| // Licensed to the Apache Software Foundation (ASF) under one |
| // or more contributor license agreements. See the NOTICE file |
| // distributed with this work for additional information |
| // regarding copyright ownership. The ASF licenses this file |
| // to you under the Apache License, Version 2.0 (the |
| // "License"); you may not use this file except in compliance |
| // with the License. You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, |
| // software distributed under the License is distributed on an |
| // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| // KIND, either express or implied. See the License for the |
| // specific language governing permissions and limitations |
| // under the License. |
| |
| package org.apache.impala.extdatasource.v1; |
| |
| import org.apache.impala.extdatasource.thrift.TCloseParams; |
| import org.apache.impala.extdatasource.thrift.TCloseResult; |
| import org.apache.impala.extdatasource.thrift.TGetNextParams; |
| import org.apache.impala.extdatasource.thrift.TGetNextResult; |
| import org.apache.impala.extdatasource.thrift.TOpenParams; |
| import org.apache.impala.extdatasource.thrift.TOpenResult; |
| import org.apache.impala.extdatasource.thrift.TPrepareParams; |
| import org.apache.impala.extdatasource.thrift.TPrepareResult; |
| |
| /** |
| * Defines an external data source. Called by Impala during planning (prepare() only) |
| * and during query execution (open(), getNext(), and close()). |
| * TODO: Add javadocs |
| */ |
| public interface ExternalDataSource { |
| |
| /** |
| * Called during the planning phase and serves two purposes: |
| * 1) to pass information to the query planner for a specific scan operation (right |
| * now only an estimate of the number of rows returned). |
| * 2) to accept or reject predicates that are present in the query; accepted |
| * predicates are then handed over to the library when the scan is initiated with |
| * the Open() call. |
| * If prepare() fails, query planning will return with an error. |
| */ |
| TPrepareResult prepare(TPrepareParams params); |
| |
| /** |
| * Starts a scan. Called during query execution before any calls to getNext(). |
| */ |
| TOpenResult open(TOpenParams params); |
| |
| /** |
| * Gets the next row batch of the scan. |
| */ |
| TGetNextResult getNext(TGetNextParams params); |
| |
| /** |
| * Ends the scan. After this call Impala will not make any more getNext() calls for |
| * this same handle and the implementation is free to release all related resources. |
| * Can be called at any point after open() has been called, even if the scan itself |
| * hasn't finished (TGetNextResult.eos was not set to true). |
| * Should always be called once unless prepare() fails. |
| */ |
| TCloseResult close(TCloseParams params); |
| } |