Package oracle.nosql.driver.ops

Class QueryRequest

java.lang.Object
oracle.nosql.driver.ops.Request
oracle.nosql.driver.ops.DurableRequest
oracle.nosql.driver.ops.QueryRequest
All Implemented Interfaces:
AutoCloseable
public class QueryRequest extends DurableRequest implements AutoCloseable
A request that represents a query. A query may be specified as either a textual SQL statement (a String) or a prepared query (an instance of PreparedStatement), which may include bind variables.

For performance reasons prepared queries are preferred for queries that may be reused. This is because prepared queries bypass query compilation. They also allow for parameterized queries using bind variables.

There are two ways to get the results of a query: using an iterator or loop through partial results.

Iterator

Use NoSQLHandle.queryIterable(QueryRequest) to get an iterable that contains all the results. Usage example: 

    NoSQLHandle handle = ...;

    try (
        QueryRequest qreq = new QueryRequest().setStatement("select * from foo");
        QueryIterableResult qir = handle.queryIterable(qreq)) {
        for( MapValue row : qir) {
            // do something with row
        }
    }

Partial results

To compute and retrieve the full result set of a query, the same QueryRequest instance will, in general, have to be executed multiple times (via NoSQLHandle.query(oracle.nosql.driver.ops.QueryRequest). Each execution returns a QueryResult, which contains a subset of the result set. The following code snippet illustrates a typical query execution: 

 NoSQLHandle handle = ...;

 QueryRequest qreq = new QueryRequest().setStatement("select * from foo");

 do {
   QueryResult qres = handle.query(qreq);
   List<MapValue> results = qres.getResults();
   // do something with the results
 } while (!qreq.isDone())
Notice that a batch of results returned by a QueryRequest execution may be empty. This is because during each execution the query is allowed to read or write a maximum number of bytes. If this maximum is reached, execution stops. This can happen before any result was generated (for example, if none of the rows read satisfied the query conditions).

If an application wishes to terminate query execution before retrieving all the query results, it should call close() in order to release any local resources held by the query. This also allows the application to reuse the QueryRequest instance to run the same query from the beginning or a different query.

Parallel queries

By default a query request operates over all of the rows in a table. Large scale analytics, such as Apache Spark, Apache Hadoop, and others benefit from the ability to split a query into multiple workloads, where each workload operates on a distinct subset of a table's rows. This feature is called "parallel query" and is enabled in this driver as of release 5.4.18. The feature also requires a server that supports the feature. A server that does not support the feature will always return 0 for the maximum amount of parallelism mentioned below.

Parallel query allows an application to create a group of participating queries that operate in their own threads, processes, or machines. Each participant query declares itself to be N of M cooperating queries, where N is the individual operation and M is the total number of cooperating queries. The maximum value for M is returned in the PreparedStatement returned in a PrepareResult. This feature works best for queries that operate over the entire set of data or a simple subset constrained by a predicate. Parallel queries cannot be performed on aggregations and sorted queries. Sample code to use this feature looks like this 

 NoSQLHandle handle = ...;
 PreparedStatement ps = handle.prepare(new PrepareRequest().setStatement(
     "select * from foo")).getPreparedStatement();
 int maxParallelism = ps.getMaximumParallelism();

 // at this point up to maxParallelism queries can be operated independently,
 // each one operating on a subset of data. The total number of cooperating
 // queries can be up to maxParallelism, but smaller numbers are fine. The
 // system decides how to partition the queries across unique rows

 // Consider a maxParallism of 100 and 10 cooperating threads or processes
 // are desired. This is an example of what number 3 out of 10 would do to
 // execute a cooperating query

 QueryRequest qreq = new QueryRequest().setPreparedStatement(ps).
   setNumberOfOperations(10)  // total number of ops cooperating
   setOperationNumber(3)      // this is number 3 of 10
The query would then be executed as normal but instead of operating over the entire table the query will operate only on approximately 1/10 of the data. It is up to the application to aggregate and process results from cooperating queries. If they are to be run in separate threads or processes it is up to the application to create those runtime entities as well.

QueryRequest instances are not thread-safe. That is, if two or more application threads need to run the same query concurrently, they must create and use their own QueryRequest instances.

See Also:

  • Constructor Details

    • QueryRequest

      public QueryRequest()
      Default constructor for QueryRequest

  • Method Details

    • setCompartment

      public QueryRequest setCompartment(String compartment)
      Cloud service only.

      Sets the name or id of a compartment to be used for this operation.

      The compartment may be specified as either a name (or path for nested compartments) or as an id (OCID). A name (vs id) can only be used when authenticated using a specific user identity. It is not available if authenticated as an Instance Principal which can be done when calling the service from a compute instance in the Oracle Cloud Infrastructure. See SignatureProvider.createWithInstancePrincipal()

      Parameters:
      compartment - the name or id. If using a nested compartment, specify the full compartment path compartmentA.compartmentB, but exclude the name of the root compartment (tenant).
      Returns:
      this

    • getLimit

      public int getLimit()
      Returns the limit on number of items returned by the operation. If not set by the application this value will be 0 which means no limit set. For update query with on-premise service, returns the update limit on the number of records that can be updated in single update query. If not set by the application this value will be 0 which means no application limit set.
      Returns:
      the limit, or 0 if not set

    • setLimit

      public QueryRequest setLimit(int limit)
      Sets the limit on number of items returned by the operation. This allows an operation to return less than the default amount of data. For update query, if with on-premise service, this is to set the update limit on the number of records that can be updated in single query, if not set by the application, default service limit is used. If with cloud service, this update limit will be ignored, the maximum of records that can be updated is limited by other cloud limits maxWriteKB and maxReadKB.
      Parameters:
      limit - the limit in terms of number of items returned, or the maximum of records that can be updated in a update query.
      Returns:
      this
      Throws:
      IllegalArgumentException - if the limit value is less than 0.

    • getMaxReadKB

      public int getMaxReadKB()
      Returns the limit on the total data read during this operation, in KB. If not set by the application this value will be 0 which means no application-defined limit.
      Returns:
      the limit, or 0 if not set

    • setMaxReadKB

      public QueryRequest setMaxReadKB(int maxReadKB)
      Sets the limit on the total data read during this operation, in KB. This value can only reduce the system defined limit. This limit is independent of read units consumed by the operation. It is recommended that for tables with relatively low provisioned read throughput that this limit be reduced to less than or equal to one half of the provisioned throughput in order to avoid or reduce throttling exceptions.
      Parameters:
      maxReadKB - the limit in terms of number of KB read during this operation.
      Returns:
      this
      Throws:
      IllegalArgumentException - if the maxReadKB value is less than 0

    • getMaxWriteKB

      public int getMaxWriteKB()
      Returns the limit on the total data written during this operation, in KB. If not set by the application this value will be 0 which means no application-defined limit.
      Returns:
      the limit, or 0 if not set

    • setMaxWriteKB

      public QueryRequest setMaxWriteKB(int maxWriteKB)
      Sets the limit on the total data written during this operation, in KB. This limit is independent of write units consumed by the operation.
      Parameters:
      maxWriteKB - the limit in terms of number of KB written during this operation.
      Returns:
      this
      Throws:
      IllegalArgumentException - if the maxWriteKB value is less than 0

    • setMaxMemoryConsumption

      public QueryRequest setMaxMemoryConsumption(long maxBytes)
      Sets the maximum number of memory bytes that may be consumed by the statement at the driver for operations such as duplicate elimination (which may be required due to the use of an index on an array or map) and sorting. Such operations may consume a lot of memory as they need to cache the full result set or a large subset of it at the client memory. If the maximum amount of memory is exceeded, a exception will be throw.

      The default value is 1GB.

      Parameters:
      maxBytes - the amount of memory to use, in bytes
      Returns:
      this

    • getMaxMemoryConsumption

      public long getMaxMemoryConsumption()
      Returns the maximum number of memory bytes that may be consumed by the statement at the driver for operations such as duplicate elimination (which may be required due to the use of an index on an array or map) and sorting (sorting by distance when a query contains a geo_near() function). Such operations may consume a lot of memory as they need to cache the full result set at the client memory.

      The default value is 1GB.

      Returns:
      the maximum number of memory bytes

    • getMathContext

      public MathContext getMathContext()
      Returns the MathContext used for BigDecimal operations. MathContext.DECIMAL32 is used by default.
      Returns:
      the MathContext to use for the query

    • setMathContext

      public QueryRequest setMathContext(MathContext mathContext)
      Sets the MathContext used for BigDecimal operations. MathContext.DECIMAL32 is used by default.
      Parameters:
      mathContext - the MathContext to use for the query
      Returns:
      this

    • getStatement

      public String getStatement()
      Returns the query statement
      Returns:
      the statement, or null if it has not been set

    • setStatement

      public QueryRequest setStatement(String statement)
      Sets the query statement.
      Parameters:
      statement - the query statement
      Returns:
      this

    • getPreparedStatement

      public PreparedStatement getPreparedStatement()
      Returns the prepared query statement
      Returns:
      the statement, or null if it has not been set

    • setPreparedStatement

      public QueryRequest setPreparedStatement(PreparedStatement preparedStatement)
      Sets the prepared query statement.
      Parameters:
      preparedStatement - the prepared query statement
      Returns:
      this

    • setPreparedStatement

      public QueryRequest setPreparedStatement(PrepareResult prepareResult)
      A convenience method to set the prepared query statement from a PrepareResult
      Parameters:
      prepareResult - the result of a prepare request
      Returns:
      this

    • getContinuationKey

      @Deprecated public byte[] getContinuationKey()
      Deprecated.
      Returns the continuation key if set
      Returns:
      the key

    • setContinuationKey

      @Deprecated public QueryRequest setContinuationKey(byte[] continuationKey)
      Deprecated.
      There is no reason to use this method anymore, because setting the continuation key is now done internally.
      Sets the continuation key. This is used to continue an operation that returned this key in its QueryResult.
      Parameters:
      continuationKey - the key which should have been obtained from QueryResult.getContinuationKey()
      Returns:
      this;

    • isDone

      public boolean isDone()
      Returns true if the query execution is finished, i.e., there are no more query results to be generated. Otherwise false.
      Returns:
      whether the query is execution is finished or not

    • close

      public void close()
      Terminates the query execution and releases any memory consumed by the query at the driver. An application should use this method if it wishes to terminate query execution before retrieving all of the query results.
      Specified by:
      close in interface AutoCloseable

    • setConsistency

      public QueryRequest setConsistency(Consistency consistency)
      Sets the Consistency to use for the operation
      Parameters:
      consistency - the Consistency
      Returns:
      this

    • setDurability

      public QueryRequest setDurability(Durability durability)
      Sets the durability to use for the operation. On-premises only. This setting only applies if the query modifies a row using an INSERT, UPSERT, or DELETE statement. If the query is read-only it is ignored.
      Parameters:
      durability - the durability value. Set to null for the default durability setting on the server.
      Returns:
      this
      Since:
      5.4.0

    • getConsistency

      public Consistency getConsistency()
      Returns the consistency set for this request, or null if not set.
      Returns:
      the consistency

    • setRowMetadata

      public QueryRequest setRowMetadata(String rowMetadata)
      This method is **EXPERIMENTAL** and its behavior, signature, or even its existence may change without prior notice in future versions. Use with caution.

      Sets the row metadata to use for the operation. This setting is optional and only applies if the query modifies or deletes any rows using an INSERT, UPDATE, UPSERT or DELETE statement. If the query is read-only this setting is ignored. This is an optional parameter.

      Row metadata is associated to a certain version of a row. Any subsequent write operation will use its own row metadata value. If not specified null will be used by default. NOTE that if you have previously written a record with metadata and a subsequent write does not supply metadata, the metadata associated with the row will be null. Therefore, if you wish to have metadata associated with every write operation, you must supply a valid JSON construct to this method.

      Parameters:
      rowMetadata - the row metadata, must be null or a valid JSON construct: object, array, string, number, true, false or null, otherwise an IllegalArgumentException is thrown.
      Returns:
      this
      Throws:
      IllegalArgumentException - if rowMetadata not null and invalid JSON construct
      Since:
      5.4.18

    • getRowMetadata

      public String getRowMetadata()
      This method is **EXPERIMENTAL** and its behavior, signature, or even its existence may change without prior notice in future versions. Use with caution.

      Returns the row metadata set for this request, or null if not set.

      Returns:
      the row metadata
      Since:
      5.4.18

    • setTimeout

      public QueryRequest setTimeout(int timeoutMs)
      Sets the request timeout value, in milliseconds. This overrides any default value set with NoSQLHandleConfig.setRequestTimeout(int). The value must be positive.
      Parameters:
      timeoutMs - the timeout value, in milliseconds
      Returns:
      this
      Throws:
      IllegalArgumentException - if the timeout value is less than or equal to 0

    • setNamespace

      public QueryRequest setNamespace(String namespace)
      Sets the optional namespace. On-premises only. This overrides any default value set with NoSQLHandleConfig.setDefaultNamespace(java.lang.String). Note: if a namespace is specified in the table name in the SQL statement (using the namespace:tablename format), that value will override this setting.
      Parameters:
      namespace - the namespace to use for the operation
      Returns:
      this
      Since:
      5.4.10

    • getTimeout

      public int getTimeout()
      Returns the timeout to use for the operation, in milliseconds. A value of 0 indicates that the timeout has not been set.
      Returns:
      the value

    • getNumberOfOperations

      public int getNumberOfOperations()
      Returns the total number of operations in a coordinated parallel query operation or 0 if this is not a parallel query.
      Returns:
      the number of operations
      Since:
      5.4.18

    • getOperationNumber

      public int getOperationNumber()
      Returns the individual operation number for this query if it is participating in a coordinated parallel query operation or 0 if not. The value is 1-based.
      Returns:
      the operation number
      Since:
      5.4.18

    • setNumberOfOperations

      public QueryRequest setNumberOfOperations(int numberOfOperations)
      Sets the total number of operations in a coordinated parallel query operation. This value will only be valid if the request contains a prepared query and must be less than or equal to the value returned by PreparedStatement.getMaximumParallelism(). Validation is performed during query execution.
      Parameters:
      numberOfOperations - the number of operations
      Returns:
      this
      Since:
      5.4.18

    • setOperationNumber

      public QueryRequest setOperationNumber(int operationNumber)
      Sets the individual operation number for this query if it is participating in a coordinated parallel query operation. This number must be less than or equal to the total number of operations. The operation number is 1-based and the value will only be valid if the request contains a prepared query. Validation is performed during query execution.
      Parameters:
      operationNumber - the operation number
      Returns:
      this
      Since:
      5.4.18

    • getTypeName

      public String getTypeName()
      Description copied from class: Request
      Returns the type name of the request. This is used for stats.
      Specified by:
      getTypeName in class Request
      Returns:
      the type name of the request