clintropolis commented on code in PR #12388: URL: https://github.com/apache/druid/pull/12388#discussion_r866689218
########## processing/src/main/java/org/apache/druid/segment/column/ColumnIndexSupplier.java: ########## @@ -0,0 +1,55 @@ +/* + * 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.druid.segment.column; + +import javax.annotation.Nullable; + +/** + * Provides indexes and information about them ({@link ColumnIndexCapabilities}) for a column. Indexes which satisfy + * the {@link org.apache.druid.query.filter.Filter} used in a {@link org.apache.druid.query.Query}, allow the query + * engine to construct {@link org.apache.druid.segment.data.Offset} (and + * {@link org.apache.druid.segment.vector.VectorOffset}) to build {@link org.apache.druid.segment.Cursor} + * (and {@link org.apache.druid.segment.vector.VectorCursor}). This allows the engine to only scan the rows which match + * the filter values, instead of performing a full scan of the column and using a + * {@link org.apache.druid.query.filter.ValueMatcher} + * (or {@link org.apache.druid.query.filter.vector.VectorValueMatcher}) to filter the values (or in addition to, in the + * case of indexes which {@link ColumnIndexCapabilities#isExact()} is false, which must still use a value matcher + * when using an index). + */ +public interface ColumnIndexSupplier +{ + /** + * Get the {@link ColumnIndexCapabilities} for the specified type of index. If the index does not exist + * this method will return null. A null return value from this method indicates that an index of the desired type + * in unavailable. + */ + @Nullable + <T> ColumnIndexCapabilities getIndexCapabilities(Class<T> clazz); + + /** + * Get a column 'index' of the specified type. If the index of the desired type is not available, this method will + * return null. If the value is non-null, the index may be used for the eventual construction of an + * {@link org.apache.druid.segment.data.Offset} to form the basis of a {@link org.apache.druid.segment.Cursor} + * (or {@link org.apache.druid.segment.vector.VectorOffset} and {@link org.apache.druid.segment.vector.VectorCursor}) + * which can greatly reduce the total number of rows which need to be scanned and processed. + */ + @Nullable + <T> T getIndex(Class<T> clazz); Review Comment: oops, I meant to rename this back to `as` after the changes from the first round of reviews, it only called it `getIndex` because `as` seemed strange when the interface also had `getIndexCapabilities`, so I've renamed this method to `as`. I actually want to work on reclaiming the word 'index' to primarily be used for filtering/cursors so that the codebase is more 'friendly', but not in this PR. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
