org.apache.cassandra.db

Interface ReadQuery

All Known Implementing Classes:

PartitionRangeReadCommand, ReadCommand, SinglePartitionReadCommand, SinglePartitionReadCommand.Group

public interface ReadQuery

Generic abstraction for read queries.

The main implementation of this is ReadCommand but we have this interface because SinglePartitionReadCommand.Group is also consider as a "read query" but is not a ReadCommand.

Field Summary

Fields

Modifier and Type	Field and Description
static ReadQuery	EMPTY

Method Summary

Modifier and Type	Method and Description
PartitionIterator	execute(ConsistencyLevel consistency, ClientState clientState) Executes the query at the provided consistency level.
PartitionIterator	executeInternal(ReadOrderGroup orderGroup) Execute the query for internal queries (that is, it basically executes the query locally).
QueryPager	getPager(PagingState pagingState, int protocolVersion) Returns a pager for the query.
DataLimits	limits() The limits for the query.
boolean	selectsClustering(DecoratedKey key, Clustering clustering)
boolean	selectsKey(DecoratedKey key)
ReadOrderGroup	startOrderGroup() Starts a new read operation.

Field Detail

EMPTY

static final ReadQuery EMPTY

Method Detail

startOrderGroup

ReadOrderGroup startOrderGroup()

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.

Returns:

a newly started order group for this ReadQuery.

execute

PartitionIterator execute(ConsistencyLevel consistency,
                          ClientState clientState)
                   throws RequestExecutionException

Executes the query at the provided consistency level.

Parameters:

consistency - the consistency level to achieve for the query.

clientState - the ClientState for the query. In practice, this can be null unless consistency is a serial consistency.

Returns:

the result of the query.

Throws:

RequestExecutionException

executeInternal

PartitionIterator executeInternal(ReadOrderGroup orderGroup)

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

Parameters:

orderGroup - the ReadOrderGroup protecting the read.

Returns:

the result of the query.

getPager

QueryPager getPager(PagingState pagingState,
                    int protocolVersion)

Returns a pager for the query.

Parameters:

pagingState - the PagingState to start from if this is a paging continuation. This can be null if this is the start of paging.

protocolVersion - the protocol version to use for the paging state of that pager.

Returns:

a pager for the query.

limits

DataLimits limits()

The limits for the query.

Returns:

The limits for the query.

selectsKey

boolean selectsKey(DecoratedKey key)

Returns:

true if the read query would select the given key, including checks against the row filter, if checkRowFilter is true

selectsClustering

boolean selectsClustering(DecoratedKey key,
                          Clustering clustering)

Returns:

true if the read query would select the given clustering, including checks against the row filter, if checkRowFilter is true