content: /*
   * 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.cassandra.io.sstable;
  
  import org.apache.cassandra.io.sstable.format.SSTableReader;
  import org.apache.cassandra.tracing.Tracing;
  
  /**
   * Listener for receiving notifications associated with reading SSTables.
   */
  public interface SSTableReadsListener
  {
      /**
       * The reasons for skipping an SSTable
       */
      enum SkippingReason
      {
          BLOOM_FILTER("Bloom filter allows skipping sstable {}"),
          MIN_MAX_KEYS("Check against min and max keys allows skipping sstable {}"),
          PARTITION_INDEX_LOOKUP("Partition index lookup allows skipping sstable {}"),
          INDEX_ENTRY_NOT_FOUND("Partition index lookup complete (bloom filter false positive) for sstable {}");
  
          private final String message;
  
          SkippingReason(String message)
          {
              this.message = message;
          }
  
          public void trace(Descriptor descriptor)
          {
              Tracing.trace(message, descriptor.id);
          }
      }
  
      /**
       * The reasons for selecting an SSTable
       */
      enum SelectionReason
      {
          KEY_CACHE_HIT("Key cache hit for sstable {}, size = {}"),
          INDEX_ENTRY_FOUND("Partition index found for sstable {}, size = {}");
  
          private final String message;
  
          SelectionReason(String message)
          {
              this.message = message;
          }
  
          public void trace(Descriptor descriptor, AbstractRowIndexEntry entry)
          {
              Tracing.trace(message, descriptor.id, entry.blockCount());
          }
      }
  
      /**
       * Listener that does nothing.
       */
      static final SSTableReadsListener NOOP_LISTENER = new SSTableReadsListener() {};
  
      /**
       * Handles notification that the specified SSTable has been skipped during a single partition query.
       *
       * @param sstable the SSTable reader
       * @param reason the reason for which the SSTable has been skipped
       */
      default void onSSTableSkipped(SSTableReader sstable, SkippingReason reason)
      {
      }
  
      /**
       * Handles notification that the specified SSTable has been selected during a single partition query.
       *
       * @param sstable the SSTable reader
       * @param indexEntry the index entry
       * @param reason the reason for which the SSTable has been selected
       */
      default void onSSTableSelected(SSTableReader sstable, SelectionReason reason)
      {
      }
  
      /**
       * Handles notification that the specified SSTable is being scanned during a partition range query.
       *
       * @param sstable the SSTable reader of the SSTable being scanned.
       */
      default void onScanningStarted(SSTableReader sstable)
      {
      }
  }
  