org.apache.metamodel.jdbc

Class QuerySplitter

java.lang.Object

org.apache.metamodel.jdbc.QuerySplitter

public final class QuerySplitter
extends Object

The QuerySplitter class makes it possible to split up queries that are expected to yield a huge result set which may cause performance problems like OutOfMemoryError's or very long processing periods. The resulting queries will in union produce the same result, but in smaller bits (resultsets with less rows). Note that there is an initial performance-penalty associated with splitting the query since some queries will be executed in order to determine reasonable intervals to use for the resulting queries WHERE clauses.

See Also:

Query, DataContext

Field Summary

Fields

Modifier and Type	Field and Description
static long	DEFAULT_MAX_ROWS

Constructor Summary

Constructors

Constructor and Description
QuerySplitter(DataContext dc, Query q)

Method Summary

Methods

Modifier and Type	Method and Description
DataSet	executeQueries()
DataSet	executeQueries(List<Query> splitQueries)
long	getRowCount()
static boolean	isSplittable(Query q)
QuerySplitter	setMaxRows(long maxRows) Sets the desired maximum result set row count.
List<Query>	splitQuery() Splits the query into several queries that will together yield the same result set

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_MAX_ROWS

public static final long DEFAULT_MAX_ROWS

See Also:

Constant Field Values

Constructor Detail

QuerySplitter

public QuerySplitter(DataContext dc,
             Query q)

Method Detail

splitQuery

public List<Query> splitQuery()

Splits the query into several queries that will together yield the same result set

Returns:

a list of queries that can be executed to yield the same collective result as this QuerySplitter's query

isSplittable

public static boolean isSplittable(Query q)

getRowCount

public long getRowCount()

Returns:

the total number of rows expected from executing the query.

setMaxRows

public QuerySplitter setMaxRows(long maxRows)

Sets the desired maximum result set row count. Note that this size cannot be guaranteed, but will serve as an indicator for determining the split-size

Parameters:

maxRows -

executeQueries

public DataSet executeQueries()

executeQueries

public DataSet executeQueries(List<Query> splitQueries)