lbug 0.15.4

An in-process property graph database management system built for query speed and scalability
Documentation 
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
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291

#include "common/null_mask.h"

#include <algorithm>
#include <cstring>
#include <utility>

#include "common/assert.h"
#include <bit>

namespace lbug {
namespace common {

void NullMask::setNull(uint64_t* nullEntries, uint32_t pos, bool isNull) {
    auto entryPos = pos >> NUM_BITS_PER_NULL_ENTRY_LOG2;
    auto bitPosInEntry = pos - (entryPos << NUM_BITS_PER_NULL_ENTRY_LOG2);
    if (isNull) {
        nullEntries[entryPos] |= NULL_BITMASKS_WITH_SINGLE_ONE[bitPosInEntry];
    } else {
        nullEntries[entryPos] &= NULL_BITMASKS_WITH_SINGLE_ZERO[bitPosInEntry];
    }
}

bool NullMask::copyNullMask(const uint64_t* srcNullEntries, uint64_t srcOffset,
    uint64_t* dstNullEntries, uint64_t dstOffset, uint64_t numBitsToCopy, bool invert) {
    // From benchmarks using setNull/isNull is faster for up to 3 bits
    // (~4x faster for a single bit copy)
    if (numBitsToCopy <= 3) {
        bool anyNull = false;
        for (size_t i = 0; i < numBitsToCopy; i++) {
            bool isNull = NullMask::isNull(srcNullEntries, srcOffset + i);
            NullMask::setNull(dstNullEntries, dstOffset + i, isNull ^ invert);
            anyNull |= isNull;
        }
        return anyNull;
    }
    // If both offsets are aligned relative to each other then copy up to the first byte using the
    // non-aligned method, then copy aligned, then copy the end unaligned again.
    if (!invert && (srcOffset % 8 == dstOffset % 8) && numBitsToCopy >= 8 &&
        numBitsToCopy - (srcOffset % 8) >= 8) {
        auto numBitsInFirstByte = 0;
        bool hasNullInSrcNullMask = false;
        if (srcOffset != 0) {
            numBitsInFirstByte = 8 - (srcOffset % 8);
            if (copyUnaligned(srcNullEntries, srcOffset, dstNullEntries, dstOffset,
                    numBitsInFirstByte, false)) {
                hasNullInSrcNullMask = true;
            }
        }
        auto* src =
            reinterpret_cast<const uint8_t*>(srcNullEntries) + (srcOffset + numBitsInFirstByte) / 8;
        auto* dst =
            reinterpret_cast<uint8_t*>(dstNullEntries) + (dstOffset + numBitsInFirstByte) / 8;
        auto numBytesForAlignedCopy = (numBitsToCopy - numBitsInFirstByte) / 8;
        memcpy(dst, src, numBytesForAlignedCopy);
        if (std::any_of(src, src + numBytesForAlignedCopy, [&](uint8_t val) { return val != 0; })) {
            hasNullInSrcNullMask = true;
        }
        auto lastByteStart = numBitsInFirstByte + numBytesForAlignedCopy * 8;
        auto numBitsInLastByte = numBitsToCopy - numBitsInFirstByte - numBytesForAlignedCopy * 8;
        if (numBitsInLastByte > 0) {
            return copyUnaligned(srcNullEntries, srcOffset + lastByteStart, dstNullEntries,
                       dstOffset + lastByteStart, numBitsInLastByte, false) ||
                   hasNullInSrcNullMask;
        } else {
            return hasNullInSrcNullMask;
        }
    } else {
        return copyUnaligned(srcNullEntries, srcOffset, dstNullEntries, dstOffset, numBitsToCopy,
            invert);
    }
}

bool NullMask::copyUnaligned(const uint64_t* srcNullEntries, uint64_t srcOffset,
    uint64_t* dstNullEntries, uint64_t dstOffset, uint64_t numBitsToCopy, bool invert) {
    uint64_t bitPos = 0;
    bool hasNullInSrcNullMask = false;
    auto [srcNullEntryPos, srcNullBitPos] = getNullEntryAndBitPos(srcOffset + bitPos);
    auto [dstNullEntryPos, dstNullBitPos] = getNullEntryAndBitPos(dstOffset + bitPos);
    while (bitPos < numBitsToCopy) {
        auto curDstNullEntryPos = dstNullEntryPos;
        auto curDstNullBitPos = dstNullBitPos;
        uint64_t numBitsToReadInCurrentEntry = 0;
        uint64_t srcNullMaskEntry =
            invert ? ~srcNullEntries[srcNullEntryPos] : srcNullEntries[srcNullEntryPos];
        if (dstNullBitPos < srcNullBitPos) {
            numBitsToReadInCurrentEntry =
                std::min(NullMask::NUM_BITS_PER_NULL_ENTRY - srcNullBitPos, numBitsToCopy - bitPos);
            // Mask higher bits out of current read range to 0.
            srcNullMaskEntry &= ~NULL_HIGH_MASKS[NullMask::NUM_BITS_PER_NULL_ENTRY -
                                                 (srcNullBitPos + numBitsToReadInCurrentEntry)];
            // Shift right to align the bit in the src and dst entry.
            srcNullMaskEntry = srcNullMaskEntry >> (srcNullBitPos - dstNullBitPos);
            // Mask lower bits out of current read range to 0.
            srcNullMaskEntry &= ~NULL_LOWER_MASKS[dstNullBitPos];
            // Move to the next null entry in src null mask.
            srcNullEntryPos++;
            srcNullBitPos = 0;
            dstNullBitPos += numBitsToReadInCurrentEntry;
        } else if (dstNullBitPos > srcNullBitPos) {
            numBitsToReadInCurrentEntry =
                std::min(NullMask::NUM_BITS_PER_NULL_ENTRY - dstNullBitPos, numBitsToCopy - bitPos);
            // Mask lower bits out of current read range to 0.
            srcNullMaskEntry &= ~NULL_LOWER_MASKS[srcNullBitPos];
            // Shift left to align the bit in the src and dst entry.
            srcNullMaskEntry = srcNullMaskEntry << (dstNullBitPos - srcNullBitPos);
            // Mask higher bits out of current read range to 0.
            srcNullMaskEntry &= ~NULL_HIGH_MASKS[NullMask::NUM_BITS_PER_NULL_ENTRY -
                                                 (dstNullBitPos + numBitsToReadInCurrentEntry)];
            // Move to the next null entry in dst null mask.
            dstNullEntryPos++;
            dstNullBitPos = 0;
            srcNullBitPos += numBitsToReadInCurrentEntry;
        } else {
            numBitsToReadInCurrentEntry =
                std::min(NullMask::NUM_BITS_PER_NULL_ENTRY - dstNullBitPos, numBitsToCopy - bitPos);
            // Mask lower bits out of current read range to 0.
            srcNullMaskEntry &= ~NULL_LOWER_MASKS[srcNullBitPos];
            // Mask higher bits out of current read range to 0.
            srcNullMaskEntry &= ~NULL_HIGH_MASKS[NullMask::NUM_BITS_PER_NULL_ENTRY -
                                                 (dstNullBitPos + numBitsToReadInCurrentEntry)];
            // The input entry and the result entry are already aligned.
            srcNullEntryPos++;
            dstNullEntryPos++;
            srcNullBitPos = dstNullBitPos = 0;
        }
        bitPos += numBitsToReadInCurrentEntry;
        dstNullEntries[curDstNullEntryPos] &=
            ~(NULL_LOWER_MASKS[numBitsToReadInCurrentEntry] << curDstNullBitPos);
        if (srcNullMaskEntry != 0) {
            dstNullEntries[curDstNullEntryPos] |= srcNullMaskEntry;
            hasNullInSrcNullMask = true;
        }
    }
    return hasNullInSrcNullMask;
}

void NullMask::resize(uint64_t capacity) {
    auto numNullEntries = (capacity + NUM_BITS_PER_NULL_ENTRY - 1) / NUM_BITS_PER_NULL_ENTRY;
    auto resizedBuffer = std::make_unique<uint64_t[]>(numNullEntries);
    memcpy(resizedBuffer.get(), data.data(), data.size_bytes());
    buffer = std::move(resizedBuffer);
    data = std::span(buffer.get(), numNullEntries);
}

bool NullMask::copyFromNullBits(const uint64_t* srcNullEntries, uint64_t srcOffset,
    uint64_t dstOffset, uint64_t numBitsToCopy, bool invert) {
    DASSERT(dstOffset + numBitsToCopy <= getNumNullBits(data));
    if (copyNullMask(srcNullEntries, srcOffset, this->data.data(), dstOffset, numBitsToCopy,
            invert)) {
        this->mayContainNulls = true;
        return true;
    }
    return false;
}

void NullMask::setNullFromRange(uint64_t offset, uint64_t numBitsToSet, bool isNull) {
    if (isNull) {
        this->mayContainNulls = true;
    }
    DASSERT(offset + numBitsToSet <= getNumNullBits(data));
    setNullRange(data.data(), offset, numBitsToSet, isNull);
}

void NullMask::setNullRange(uint64_t* nullEntries, uint64_t offset, uint64_t numBitsToSet,
    bool isNull) {
    if (numBitsToSet == 0) {
        return;
    }

    auto [firstEntryPos, firstBitPos] = getNullEntryAndBitPos(offset);
    auto [lastEntryPos, lastBitPos] = getNullEntryAndBitPos(offset + numBitsToSet);

    // If the range spans multiple entries, set the entries in the middle to the appropriate value
    // with std::fill
    if (lastEntryPos > firstEntryPos + 1) {
        std::fill(nullEntries + firstEntryPos + 1, nullEntries + lastEntryPos,
            isNull ? ALL_NULL_ENTRY : NO_NULL_ENTRY);
    }

    if (firstEntryPos == lastEntryPos) {
        if (isNull) {
            // Set bits between the first and the last bit pos to true
            nullEntries[firstEntryPos] |= (~NULL_LOWER_MASKS[firstBitPos] &
                                           ~NULL_HIGH_MASKS[NUM_BITS_PER_NULL_ENTRY - lastBitPos]);
        } else {
            // Set bits between the first and the last bit pos to false
            nullEntries[firstEntryPos] &= (NULL_LOWER_MASKS[firstBitPos] |
                                           NULL_HIGH_MASKS[NUM_BITS_PER_NULL_ENTRY - lastBitPos]);
        }
    } else {
        if (isNull) {
            // Set bits including and after the first bit pos to true
            nullEntries[firstEntryPos] |= ~NULL_LOWER_MASKS[firstBitPos];
            if (lastBitPos > 0) {
                // Set bits before the last bit pos to true
                nullEntries[lastEntryPos] |= NULL_LOWER_MASKS[lastBitPos];
            }
        } else {
            // Set bits including and after the first bit pos to false
            nullEntries[firstEntryPos] &= NULL_LOWER_MASKS[firstBitPos];
            if (lastBitPos > 0) {
                // Set bits before the last bit pos to false
                nullEntries[lastEntryPos] &= ~NULL_LOWER_MASKS[lastBitPos];
            }
        }
    }
}

void NullMask::operator|=(const NullMask& other) {
    DASSERT(other.data.size() == data.size());
    for (size_t i = 0; i < data.size(); i++) {
        data[i] |= other.getData()[i];
    }
}

std::pair<bool, bool> NullMask::getMinMax(const uint64_t* nullEntries, uint64_t offset,
    uint64_t numValues) {
    nullEntries += offset / NUM_BITS_PER_NULL_ENTRY;
    offset = offset % NUM_BITS_PER_NULL_ENTRY;

    // If the offset+numValues are both within a word, just combine the appropriate masks and
    // compare to 0/mask to determine if they are all 1s/all 0s (else a mix)
    if (offset + numValues <= NUM_BITS_PER_NULL_ENTRY) {
        auto mask = NULL_HIGH_MASKS[NUM_BITS_PER_NULL_ENTRY - offset] &
                    NULL_LOWER_MASKS[offset + numValues];
        auto masked = *nullEntries & mask;
        if (masked == 0) {
            return std::make_pair(false, false);
        } else if (masked == mask) {
            return std::make_pair(true, true);
        } else {
            return std::make_pair(false, true);
        }
    }
    // If the range spans multiple entries, check the first one by masking the start
    bool min = false, max = false;
    if (offset > 0) {
        auto mask = NULL_HIGH_MASKS[NUM_BITS_PER_NULL_ENTRY - offset];
        auto masked = *nullEntries & mask;
        if (masked == 0) {
            min = max = false;
        } else if (masked == mask) {
            min = max = true;
        } else {
            return std::make_pair(false, true);
        }
        nullEntries++;
        numValues -= NUM_BITS_PER_NULL_ENTRY - offset;
    } else {
        // Rest of the entry will be checked in the loop below
        min = max = isNull(nullEntries, 0);
    }

    // Check central full bytes, which can be compared in a single operation since we don't ignore
    // any bits If there was no offset, then we calculate the baseline based on the first bit, and
    // compare that to the actual entry
    auto baseline = min ? ~static_cast<uint64_t>(0) : 0;
    for (size_t i = 0; i < numValues / NUM_BITS_PER_NULL_ENTRY; i++) {
        if (nullEntries[i] != baseline) {
            return std::make_pair(false, true);
        }
    }
    nullEntries += numValues / NUM_BITS_PER_NULL_ENTRY;
    numValues = numValues % NUM_BITS_PER_NULL_ENTRY;
    if (numValues > 0) {
        // Check last entry
        auto mask = NULL_LOWER_MASKS[numValues];
        auto masked = *nullEntries & mask;
        if (masked == 0) {
            return std::make_pair(false, max);
        } else if (masked == mask) {
            return std::make_pair(min, true);
        } else {
            return std::make_pair(false, true);
        }
    }
    return std::make_pair(min, max);
}

uint64_t NullMask::countNulls() const {
    // If capacity % 64 != 0 then there may be unused bits at the end of the last entry,
    // but these should always be 0.
    uint64_t sum = 0;
    for (auto entry : data) {
        sum += std::popcount(entry);
    }
    return sum;
}

} // namespace common
} // namespace lbug