>
resultsAsArrays(ScanQuery query, Sequence<ScanResultValue> resultSequence)
Converts a sequence of this query's ResultType into arrays.Optional<Sequence<FrameSignaturePair>>
resultsAsFrames(ScanQuery query, Sequence<ScanResultValue> resultSequence, MemoryAllocatorFactory memoryAllocatorFactory, boolean useNestedForUnknownTypes)
This batches the fetchedScanResultValue
s which have similar signatures and are consecutives.-
Methods inherited from class org.apache.druid.query.QueryToolChest
canPerformSubquery, createMergeFn, createResultComparator, decorateObjectMapper, filterSegments, getBaseResultType, getBySegmentResultType, getCacheStrategy, makePostComputeManipulatorFn, postMergeQueryDecoration
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Constructor Detail
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ScanQueryQueryToolChest
@Inject public ScanQueryQueryToolChest(ScanQueryConfig scanQueryConfig, GenericQueryMetricsFactory queryMetricsFactory)
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Method Detail
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mergeResults
public QueryRunner<ScanResultValue> mergeResults(QueryRunner<ScanResultValue> runner)
Description copied from class:QueryToolChest
This method wraps a QueryRunner. The input QueryRunner, by contract, will provide a series of ResultType objects in time order (ascending or descending). This method should return a new QueryRunner that merges the stream of ordered ResultType objects.A default implementation constructs a
ResultMergeQueryRunner
which creates aCombiningSequence
using the suppliedQueryRunner
withQueryToolChest.createResultComparator(Query)
andQueryToolChest.createMergeFn(Query)
} supplied by this toolchest.Generally speaking, the logic that exists in makePostComputeManipulatorFn should actually exist in this method. Additionally, if a query supports PostAggregations, this method should take steps to ensure that it computes PostAggregations a minimum number of times. This is most commonly achieved by computing the PostAgg results during merge and also rewriting the query such that it has the minimum number of PostAggs (most often zero).
- Overrides:
mergeResults
in classQueryToolChest<ScanResultValue,ScanQuery>
- Parameters:
runner
- A QueryRunner that provides a series of ResultType objects in time order (ascending or descending)- Returns:
- a QueryRunner that merges the stream of ordered ResultType objects
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makeMetrics
public QueryMetrics<Query<?>> makeMetrics(ScanQuery query)
Description copied from class:QueryToolChest
Creates aQueryMetrics
object that is used to generate metrics for this specific query type. This exists to allow for query-specific dimensions and metrics. That is, the ToolChest is expected to set some meaningful dimensions for metrics given this query type. Examples might be the topN threshold for a TopN query or the number of dimensions included for a groupBy query.QueryToolChests for query types in core (druid-processing) and public extensions (belonging to the Druid source tree) should use delegate this method to
GenericQueryMetricsFactory.makeMetrics(Query)
on an injected instance ofGenericQueryMetricsFactory
, as long as they don't need to emit custom dimensions and/or metrics.If some custom dimensions and/or metrics should be emitted for a query type, a plan described in "Making subinterfaces of QueryMetrics" section in
QueryMetrics
's class-level Javadocs should be followed.One way or another, this method should ensure that
QueryMetrics.query(Query)
is called with the given query passed on the created QueryMetrics object before returning.- Specified by:
makeMetrics
in classQueryToolChest<ScanResultValue,ScanQuery>
- Parameters:
query
- The query that is being processed- Returns:
- A QueryMetrics that can be used to make metrics for the provided query
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makePreComputeManipulatorFn
public com.google.common.base.Function<ScanResultValue,ScanResultValue> makePreComputeManipulatorFn(ScanQuery query, MetricManipulationFn fn)
Description copied from class:QueryToolChest
Creates a Function that can take in a ResultType and return a new ResultType having applied the MetricManipulatorFn to each of the metrics.This function's primary purpose is to help work around some challenges that exist around deserializing results across the wire. Specifically, different aggregators will generate different object types in a result set, if we wanted jackson to be able to deserialize these directly, we'd need to generate a response class for each query that jackson could use to deserialize things. That is not what we do. Instead, we have jackson deserialize Object instances and then use a MetricManipulatorFn to convert from those object instances to the actual object that the aggregator expects. As such, this would be more effectively named "makeObjectDeserializingFn".
It is safe and acceptable for implementations of this method to first validate that the MetricManipulationFn is
MetricManipulatorFns.DESERIALIZING_INSTANCE
and throw an exception if it is not. If such an exception is ever thrown, it is indicative of a bug in the caller which should be fixed by not calling this method with anything other than the deserializing manipulator function.There are some implementations where this was also tasked with computing PostAggregators, but this is actually not a good place to compute those as this function can be called in a number of cases when PostAggs are not really meaningful to compute. Instead, PostAggs should be computed in the mergeResults call and the mergeResults implementation should take care to ensure that PostAggs are only computed the minimum number of times necessary.
This function is called very early in the processing pipeline on the Broker.
- Specified by:
makePreComputeManipulatorFn
in classQueryToolChest<ScanResultValue,ScanQuery>
- Parameters:
query
- The Query that is currently being processedfn
- The function that should be applied to all metrics in the results- Returns:
- A function that will apply the provided fn to all metrics in the input ResultType object
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getResultTypeReference
public com.fasterxml.jackson.core.type.TypeReference<ScanResultValue> getResultTypeReference()
Description copied from class:QueryToolChest
Returns a TypeReference object that is just passed through to Jackson in order to deserialize the results of this type of query.- Specified by:
getResultTypeReference
in classQueryToolChest<ScanResultValue,ScanQuery>
- Returns:
- A TypeReference to indicate to Jackson what type of data will exist for this query
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preMergeQueryDecoration
public QueryRunner<ScanResultValue> preMergeQueryDecoration(QueryRunner<ScanResultValue> runner)
Description copied from class:QueryToolChest
Wraps a QueryRunner. The input QueryRunner is the QueryRunner as it exists *before* being passed to mergeResults().In fact, the return value of this method is always passed to mergeResults, so it is equivalent to just implement this functionality as extra decoration on the QueryRunner during mergeResults().
In the interests of potentially simplifying these interfaces, the recommendation is to actually not override this method and instead apply anything that might be needed here in the mergeResults() call.
- Overrides:
preMergeQueryDecoration
in classQueryToolChest<ScanResultValue,ScanQuery>
- Parameters:
runner
- The runner to be wrapped- Returns:
- The wrapped runner
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resultArraySignature
public RowSignature resultArraySignature(ScanQuery query)
Description copied from class:QueryToolChest
Returns aRowSignature
for the arrays returned byQueryToolChest.resultsAsArrays(QueryType, org.apache.druid.java.util.common.guava.Sequence<ResultType>)
. The returned signature will be the same length as each array returned byQueryToolChest.resultsAsArrays(QueryType, org.apache.druid.java.util.common.guava.Sequence<ResultType>)
.- Overrides:
resultArraySignature
in classQueryToolChest<ScanResultValue,ScanQuery>
- Parameters:
query
- same query passed toQueryToolChest.resultsAsArrays(QueryType, org.apache.druid.java.util.common.guava.Sequence<ResultType>)
- Returns:
- row signature
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resultsAsFrames
public Optional<Sequence<FrameSignaturePair>> resultsAsFrames(ScanQuery query, Sequence<ScanResultValue> resultSequence, MemoryAllocatorFactory memoryAllocatorFactory, boolean useNestedForUnknownTypes)
This batches the fetchedScanResultValue
s which have similar signatures and are consecutives. In best case it would return a single frame, and in the worst case, it would return as many frames as the number ofScanResultValue
passed.- Overrides:
resultsAsFrames
in classQueryToolChest<ScanResultValue,ScanQuery>
- Parameters:
query
- Query being executed by the toolchest. Used to determine the rowSignature of the FramesresultSequence
- results of the form returned byQueryToolChest.mergeResults(QueryRunner)
useNestedForUnknownTypes
- true if the unknown types in the results can be serded using complex types
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resultsAsArrays
public Sequence<Object[]> resultsAsArrays(ScanQuery query, Sequence<ScanResultValue> resultSequence)
Description copied from class:QueryToolChest
Converts a sequence of this query's ResultType into arrays. The array signature is given byQueryToolChest.resultArraySignature(QueryType)
. This functionality is useful because it allows higher-level processors to operate on the results of any query in a consistent way. This is useful for the SQL layer and for any algorithm that might operate on the results of an inner query.Not all query types support this method. They will throw
UnsupportedOperationException
, and they cannot be used by the SQL layer or by generic higher-level algorithms.Some query types return less information after translating their results into arrays, especially in situations where there is no clear way to translate fully rich results into flat arrays. For example, the scan query does not include the segmentId in its array-based results, because it could potentially conflict with a 'segmentId' field in the actual datasource being scanned.
It is possible that there will be multiple arrays returned for a single result object. For example, in the topN query, each
TopNResultValue
will generate a separate array for each of itsvalues
.By convention, the array form should include the __time column, if present, as a long (milliseconds since epoch).
- Overrides:
resultsAsArrays
in classQueryToolChest<ScanResultValue,ScanQuery>
resultSequence
- results of the form returned byQueryToolChest.mergeResults(org.apache.druid.query.QueryRunner<ResultType>)
- Returns:
- results in array form
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