src/kudu/common/partition_pruner.h

// Licensed to the Apache Software Foundation (ASF) under one
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// 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.

#pragma once

#include <cstddef>
#include <string>
#include <vector>

#include <gtest/gtest_prod.h>

#include "kudu/common/partition.h"
#include "kudu/gutil/macros.h"

namespace kudu {

class ScanSpec;
class Schema;

// Provides partition key ranges to a scanner in order to prune tablets which
// are not necessary for the scan. The scanner retrieves the partition key of
// the next tablet to scan through the NextPartitionKey method, and notifies the
// partition pruner that a tablet has been scanned by calling
// RemovePartitionKeyRange with the tablet's upper bound partition key.
//
// Partition keys are in the same encoded format as used by the Partition class.
class PartitionPruner {
 public:
  PartitionPruner() = default;

  // Initializes the partition pruner for a new scan. The scan spec should
  // already be optimized by the ScanSpec::Optimize method.
  void Init(const Schema& schema,
            const PartitionSchema& partition_schema,
            const ScanSpec& scan_spec);

  // Returns whether there are more partition key ranges to scan.
  bool HasMorePartitionKeyRanges() const;

  // Returns the inclusive lower bound partition key of the next tablet to scan.
  const PartitionKey& NextPartitionKey() const;

  // Removes all partition key ranges through the provided exclusive upper bound.
  void RemovePartitionKeyRange(const PartitionKey& upper_bound);

  // Returns true if the provided partition should be pruned.
  bool ShouldPrune(const Partition& partition) const;

  // Returns the number of partition key ranges remaining in the scan.
  size_t NumRangesRemaining() const {
    return partition_key_ranges_.size();
  }

  // Returns a text description of this partition pruner suitable for debug
  // printing.
  std::string ToString(const Schema& schema, const PartitionSchema& partition_schema) const;

 private:
  friend class PartitionPrunerRangeSetTest;
  FRIEND_TEST(PartitionPrunerRangeSetTest, PrepareRangeSet);

  struct RangeBounds {
    std::string lower;
    std::string upper;
  };

  struct PartitionKeyRange {
    PartitionKey start;
    PartitionKey end;
  };

  // Search all combinations of in-list and equality predicates.
  // Return hash values bitset of these combinations.
  static std::vector<bool> PruneHashComponent(
      const PartitionSchema::HashDimension& hash_dimension,
      const Schema& schema,
      const ScanSpec& scan_spec);

  // Given the range bounds and the hash schema, constructs a set of partition
  // key ranges.
  static std::vector<PartitionKeyRange> ConstructPartitionKeyRanges(
      const Schema& schema,
      const ScanSpec& scan_spec,
      const PartitionSchema::HashSchema& hash_schema,
      const RangeBounds& range_bounds);

  // Produce the preliminary set of scanner ranges with proper hash schemas
  // per each range for the scan range defined by 'scan_lower_bound' and
  // 'scan_upper_bound'. The method uses the information on the table-wide hash
  // schema and the range-specific hash schemas provided with
  // 'table_wide_hash_schema' and 'ranges_with_custom_hash_schemas'
  // correspondingly.
  //
  // The predicate-based range is split into sub-ranges that are assigned
  // corresponding hash schemas to them.  In essence, the hash schemas for the
  // ranges with custom hash schemas are known from the
  // 'ranges_with_custom_hash_schemas' parameter, and the rest of the sub-ranges
  // have the table-wide hash schema.
  static void PrepareRangeSet(
    const std::string& scan_lower_bound,
    const std::string& scan_upper_bound,
    const PartitionSchema::HashSchema& table_wide_hash_schema,
    const PartitionSchema::RangesWithHashSchemas& ranges_with_custom_hash_schemas,
    PartitionSchema::RangesWithHashSchemas* ranges);

  // The reverse sorted set of partition key ranges. Each range
  // has an inclusive lower bound and an exclusive upper bound.
  std::vector<PartitionKeyRange> partition_key_ranges_;

  DISALLOW_COPY_AND_ASSIGN(PartitionPruner);
};

} // namespace kudu