org.apache.druid.query.context

Class ResponseContext

java.lang.Object

org.apache.druid.query.context.ResponseContext

Direct Known Subclasses:

ConcurrentResponseContext, DefaultResponseContext

public abstract class ResponseContext
extends Object

The context for storing and passing data between chains of QueryRunners. The context is also transferred between Druid nodes with all the data it contains.

The response context consists of a set of key/value pairs. Keys are those defined in the Keys registry. Keys are indexed by key instance, not by name. The key defines the type of the associated value, including logic to merge values and to deserialize JSON values for that key.

Structure

The context has evolved to perform multiple tasks. First, it holds two kinds of information:

• Information to be returned in the query response header. These are values tagged as being in the header.
• Values passed within a single server. These are tagged with not being in the header.

Second, it performs multiple tasks:

• Registers the keys to be used in the header. But, since it also holds internal information, the internal information also needs keys, though the corresponding values are never serialized.
• Gathers information for the query as a whole.
• Merges information back up the query tree: from multiple segments, from multiple servers, etc.
• Manages headers size by dropping fields when the header would get too large.

A result is that the information the context, when inspected by a calling query, may be incomplete if some of it was previously dropped by the called query.

API

The query profile needs to obtain the full, untruncated information. To do this it piggy-backs on the set operations to obtain the full value. To ensure this is possible, code that works with standard values should call the set (or add) functions provided which will do the needed map update.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ResponseContext.AbstractKey Abstract key class which provides most functionality except the type-specific merge logic.
static class	ResponseContext.BooleanKey Boolean valued attribute with the semantics that once the flag is set true, it stays true.
static class	ResponseContext.CounterKey Long valued attribute that holds the accumulation of values assigned.
static interface	ResponseContext.Key The base interface of a response context key.
static class	ResponseContext.Keys Global registry of response context keys.
static class	ResponseContext.LongKey Long valued attribute that holds the latest value assigned.
static class	ResponseContext.SerializationResult Serialization result of ResponseContext.
static class	ResponseContext.StringKey String valued attribute that holds the latest value assigned.

Constructor Summary

Constructors

Constructor and Description
ResponseContext()

Method Summary

Modifier and Type	Method and Description
Object	add(ResponseContext.Key key, Object value) Adds (merges) a new value associated with a key to an old value.
void	addCpuNanos(long ns)
void	addMissingSegments(List<SegmentDescriptor> descriptors)
void	addRemainingResponse(String id, int count)
void	addRowScanCount(long count)
static ResponseContext	createEmpty() Create an empty DefaultResponseContext instance
static ResponseContext	deserialize(String responseContext, com.fasterxml.jackson.databind.ObjectMapper objectMapper) Deserializes a string into ResponseContext using given ObjectMapper.
Object	get(ResponseContext.Key key)
Long	getCpuNanos()
protected abstract Map<ResponseContext.Key,Object>	getDelegate()
String	getEntityTag()
List<SegmentDescriptor>	getMissingSegments()
ConcurrentHashMap<String,Integer>	getRemainingResponses()
Long	getRowScanCount()
Long	getTimeoutTime()
AtomicLong	getTotalBytes()
List<org.joda.time.Interval>	getUncoveredIntervals()
void	initialize() Initialize fields for a query context.
void	initializeMissingSegments()
void	initializeRemainingResponses()
void	initializeRowScanCount()
void	merge(ResponseContext responseContext) Merges a response context into the current.
Object	put(ResponseContext.Key key, Object value) Associates the specified object with the specified extension key.
void	putEntityTag(String eTag)
void	putQueryFailDeadlineMs(long deadlineMs)
void	putTimeoutTime(long time)
void	putUncoveredIntervals(List<org.joda.time.Interval> intervals, boolean overflowed)
Object	remove(ResponseContext.Key key)
ResponseContext.SerializationResult	serializeWith(com.fasterxml.jackson.databind.ObjectMapper objectMapper, int maxCharsNumber) Serializes the context given that the resulting string length is less than the provided limit.
Map<String,Object>	toMap()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ResponseContext

public ResponseContext()

Method Detail

getDelegate

protected abstract Map<ResponseContext.Key,Object> getDelegate()

toMap

public Map<String,Object> toMap()

createEmpty

public static ResponseContext createEmpty()

Create an empty DefaultResponseContext instance

Returns:

empty DefaultResponseContext instance

initialize

public void initialize()

Initialize fields for a query context. Not needed when merging.

initializeRemainingResponses

public void initializeRemainingResponses()

initializeMissingSegments

public void initializeMissingSegments()

initializeRowScanCount

public void initializeRowScanCount()

deserialize

public static ResponseContext deserialize(String responseContext,
                                          com.fasterxml.jackson.databind.ObjectMapper objectMapper)
                                   throws IOException

Deserializes a string into ResponseContext using given ObjectMapper.

Throws:

IllegalStateException - if one of the deserialized map keys has not been registered.

IOException

put

public Object put(ResponseContext.Key key,
                  Object value)

Associates the specified object with the specified extension key.

Throws:

IllegalStateException - if the key has not been registered.

putUncoveredIntervals

public void putUncoveredIntervals(List<org.joda.time.Interval> intervals,
                                  boolean overflowed)

putEntityTag

public void putEntityTag(String eTag)

putTimeoutTime

public void putTimeoutTime(long time)

putQueryFailDeadlineMs

public void putQueryFailDeadlineMs(long deadlineMs)

get

public Object get(ResponseContext.Key key)

getRemainingResponses

public ConcurrentHashMap<String,Integer> getRemainingResponses()

getUncoveredIntervals

public List<org.joda.time.Interval> getUncoveredIntervals()

getMissingSegments

public List<SegmentDescriptor> getMissingSegments()

getEntityTag

public String getEntityTag()

getTotalBytes

public AtomicLong getTotalBytes()

getTimeoutTime

public Long getTimeoutTime()

getRowScanCount

public Long getRowScanCount()

getCpuNanos

public Long getCpuNanos()

remove

public Object remove(ResponseContext.Key key)

add

public Object add(ResponseContext.Key key,
                  Object value)

Adds (merges) a new value associated with a key to an old value. See merge function of a context key for a specific implementation.

Throws:

IllegalStateException - if the key has not been registered.

addRemainingResponse

public void addRemainingResponse(String id,
                                 int count)

addMissingSegments

public void addMissingSegments(List<SegmentDescriptor> descriptors)

addRowScanCount

public void addRowScanCount(long count)

addCpuNanos

public void addCpuNanos(long ns)

merge

public void merge(ResponseContext responseContext)

Merges a response context into the current.

Throws:

IllegalStateException - If a key of the responseContext has not been registered.

serializeWith

public ResponseContext.SerializationResult serializeWith(com.fasterxml.jackson.databind.ObjectMapper objectMapper,
                                                         int maxCharsNumber)
                                                  throws com.fasterxml.jackson.core.JsonProcessingException

Serializes the context given that the resulting string length is less than the provided limit. This method removes some elements from context collections if it's needed to satisfy the limit. There is no explicit priorities of keys which values are being truncated. Any kind of key can be removed, the key's @{code canDrop()} attribute indicates which can be dropped. (The unit tests use a string key.) Thus keys as equally prioritized and starts removing elements from the array which serialized value length is the biggest. The resulting string will be correctly deserialized to ResponseContext.

Throws:

com.fasterxml.jackson.core.JsonProcessingException