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Merge branch 'hyperloglog-improvement' of https://github.com/oertl/redis into oertl-hyperloglog-improvement

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antirez 2018-03-16 16:27:38 +01:00
commit 7e3c583532
1 changed files with 124 additions and 117 deletions
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233
src/hyperloglog.c
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@ -192,6 +192,8 @@ struct hllhdr {
#define HLL_VALID_CACHE(hdr) (((hdr)->card[7] & (1<<7)) == 0) #define HLL_VALID_CACHE(hdr) (((hdr)->card[7] & (1<<7)) == 0)
#define HLL_P 14 /* The greater is P, the smaller the error. */ #define HLL_P 14 /* The greater is P, the smaller the error. */
#define HLL_Q (64-HLL_P) /* The number of bits of the hash value used for
determining the number of leading zeros. */
#define HLL_REGISTERS (1<<HLL_P) /* With P=14, 16384 registers. */ #define HLL_REGISTERS (1<<HLL_P) /* With P=14, 16384 registers. */
#define HLL_P_MASK (HLL_REGISTERS-1) /* Mask to index register. */ #define HLL_P_MASK (HLL_REGISTERS-1) /* Mask to index register. */
#define HLL_BITS 6 /* Enough to count up to 63 leading zeroes. */ #define HLL_BITS 6 /* Enough to count up to 63 leading zeroes. */
@ -384,6 +386,7 @@ static char *invalid_hll_err = "-INVALIDOBJ Corrupted HLL object detected\r\n";
*(p) = (_l>>8) | HLL_SPARSE_XZERO_BIT; \ *(p) = (_l>>8) | HLL_SPARSE_XZERO_BIT; \
*((p)+1) = (_l&0xff); \ *((p)+1) = (_l&0xff); \
} while(0) } while(0)
#define HLL_ALPHA_INF 0.721347520444481703680 /* constant for 0.5/ln(2) */
/* ========================= HyperLogLog algorithm ========================= */ /* ========================= HyperLogLog algorithm ========================= */
@ -451,7 +454,7 @@ int hllPatLen(unsigned char *ele, size_t elesize, long *regp) {
/* Count the number of zeroes starting from bit HLL_REGISTERS /* Count the number of zeroes starting from bit HLL_REGISTERS
* (that is a power of two corresponding to the first bit we don't use * (that is a power of two corresponding to the first bit we don't use
* as index). The max run can be 64-P+1 bits. * as index). The max run can be 64-P+1 = Q+1 bits.
* *
* Note that the final "1" ending the sequence of zeroes must be * Note that the final "1" ending the sequence of zeroes must be
* included in the count, so if we find "001" the count is 3, and * included in the count, so if we find "001" the count is 3, and
@ -462,8 +465,10 @@ int hllPatLen(unsigned char *ele, size_t elesize, long *regp) {
* there are high probabilities to find a 1 after a few iterations. */ * there are high probabilities to find a 1 after a few iterations. */
hash = MurmurHash64A(ele,elesize,0xadc83b19ULL); hash = MurmurHash64A(ele,elesize,0xadc83b19ULL);
index = hash & HLL_P_MASK; /* Register index. */ index = hash & HLL_P_MASK; /* Register index. */
hash |= ((uint64_t)1<<63); /* Make sure the loop terminates. */ hash >>= HLL_P; /* Remove bits used to address the register. */
bit = HLL_REGISTERS; /* First bit not used to address the register. */ hash |= ((uint64_t)1<<HLL_Q); /* Make sure the loop terminates
and count will be <= Q+1. */
bit = 1;
count = 1; /* Initialized to 1 since we count the "00000...1" pattern. */ count = 1; /* Initialized to 1 since we count the "00000...1" pattern. */
while((hash & bit) == 0) { while((hash & bit) == 0) {
count++; count++;
@ -510,13 +515,9 @@ int hllDenseAdd(uint8_t *registers, unsigned char *ele, size_t elesize) {
return hllDenseSet(registers,index,count); return hllDenseSet(registers,index,count);
} }
/* Compute SUM(2^-reg) in the dense representation. /* Compute the register histogram in the dense representation. */
* PE is an array with a pre-computer table of values 2^-reg indexed by reg. void hllDenseRegHisto(uint8_t *registers, int* regHisto) {
* As a side effect the integer pointed by 'ezp' is set to the number int j;
* of zero registers. */
double hllDenseSum(uint8_t *registers, double *PE, int *ezp) {
double E = 0;
int j, ez = 0;
/* Redis default is to use 16384 registers 6 bits each. The code works /* Redis default is to use 16384 registers 6 bits each. The code works
* with other values by modifying the defines, but for our target value * with other values by modifying the defines, but for our target value
@ -527,47 +528,49 @@ double hllDenseSum(uint8_t *registers, double *PE, int *ezp) {
r10, r11, r12, r13, r14, r15; r10, r11, r12, r13, r14, r15;
for (j = 0; j < 1024; j++) { for (j = 0; j < 1024; j++) {
/* Handle 16 registers per iteration. */ /* Handle 16 registers per iteration. */
r0 = r[0] & 63; if (r0 == 0) ez++; r0 = r[0] & 63;
r1 = (r[0] >> 6 | r[1] << 2) & 63; if (r1 == 0) ez++; r1 = (r[0] >> 6 | r[1] << 2) & 63;
r2 = (r[1] >> 4 | r[2] << 4) & 63; if (r2 == 0) ez++; r2 = (r[1] >> 4 | r[2] << 4) & 63;
r3 = (r[2] >> 2) & 63; if (r3 == 0) ez++; r3 = (r[2] >> 2) & 63;
r4 = r[3] & 63; if (r4 == 0) ez++; r4 = r[3] & 63;
r5 = (r[3] >> 6 | r[4] << 2) & 63; if (r5 == 0) ez++; r5 = (r[3] >> 6 | r[4] << 2) & 63;
r6 = (r[4] >> 4 | r[5] << 4) & 63; if (r6 == 0) ez++; r6 = (r[4] >> 4 | r[5] << 4) & 63;
r7 = (r[5] >> 2) & 63; if (r7 == 0) ez++; r7 = (r[5] >> 2) & 63;
r8 = r[6] & 63; if (r8 == 0) ez++; r8 = r[6] & 63;
r9 = (r[6] >> 6 | r[7] << 2) & 63; if (r9 == 0) ez++; r9 = (r[6] >> 6 | r[7] << 2) & 63;
r10 = (r[7] >> 4 | r[8] << 4) & 63; if (r10 == 0) ez++; r10 = (r[7] >> 4 | r[8] << 4) & 63;
r11 = (r[8] >> 2) & 63; if (r11 == 0) ez++; r11 = (r[8] >> 2) & 63;
r12 = r[9] & 63; if (r12 == 0) ez++; r12 = r[9] & 63;
r13 = (r[9] >> 6 | r[10] << 2) & 63; if (r13 == 0) ez++; r13 = (r[9] >> 6 | r[10] << 2) & 63;
r14 = (r[10] >> 4 | r[11] << 4) & 63; if (r14 == 0) ez++; r14 = (r[10] >> 4 | r[11] << 4) & 63;
r15 = (r[11] >> 2) & 63; if (r15 == 0) ez++; r15 = (r[11] >> 2) & 63;
regHisto[r0] += 1;
regHisto[r1] += 1;
regHisto[r2] += 1;
regHisto[r3] += 1;
regHisto[r4] += 1;
regHisto[r5] += 1;
regHisto[r6] += 1;
regHisto[r7] += 1;
regHisto[r8] += 1;
regHisto[r9] += 1;
regHisto[r10] += 1;
regHisto[r11] += 1;
regHisto[r12] += 1;
regHisto[r13] += 1;
regHisto[r14] += 1;
regHisto[r15] += 1;
/* Additional parens will allow the compiler to optimize the
* code more with a loss of precision that is not very relevant
* here (floating point math is not commutative!). */
E += (PE[r0] + PE[r1]) + (PE[r2] + PE[r3]) + (PE[r4] + PE[r5]) +
(PE[r6] + PE[r7]) + (PE[r8] + PE[r9]) + (PE[r10] + PE[r11]) +
(PE[r12] + PE[r13]) + (PE[r14] + PE[r15]);
r += 12; r += 12;
} }
} else { } else {
for (j = 0; j < HLL_REGISTERS; j++) { for(j = 0; j < HLL_REGISTERS; j++) {
unsigned long reg; unsigned long reg;
HLL_DENSE_GET_REGISTER(reg,registers,j); HLL_DENSE_GET_REGISTER(reg,registers,j);
if (reg == 0) { regHisto[reg] += 1;
ez++;
/* Increment E at the end of the loop. */
} else {
E += PE[reg]; /* Precomputed 2^(-reg[j]). */
} }
} }
E += ez; /* Add 2^0 'ez' times. */
}
*ezp = ez;
return E;
} }
/* ================== Sparse representation implementation ================= */ /* ================== Sparse representation implementation ================= */
@ -903,76 +906,96 @@ int hllSparseAdd(robj *o, unsigned char *ele, size_t elesize) {
return hllSparseSet(o,index,count); return hllSparseSet(o,index,count);
} }
/* Compute SUM(2^-reg) in the sparse representation. /* Compute the register histogram in the sparse representation. */
* PE is an array with a pre-computer table of values 2^-reg indexed by reg. void hllSparseRegHisto(uint8_t *sparse, int sparselen, int *invalid, int* regHisto) {
* As a side effect the integer pointed by 'ezp' is set to the number int idx = 0, runlen, regval;
* of zero registers. */
double hllSparseSum(uint8_t *sparse, int sparselen, double *PE, int *ezp, int *invalid) {
double E = 0;
int ez = 0, idx = 0, runlen, regval;
uint8_t *end = sparse+sparselen, *p = sparse; uint8_t *end = sparse+sparselen, *p = sparse;
while(p < end) { while(p < end) {
if (HLL_SPARSE_IS_ZERO(p)) { if (HLL_SPARSE_IS_ZERO(p)) {
runlen = HLL_SPARSE_ZERO_LEN(p); runlen = HLL_SPARSE_ZERO_LEN(p);
idx += runlen; idx += runlen;
ez += runlen; regHisto[0] += runlen;
/* Increment E at the end of the loop. */
p++; p++;
} else if (HLL_SPARSE_IS_XZERO(p)) { } else if (HLL_SPARSE_IS_XZERO(p)) {
runlen = HLL_SPARSE_XZERO_LEN(p); runlen = HLL_SPARSE_XZERO_LEN(p);
idx += runlen; idx += runlen;
ez += runlen; regHisto[0] += runlen;
/* Increment E at the end of the loop. */
p += 2; p += 2;
} else { } else {
runlen = HLL_SPARSE_VAL_LEN(p); runlen = HLL_SPARSE_VAL_LEN(p);
regval = HLL_SPARSE_VAL_VALUE(p); regval = HLL_SPARSE_VAL_VALUE(p);
idx += runlen; idx += runlen;
E += PE[regval]*runlen; regHisto[regval] += runlen;
p++; p++;
} }
} }
if (idx != HLL_REGISTERS && invalid) *invalid = 1; if (idx != HLL_REGISTERS && invalid) *invalid = 1;
E += ez; /* Add 2^0 'ez' times. */
*ezp = ez;
return E;
} }
/* ========================= HyperLogLog Count ============================== /* ========================= HyperLogLog Count ==============================
* This is the core of the algorithm where the approximated count is computed. * This is the core of the algorithm where the approximated count is computed.
* The function uses the lower level hllDenseSum() and hllSparseSum() functions * The function uses the lower level hllDenseRegHisto() and hllSparseRegHisto()
* as helpers to compute the SUM(2^-reg) part of the computation, which is * functions as helpers to compute histogram of register values part of the
* representation-specific, while all the rest is common. */ * computation, which is representation-specific, while all the rest is common. */
/* Implements the SUM operation for uint8_t data type which is only used /* Implements the register histogram calculation for uint8_t data type
* internally as speedup for PFCOUNT with multiple keys. */ * which is only used internally as speedup for PFCOUNT with multiple keys. */
double hllRawSum(uint8_t *registers, double *PE, int *ezp) { void hllRawRegHisto(uint8_t *registers, int* regHisto) {
double E = 0;
int j, ez = 0;
uint64_t *word = (uint64_t*) registers; uint64_t *word = (uint64_t*) registers;
uint8_t *bytes; uint8_t *bytes;
int j;
for (j = 0; j < HLL_REGISTERS/8; j++) { for (j = 0; j < HLL_REGISTERS/8; j++) {
if (*word == 0) { if (*word == 0) {
ez += 8; regHisto[0] += 8;
} else { } else {
bytes = (uint8_t*) word; bytes = (uint8_t*) word;
if (bytes[0]) E += PE[bytes[0]]; else ez++; regHisto[bytes[0]] += 1;
if (bytes[1]) E += PE[bytes[1]]; else ez++; regHisto[bytes[1]] += 1;
if (bytes[2]) E += PE[bytes[2]]; else ez++; regHisto[bytes[2]] += 1;
if (bytes[3]) E += PE[bytes[3]]; else ez++; regHisto[bytes[3]] += 1;
if (bytes[4]) E += PE[bytes[4]]; else ez++; regHisto[bytes[4]] += 1;
if (bytes[5]) E += PE[bytes[5]]; else ez++; regHisto[bytes[5]] += 1;
if (bytes[6]) E += PE[bytes[6]]; else ez++; regHisto[bytes[6]] += 1;
if (bytes[7]) E += PE[bytes[7]]; else ez++; regHisto[bytes[7]] += 1;
} }
word++; word++;
} }
E += ez; /* 2^(-reg[j]) is 1 when m is 0, add it 'ez' times for every }
zero register in the HLL. */
*ezp = ez; /* Helper function sigma as defined in
return E; * "New cardinality estimation algorithms for HyperLogLog sketches"
* Otmar Ertl, arXiv:1702.01284 */
double hllSigma(double x) {
if (x == 1.) return INFINITY;
double zPrime;
double y = 1;
double z = x;
do {
x *= x;
zPrime = z;
z += x * y;
y += y;
} while(zPrime != z);
return z;
}
/* Helper function tau as defined in
* "New cardinality estimation algorithms for HyperLogLog sketches"
* Otmar Ertl, arXiv:1702.01284 */
double hllTau(double x) {
if (x == 0. || x == 1.) return 0.;
double zPrime;
double y = 1.0;
double z = 1 - x;
do {
x = sqrt(x);
zPrime = z;
y *= 0.5;
z -= pow(1 - x, 2)*y;
} while(zPrime != z);
return z / 3;
} }
/* Return the approximated cardinality of the set based on the harmonic /* Return the approximated cardinality of the set based on the harmonic
@ -988,49 +1011,33 @@ double hllRawSum(uint8_t *registers, double *PE, int *ezp) {
* keys (no need to work with 6-bit integers encoding). */ * keys (no need to work with 6-bit integers encoding). */
uint64_t hllCount(struct hllhdr *hdr, int *invalid) { uint64_t hllCount(struct hllhdr *hdr, int *invalid) {
double m = HLL_REGISTERS; double m = HLL_REGISTERS;
double E, alpha = 0.7213/(1+1.079/m); double E;
int j, ez; /* Number of registers equal to 0. */ int j;
int regHisto[HLL_Q+2] = {0};
/* We precompute 2^(-reg[j]) in a small table in order to /* Compute register histogram */
* speedup the computation of SUM(2^-register[0..i]). */
static int initialized = 0;
static double PE[64];
if (!initialized) {
PE[0] = 1; /* 2^(-reg[j]) is 1 when m is 0. */
for (j = 1; j < 64; j++) {
/* 2^(-reg[j]) is the same as 1/2^reg[j]. */
PE[j] = 1.0/(1ULL << j);
}
initialized = 1;
}
/* Compute SUM(2^-register[0..i]). */
if (hdr->encoding == HLL_DENSE) { if (hdr->encoding == HLL_DENSE) {
E = hllDenseSum(hdr->registers,PE,&ez); hllDenseRegHisto(hdr->registers,regHisto);
} else if (hdr->encoding == HLL_SPARSE) { } else if (hdr->encoding == HLL_SPARSE) {
E = hllSparseSum(hdr->registers, hllSparseRegHisto(hdr->registers,
sdslen((sds)hdr)-HLL_HDR_SIZE,PE,&ez,invalid); sdslen((sds)hdr)-HLL_HDR_SIZE,invalid,regHisto);
} else if (hdr->encoding == HLL_RAW) { } else if (hdr->encoding == HLL_RAW) {
E = hllRawSum(hdr->registers,PE,&ez); hllRawRegHisto(hdr->registers,regHisto);
} else { } else {
serverPanic("Unknown HyperLogLog encoding in hllCount()"); serverPanic("Unknown HyperLogLog encoding in hllCount()");
} }
/* Apply loglog-beta to the raw estimate. See: /* Estimate cardinality form register histogram. See:
* "LogLog-Beta and More: A New Algorithm for Cardinality Estimation * "New cardinality estimation algorithms for HyperLogLog sketches"
* Based on LogLog Counting" Jason Qin, Denys Kim, Yumei Tung * Otmar Ertl, arXiv:1702.01284 */
* arXiv:1612.02284 */ double z = m * hllTau((m-regHisto[HLL_Q+1])/(double)m);
double zl = log(ez + 1); for (j = HLL_Q; j >= 1; --j) {
double beta = -0.370393911*ez + z += regHisto[j];
0.070471823*zl + z *= 0.5;
0.17393686*pow(zl,2) + }
0.16339839*pow(zl,3) + z += m * hllSigma(regHisto[0]/(double)m);
-0.09237745*pow(zl,4) + E = llroundl(HLL_ALPHA_INF*m*m/z);
0.03738027*pow(zl,5) +
-0.005384159*pow(zl,6) +
0.00042419*pow(zl,7);
E = llroundl(alpha*m*(m-ez)*(1/(E+beta)));
return (uint64_t) E; return (uint64_t) E;
} }