org.apache.cassandra.db

Class ReadCommand

java.lang.Object

org.apache.cassandra.db.ReadCommand

All Implemented Interfaces:

ReadQuery

Direct Known Subclasses:

PartitionRangeReadCommand, SinglePartitionReadCommand

public abstract class ReadCommand
extends java.lang.Object
implements ReadQuery

General interface for storage-engine read commands (common to both range and single partition commands).

This contains all the informations needed to do a local read.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	ReadCommand.Kind
protected static class	ReadCommand.SelectionDeserializer

Field Summary

Fields

Modifier and Type	Field and Description
protected java.util.Optional<IndexMetadata>	index
static IVersionedSerializer<ReadCommand>	legacyPagedRangeCommandSerializer
static IVersionedSerializer<ReadCommand>	legacyRangeSliceCommandSerializer
static IVersionedSerializer<ReadCommand>	legacyReadCommandSerializer
protected static org.slf4j.Logger	logger
static IVersionedSerializer<ReadCommand>	rangeSliceSerializer
static IVersionedSerializer<ReadCommand>	serializer

Fields inherited from interface org.apache.cassandra.db.ReadQuery

EMPTY

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ReadCommand(ReadCommand.Kind kind, boolean isDigestQuery, int digestVersion, boolean isForThrift, CFMetaData metadata, int nowInSec, ColumnFilter columnFilter, RowFilter rowFilter, DataLimits limits)

Method Summary

Modifier and Type	Method and Description
protected abstract void	appendCQLWhereClause(java.lang.StringBuilder sb)
abstract ClusteringIndexFilter	clusteringIndexFilter(DecoratedKey key) The clustering index filter this command to use for the provided key.
ColumnFilter	columnFilter() A filter on which (non-PK) columns must be returned by the query.
abstract ReadCommand	copy() Returns a copy of this command.
abstract MessageOut<ReadCommand>	createMessage(int version) Creates a message for this command.
ReadResponse	createResponse(UnfilteredPartitionIterator iterator, ColumnFilter selection)
int	digestVersion() If the query is a digest one, the requested digest version.
PartitionIterator	executeInternal(ReadOrderGroup orderGroup) Execute the query for internal queries (that is, it basically executes the query locally).
UnfilteredPartitionIterator	executeLocally(ReadOrderGroup orderGroup) Executes this command on the local host.
Index	getIndex(ColumnFamilyStore cfs)
abstract long	getTimeout() The configured timeout for this command.
long	indexSerializedSize(int version)
boolean	isDigestQuery() Whether this query is a digest one or not.
boolean	isForThrift() Whether this query is for thrift or not.
DataLimits	limits() The limits set on this query.
CFMetaData	metadata() The metadata for the table queried.
int	nowInSec() The time in seconds to use as "now" for this query.
protected abstract int	oldestUnrepairedTombstone()
protected abstract UnfilteredPartitionIterator	queryStorage(ColumnFamilyStore cfs, ReadOrderGroup orderGroup)
protected abstract void	recordLatency(TableMetrics metric, long latencyNanos)
RowFilter	rowFilter() Filters/Resrictions on CQL rows.
protected abstract long	selectionSerializedSize(int version)
protected abstract void	serializeSelection(DataOutputPlus out, int version)
ReadCommand	setDigestVersion(int digestVersion) Sets the digest version, for when digest for that command is requested.
ReadCommand	setIsDigestQuery(boolean isDigestQuery) Sets whether this command should be a digest one or not.
ReadOrderGroup	startOrderGroup() Starts a new read operation.
java.lang.String	toCQLString() Recreate the CQL string corresponding to this query.
protected UnfilteredPartitionIterator	withoutPurgeableTombstones(UnfilteredPartitionIterator iterator, ColumnFamilyStore cfs)

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.cassandra.db.ReadQuery

execute, getPager, selectsClustering, selectsKey

Field Detail

logger

protected static final org.slf4j.Logger logger

serializer

public static final IVersionedSerializer<ReadCommand> serializer

rangeSliceSerializer

public static final IVersionedSerializer<ReadCommand> rangeSliceSerializer

legacyRangeSliceCommandSerializer

public static final IVersionedSerializer<ReadCommand> legacyRangeSliceCommandSerializer

legacyPagedRangeCommandSerializer

public static final IVersionedSerializer<ReadCommand> legacyPagedRangeCommandSerializer

legacyReadCommandSerializer

public static final IVersionedSerializer<ReadCommand> legacyReadCommandSerializer

index

protected java.util.Optional<IndexMetadata> index

Constructor Detail

ReadCommand

protected ReadCommand(ReadCommand.Kind kind,
                      boolean isDigestQuery,
                      int digestVersion,
                      boolean isForThrift,
                      CFMetaData metadata,
                      int nowInSec,
                      ColumnFilter columnFilter,
                      RowFilter rowFilter,
                      DataLimits limits)

Method Detail

serializeSelection

protected abstract void serializeSelection(DataOutputPlus out,
                                           int version)
                                    throws java.io.IOException

Throws:

java.io.IOException

selectionSerializedSize

protected abstract long selectionSerializedSize(int version)

metadata

public CFMetaData metadata()

The metadata for the table queried.

Returns:

the metadata for the table queried.

nowInSec

public int nowInSec()

The time in seconds to use as "now" for this query.

We use the same time as "now" for the whole query to avoid considering different values as expired during the query, which would be buggy (would throw of counting amongst other things).

Returns:

the time (in seconds) to use as "now".

getTimeout

public abstract long getTimeout()

The configured timeout for this command.

Returns:

the configured timeout for this command.

columnFilter

public ColumnFilter columnFilter()

A filter on which (non-PK) columns must be returned by the query.

Returns:

which columns must be fetched by this query.

rowFilter

public RowFilter rowFilter()

Filters/Resrictions on CQL rows.

This contains the restrictions that are not directly handled by the ClusteringIndexFilter. More specifically, this includes any non-PK column restrictions and can include some PK columns restrictions when those can't be satisfied entirely by the clustering index filter (because not all clustering columns have been restricted for instance). If there is 2ndary indexes on the table, one of this restriction might be handled by a 2ndary index.

Returns:

the filter holding the expression that rows must satisfy.

limits

public DataLimits limits()

The limits set on this query.

Specified by:

limits in interface ReadQuery

Returns:

the limits set on this query.

isDigestQuery

public boolean isDigestQuery()

Whether this query is a digest one or not.

Returns:

Whether this query is a digest query.

digestVersion

public int digestVersion()

If the query is a digest one, the requested digest version.

Returns:

the requested digest version if the query is a digest. Otherwise, this can return anything.

setIsDigestQuery

public ReadCommand setIsDigestQuery(boolean isDigestQuery)

Sets whether this command should be a digest one or not.

Parameters:

isDigestQuery - whether the command should be set as a digest one or not.

Returns:

this read command.

setDigestVersion

public ReadCommand setDigestVersion(int digestVersion)

Sets the digest version, for when digest for that command is requested.

Note that we allow setting this independently of setting the command as a digest query as this allows us to use the command as a carrier of the digest version even if we only call setIsDigestQuery on some copy of it.

Parameters:

digestVersion - the version for the digest is this command is used for digest query..

Returns:

this read command.

isForThrift

public boolean isForThrift()

Whether this query is for thrift or not.

Returns:

whether this query is for thrift.

clusteringIndexFilter

public abstract ClusteringIndexFilter clusteringIndexFilter(DecoratedKey key)

The clustering index filter this command to use for the provided key.

Note that that method should only be called on a key actually queried by this command and in practice, this will almost always return the same filter, but for the sake of paging, the filter on the first key of a range command might be slightly different.

Parameters:

key - a partition key queried by this command.

Returns:

the ClusteringIndexFilter to use for the partition of key key.

copy

public abstract ReadCommand copy()

Returns a copy of this command.

Returns:

a copy of this command.

queryStorage

protected abstract UnfilteredPartitionIterator queryStorage(ColumnFamilyStore cfs,
                                                            ReadOrderGroup orderGroup)

oldestUnrepairedTombstone

protected abstract int oldestUnrepairedTombstone()

createResponse

public ReadResponse createResponse(UnfilteredPartitionIterator iterator,
                                   ColumnFilter selection)

indexSerializedSize

public long indexSerializedSize(int version)

getIndex

public Index getIndex(ColumnFamilyStore cfs)

executeLocally

public UnfilteredPartitionIterator executeLocally(ReadOrderGroup orderGroup)

Executes this command on the local host.

Parameters:

orderGroup - the operation group spanning this command

Returns:

an iterator over the result of executing this command locally.

recordLatency

protected abstract void recordLatency(TableMetrics metric,
                                      long latencyNanos)

executeInternal

public PartitionIterator executeInternal(ReadOrderGroup orderGroup)

Description copied from interface: ReadQuery

Execute the query for internal queries (that is, it basically executes the query locally).

Specified by:

executeInternal in interface ReadQuery

Parameters:

orderGroup - the ReadOrderGroup protecting the read.

Returns:

the result of the query.

startOrderGroup

public ReadOrderGroup startOrderGroup()

Description copied from interface: ReadQuery

Starts a new read operation.

This must be called before executeInternal and passed to it to protect the read. The returned object must be closed on all path and it is thus strongly advised to use it in a try-with-ressource construction.

Specified by:

startOrderGroup in interface ReadQuery

Returns:

a newly started order group for this ReadQuery.

createMessage

public abstract MessageOut<ReadCommand> createMessage(int version)

Creates a message for this command.

appendCQLWhereClause

protected abstract void appendCQLWhereClause(java.lang.StringBuilder sb)

withoutPurgeableTombstones

protected UnfilteredPartitionIterator withoutPurgeableTombstones(UnfilteredPartitionIterator iterator,
                                                                 ColumnFamilyStore cfs)

toCQLString

public java.lang.String toCQLString()

Recreate the CQL string corresponding to this query.

Note that in general the returned string will not be exactly the original user string, first because there isn't always a single syntax for a given query, but also because we don't have all the information needed (we know the non-PK columns queried but not the PK ones as internally we query them all). So this shouldn't be relied too strongly, but this should be good enough for debugging purpose which is what this is for.