vitess.io/vitess@v0.16.2/go/vt/vtgate/vindexes/xxhash.go (about)

     1  /*
     2  Copyright 2019 The Vitess Authors.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package vindexes
    18  
    19  import (
    20  	"bytes"
    21  	"context"
    22  	"encoding/binary"
    23  
    24  	"github.com/cespare/xxhash/v2"
    25  
    26  	"vitess.io/vitess/go/sqltypes"
    27  	"vitess.io/vitess/go/vt/key"
    28  )
    29  
    30  var (
    31  	_ SingleColumn = (*XXHash)(nil)
    32  	_ Hashing      = (*XXHash)(nil)
    33  )
    34  
    35  // XXHash defines vindex that hashes any sql types to a KeyspaceId
    36  // by using xxhash64. It's Unique and works on any platform giving identical result.
    37  type XXHash struct {
    38  	name string
    39  }
    40  
    41  // NewXXHash creates a new XXHash.
    42  func NewXXHash(name string, _ map[string]string) (Vindex, error) {
    43  	return &XXHash{name: name}, nil
    44  }
    45  
    46  // String returns the name of the vindex.
    47  func (vind *XXHash) String() string {
    48  	return vind.name
    49  }
    50  
    51  // Cost returns the cost of this index as 1.
    52  func (vind *XXHash) Cost() int {
    53  	return 1
    54  }
    55  
    56  // IsUnique returns true since the Vindex is unique.
    57  func (vind *XXHash) IsUnique() bool {
    58  	return true
    59  }
    60  
    61  // NeedsVCursor satisfies the Vindex interface.
    62  func (vind *XXHash) NeedsVCursor() bool {
    63  	return false
    64  }
    65  
    66  // Map can map ids to key.Destination objects.
    67  func (vind *XXHash) Map(ctx context.Context, vcursor VCursor, ids []sqltypes.Value) ([]key.Destination, error) {
    68  	out := make([]key.Destination, 0, len(ids))
    69  	for _, id := range ids {
    70  		ksid, err := vind.Hash(id)
    71  		if err != nil {
    72  			return nil, err
    73  		}
    74  		out = append(out, key.DestinationKeyspaceID(ksid))
    75  	}
    76  	return out, nil
    77  }
    78  
    79  // Verify returns true if ids maps to ksids.
    80  func (vind *XXHash) Verify(ctx context.Context, vcursor VCursor, ids []sqltypes.Value, ksids [][]byte) ([]bool, error) {
    81  	out := make([]bool, 0, len(ids))
    82  	for i, id := range ids {
    83  		ksid, err := vind.Hash(id)
    84  		if err != nil {
    85  			return out, err
    86  		}
    87  		out = append(out, bytes.Equal(ksid, ksids[i]))
    88  	}
    89  	return out, nil
    90  }
    91  
    92  func (vind *XXHash) Hash(id sqltypes.Value) ([]byte, error) {
    93  	idBytes, err := id.ToBytes()
    94  	if err != nil {
    95  		return nil, err
    96  	}
    97  	return vXXHash(idBytes), nil
    98  }
    99  
   100  func init() {
   101  	Register("xxhash", NewXXHash)
   102  }
   103  
   104  func vXXHash(shardKey []byte) []byte {
   105  	var hashed [8]byte
   106  	hashKey := xxhash.Sum64(shardKey)
   107  	binary.LittleEndian.PutUint64(hashed[:], hashKey)
   108  	return hashed[:]
   109  }