blob: 14572728d80963c1a111cbb5eda436e19a6d926f (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
|
// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <vespa/document/bucket/bucketid.h>
#include <vespa/vespalib/util/sync.h>
#include <vector>
namespace vdslib {
/**
* Stable algorithmic hash distribution; this class assigns hash buckets to targets. The number of hash buckets should
* be large compared to the number of targets. The mapping from hash value to hash bucket is performed outside this
* class.
*/
class BucketDistribution {
public:
/**
* Constructs a new bucket distribution object with a given number of columns and buckets.
*
* @param numColumns The number of columns to distribute to.
* @param numBucketBits The number of bits to use for bucket id.
*/
BucketDistribution(uint32_t numColumns, uint32_t numBucketBits);
BucketDistribution(const BucketDistribution &);
BucketDistribution & operator = (const BucketDistribution &);
BucketDistribution(BucketDistribution &&) = default;
BucketDistribution & operator = (BucketDistribution &&) = default;
~BucketDistribution();
/**
* Returns the number of buckets that the given number of bucket bits will allow.
*
* @param numBucketBits The number of bits to use for bucket id.
* @return The number of buckets allowed.
*/
static uint32_t getNumBuckets(uint32_t numBucketBits) { return 1 << numBucketBits; }
/**
* This method returns a list that contains the distributions of the given number of buckets over the given number
* of columns.
*
* @param numColumns The number of columns to distribute to.
* @param numBucketBits The number of bits to use for bucket id.
* @param ret List to fill with the bucket distribution.
*/
static void getBucketCount(uint32_t numColumns, uint32_t numBucketBits, std::vector<uint32_t> &ret);
/**
* This method returns a list similar to {@link this#getBucketCount(int,int)}, except that the returned list
* contains the number of buckets that will have to be migrated from each column if an additional column was added.
*
* @param numColumns The original number of columns.
* @param numBucketBits The number of bits to use for bucket id.
* @param ret List to fill with the number of buckets to migrate, one value per column.
*/
static void getBucketMigrateCount(uint32_t numColumns, uint32_t numBucketBits, std::vector<uint32_t> &ret);
/**
* Sets the number of columns to distribute to to 1, and resets the content of the internal bucket-to-column map so
* that it all buckets point to that single column.
*/
void reset();
/**
* Sets the number of columns to use for this document distribution object. This will reset and setup this object
* from scratch. The original number of buckets is maintained.
*
* @param numColumns The new number of columns to distribute to.
*/
void setNumColumns(uint32_t numColumns);
/**
* Returns the number of columns to distribute to.
*
* @return The number of columns.
*/
uint32_t getNumColumns() const { return _numColumns; }
/**
* Sets the number of buckets to use for this document distribution object. This will reset and setup this object
* from scratch. The original number of columns is maintained.
*
* @param numBucketBits The new number of bits to use for bucket id.
*/
void setNumBucketBits(uint32_t numBucketBits);
/**
* Returns the number of bits used for bucket identifiers.
*
* @return The number of bits.
*/
uint32_t getNumBucketBits() const { return _numBucketBits; }
/**
* Returns the number of buckets available using the configured number of bucket bits.
*
* @return The number of buckets.
*/
uint32_t getNumBuckets() const { return getNumBuckets(_numBucketBits); }
/**
* This method maps the given bucket id to its corresponding column.
*
* @param bucketId The bucket whose column to lookup.
* @return The column to distribute the bucket to.
*/
uint32_t getColumn(const document::BucketId &bucketId) const;
private:
/**
* Adds a single column to this bucket distribution object. This will modify the internal bucket-to-column map so
* that it takes into account the new column.
*/
void addColumn();
private:
uint32_t _numColumns; // The number of columns to distribute to.
uint32_t _numBucketBits; // The number of bits to use for bucket identification.
std::vector<uint32_t> _bucketToColumn; // A map from bucket id to column index.
vespalib::Lock _lock;
};
}
|
