/usr/share/gocode/src/github.com/couchbase/moss/segment_index.go is in golang-github-couchbase-moss-dev 0.0~git20170914.0.07c86e8-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 | // Copyright (c) 2017 Couchbase, Inc.
//
// Licensed 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 moss
import (
"bytes"
)
type segmentKeysIndex struct {
// Number of keys that can be indexed.
numIndexableKeys int
// Keys that have been added so far.
numKeys int
// Size in bytes of all the indexed keys.
numKeyBytes int
// In-memory byte array of keys.
data []byte
// Start offsets of keys in the data array.
offsets []uint32
// Number of skips over keys in the segment kvs to arrive at the
// next adjacent key in the data array.
hop int
// Total number of keys in the source segment.
srcKeyCount int
}
// newSegmentKeysIndex preallocates the data/offsets arrays
// based on a calculated hop.
func newSegmentKeysIndex(quota int, srcKeyCount int,
keyAvgSize int) *segmentKeysIndex {
numIndexableKeys := quota / (keyAvgSize + 4 /* 4 for the offset */)
if numIndexableKeys == 0 {
return nil
}
hop := (srcKeyCount / numIndexableKeys) + 1
data := make([]byte, numIndexableKeys*keyAvgSize)
offsets := make([]uint32, numIndexableKeys)
return &segmentKeysIndex{
numIndexableKeys: numIndexableKeys,
numKeys: 0,
numKeyBytes: 0,
data: data,
offsets: offsets,
hop: hop,
srcKeyCount: srcKeyCount,
}
}
// Adds a qualified entry to the index. Returns true if space
// still available, false otherwise.
func (s *segmentKeysIndex) add(keyIdx int, key []byte) bool {
if s.numKeys >= s.numIndexableKeys {
// All keys that can be indexed already have been,
// return false indicating that there's no room for
// anymore.
return false
}
if len(key) > (len(s.data) - s.numKeyBytes) {
// No room for any more keys.
return false
}
if keyIdx%(s.hop) != 0 {
// Key does not satisfy the hop condition.
return true
}
s.offsets[s.numKeys] = uint32(s.numKeyBytes)
copy(s.data[s.numKeyBytes:], key)
s.numKeys++
s.numKeyBytes += len(key)
return true
}
// Fetches the range of offsets between which the key exists,
// if present at all. The returned leftPos and rightPos can
// directly be used as the left and right extreme cursors
// while binary searching over the source segment.
func (s *segmentKeysIndex) lookup(key []byte) (leftPos int, rightPos int) {
i, j := 0, s.numKeys
if i == j || s.numKeys < 2 {
// The index either wasn't used or isn't of any use.
rightPos = s.srcKeyCount
return
}
// If key smaller than the first key, return early.
keyStart := s.offsets[0]
keyEnd := s.offsets[1]
cmp := bytes.Compare(key, s.data[keyStart:keyEnd])
if cmp < 0 {
// ENOENT.
return
}
indexOfLastKey := s.numKeys - 1
// If key larger than last key, return early.
keyStart = s.offsets[indexOfLastKey]
keyEnd = uint32(s.numKeyBytes)
cmp = bytes.Compare(s.data[keyStart:keyEnd], key)
if cmp < 0 {
leftPos = (indexOfLastKey) * s.hop
rightPos = s.srcKeyCount
return
}
for i < j {
h := i + (j-i)/2
keyStart = s.offsets[h]
if h < indexOfLastKey {
keyEnd = s.offsets[h+1]
} else {
keyEnd = uint32(s.numKeyBytes)
}
cmp = bytes.Compare(s.data[keyStart:keyEnd], key)
if cmp == 0 {
// Direct hit.
leftPos = h * s.hop
rightPos = leftPos + 1
return
} else if cmp < 0 {
if i == h {
break
}
i = h
} else {
j = h
}
}
leftPos = i * s.hop
rightPos = j * s.hop
return
}
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