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faiss/IndexIVFPQ.cpp

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/**
* Copyright (c) 2015-present, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the CC-by-NC license found in the
* LICENSE file in the root directory of this source tree.
*/
/* Copyright 2004-present Facebook. All Rights Reserved.
Inverted list structure.
*/
#include "IndexIVFPQ.h"
#include <cstdio>
#include <cassert>
#include <sys/mman.h>
#include <algorithm>
#include "Heap.h"
#include "utils.h"
#include "Clustering.h"
#include "IndexFlat.h"
#include "hamming.h"
#include "FaissAssert.h"
#include "AuxIndexStructures.h"
namespace faiss {
/*****************************************
* IndexIVFPQ implementation
******************************************/
IndexIVFPQ::IndexIVFPQ (Index * quantizer, size_t d, size_t nlist,
size_t M, size_t nbits_per_idx):
IndexIVF (quantizer, d, nlist, METRIC_L2),
pq (d, M, nbits_per_idx)
{
FAISS_ASSERT (nbits_per_idx <= 8);
code_size = pq.code_size;
is_trained = false;
codes.resize (nlist);
by_residual = true;
use_precomputed_table = 0;
scan_table_threshold = 0;
max_codes = 0; // means unlimited
polysemous_training = nullptr;
do_polysemous_training = false;
polysemous_ht = 0;
set_typename();
}
void IndexIVFPQ::set_typename ()
{
std::stringstream s;
s << "IvfPQ_" << pq.M << "x" << pq.nbits
<< "[" << nlist << ":" << quantizer->index_typename << "]";
index_typename = s.str();
}
void IndexIVFPQ::train_residual (idx_t n, const float *x)
{
train_residual_o (n, x, nullptr);
}
void IndexIVFPQ::train_residual_o (idx_t n, const float *x, float *residuals_2)
{
idx_t ntrain = pq.ksub * 64;
if(n > ntrain) n = ntrain;
const float *trainset;
if (by_residual) {
if(verbose) printf("computing residuals\n");
idx_t * assign = new idx_t [n]; // assignement to coarse centroids
quantizer->assign (n, x, assign);
float *residuals = new float [n * d];
for (idx_t i = 0; i < n; i++)
quantizer->compute_residual (x + i * d, residuals+i*d, assign[i]);
delete [] assign;
trainset = residuals;
} else {
trainset = x;
}
if (verbose)
printf ("training %zdx%zd product quantizer on %ld vectors in %dD\n",
pq.M, pq.ksub, n, d);
pq.verbose = verbose;
pq.train (n, trainset);
if (do_polysemous_training) {
PolysemousTraining default_pt;
PolysemousTraining *pt = polysemous_training;
if (!pt) pt = &default_pt;
pt->optimize_pq_for_hamming (pq, n, trainset);
}
// prepare second-level residuals for refine PQ
if (residuals_2) {
uint8_t *train_codes = new uint8_t [pq.code_size * n];
pq.compute_codes (trainset, train_codes, n);
for (idx_t i = 0; i < n; i++) {
const float *xx = trainset + i * d;
float * res = residuals_2 + i * d;
pq.decode (train_codes + i * pq.code_size, res);
for (int j = 0; j < d; j++)
res[j] = xx[j] - res[j];
}
delete [] train_codes;
}
if (by_residual) {
delete [] trainset;
precompute_table ();
}
}
/* produce a binary signature based on the residual vector */
void IndexIVFPQ::encode (long key, const float * x, uint8_t * code) const
{
if (by_residual) {
float residual_vec[d];
quantizer->compute_residual (x, residual_vec, key);
pq.compute_code (residual_vec, code);
}
else pq.compute_code (x, code);
}
void IndexIVFPQ::encode_multiple (size_t n, const long *keys,
const float * x, uint8_t * xcodes) const
{
if (by_residual) {
float *residuals = new float [n * d];
// TODO: parallelize?
for (size_t i = 0; i < n; i++)
quantizer->compute_residual (x + i * d, residuals + i * d, keys[i]);
pq.compute_codes (residuals, xcodes, n);
delete [] residuals;
} else {
pq.compute_codes (x, xcodes, n);
}
}
void IndexIVFPQ::add_with_ids (idx_t n, const float * x, const long *xids)
{
add_core_o (n, x, xids, nullptr);
}
void IndexIVFPQ::add_core_o (idx_t n, const float * x, const long *xids,
float *residuals_2, const long *precomputed_idx)
{
FAISS_ASSERT (is_trained);
double t0 = getmillisecs ();
const long * idx;
if (precomputed_idx) {
idx = precomputed_idx;
} else {
long * idx0 = new long [n];
quantizer->assign (n, x, idx0);
idx = idx0;
}
double t1 = getmillisecs ();
uint8_t * xcodes = new uint8_t [n * code_size];
const float *to_encode = nullptr;
if (by_residual) {
float *residuals = new float [n * d];
// TODO: parallelize?
for (size_t i = 0; i < n; i++) {
if (idx[i] < 0)
memset (residuals + i * d, 0, sizeof(*residuals) * d);
else
quantizer->compute_residual (
x + i * d, residuals + i * d, idx[i]);
}
to_encode = residuals;
} else {
to_encode = x;
}
pq.compute_codes (to_encode, xcodes, n);
double t2 = getmillisecs ();
// TODO: parallelize?
size_t n_ignore = 0;
for (size_t i = 0; i < n; i++) {
idx_t key = idx[i];
if (key < 0) {
n_ignore ++;
if (residuals_2)
memset (residuals_2, 0, sizeof(*residuals_2) * d);
continue;
}
idx_t id = xids ? xids[i] : ntotal + i;
ids[key].push_back (id);
uint8_t *code = xcodes + i * code_size;
for (size_t j = 0; j < code_size; j++)
codes[key].push_back (code[j]);
if (residuals_2) {
float *res2 = residuals_2 + i * d;
const float *xi = to_encode + i * d;
pq.decode (code, res2);
for (int j = 0; j < d; j++)
res2[j] = xi[j] - res2[j];
}
if (maintain_direct_map)
direct_map.push_back (key << 32 | (ids[key].size() - 1));
}
if (by_residual)
delete [] to_encode;
delete [] xcodes;
if (!precomputed_idx)
delete [] idx;
double t3 = getmillisecs ();
if(verbose) {
char comment[100] = {0};
if (n_ignore > 0)
snprintf (comment, 100, "(%ld vectors ignored)", n_ignore);
printf(" add_core times: %.3f %.3f %.3f %s\n",
t1 - t0, t2 - t1, t3 - t2, comment);
}
ntotal += n;
}
void IndexIVFPQ::reconstruct_n (idx_t i0, idx_t ni, float *recons) const
{
FAISS_ASSERT (ni == 0 || (i0 >= 0 && i0 + ni <= ntotal));
std::vector<float> centroid (d);
for (int key = 0; key < nlist; key++) {
const std::vector<long> & idlist = ids[key];
const uint8_t * code_line = codes[key].data();
for (long ofs = 0; ofs < idlist.size(); ofs++) {
long id = idlist[ofs];
if (!(id >= i0 && id < i0 + ni)) continue;
float *r = recons + d * (id - i0);
if (by_residual) {
quantizer->reconstruct (key, centroid.data());
pq.decode (code_line + ofs * pq.code_size, r);
for (int j = 0; j < d; j++) {
r[j] += centroid[j];
}
}
else {
pq.decode (code_line + ofs * pq.code_size, r);
}
}
}
}
void IndexIVFPQ::reconstruct (idx_t key, float * recons) const
{
FAISS_ASSERT (direct_map.size() == ntotal);
int list_no = direct_map[key] >> 32;
int ofs = direct_map[key] & 0xffffffff;
quantizer->reconstruct (list_no, recons);
const uint8_t * code = &(codes[list_no][ofs * pq.code_size]);
for (size_t m = 0; m < pq.M; m++) {
float * out = recons + m * pq.dsub;
const float * cent = pq.get_centroids (m, code[m]);
for (size_t i = 0; i < pq.dsub; i++) {
out[i] += cent[i];
}
}
}
void IndexIVFPQ::merge_from_residuals (IndexIVF &other_in)
{
IndexIVFPQ &other = dynamic_cast<IndexIVFPQ &> (other_in);
for (int i = 0; i < nlist; i++) {
codes[i].insert (codes[i].end(),
other.codes[i].begin(), other.codes[i].end());
other.codes[i].clear();
}
}
void IndexIVFPQ::copy_subset_to (IndexIVFPQ & other, int subset_type,
long a1, long a2) const
{
FAISS_ASSERT (nlist == other.nlist);
FAISS_ASSERT (!other.maintain_direct_map);
size_t code_size = pq.code_size;
for (long list_no = 0; list_no < nlist; list_no++) {
const std::vector<idx_t> & ids_in = ids[list_no];
std::vector<idx_t> & ids_out = other.ids[list_no];
const std::vector<uint8_t> & codes_in = codes[list_no];
std::vector<uint8_t> & codes_out = other.codes[list_no];
for (long i = 0; i < ids_in.size(); i++) {
idx_t id = ids_in[i];
if (subset_type == 0 && a1 <= id && id < a2) {
ids_out.push_back (id);
codes_out.insert (codes_out.end(),
codes_in.begin() + i * code_size,
codes_in.begin() + (i + 1) * code_size);
other.ntotal++;
}
}
}
}
/** Precomputed tables for residuals
*
* During IVFPQ search with by_residual, we compute
*
* d = || x - y_C - y_R ||^2
*
* where x is the query vector, y_C the coarse centroid, y_R the
* refined PQ centroid. The expression can be decomposed as:
*
* d = || x - y_C ||^2 + || y_R ||^2 + 2 * (y_C|y_R) - 2 * (x|y_R)
* --------------- --------------------------- -------
* term 1 term 2 term 3
*
* When using multiprobe, we use the following decomposition:
* - term 1 is the distance to the coarse centroid, that is computed
* during the 1st stage search.
* - term 2 can be precomputed, as it does not involve x. However,
* because of the PQ, it needs nlist * M * ksub storage. This is why
* use_precomputed_table is off by default
* - term 3 is the classical non-residual distance table.
*
* Since y_R defined by a product quantizer, it is split across
* subvectors and stored separately for each subvector. If the coarse
* quantizer is a MultiIndexQuantizer then the table can be stored
* more compactly.
*
* At search time, the tables for term 2 and term 3 are added up. This
* is faster when the length of the lists is > ksub * M.
*/
void IndexIVFPQ::precompute_table ()
{
if (use_precomputed_table == 0) { // then choose the type of table
if (quantizer->metric_type == METRIC_INNER_PRODUCT) {
fprintf(stderr, "IndexIVFPQ::precompute_table: WARN precomputed "
"tables not supported for inner product quantizers\n");
return;
}
const MultiIndexQuantizer *miq =
dynamic_cast<const MultiIndexQuantizer *> (quantizer);
if (miq && pq.M % miq->pq.M == 0)
use_precomputed_table = 2;
else
use_precomputed_table = 1;
} // otherwise assume user has set appropriate flag on input
// squared norms of the PQ centroids
std::vector<float> r_norms (pq.M * pq.ksub, 0.0/0.0);
for (int m = 0; m < pq.M; m++)
for (int j = 0; j < pq.ksub; j++)
r_norms [m * pq.ksub + j] =
fvec_norm_L2sqr (pq.get_centroids (m, j), pq.dsub);
if (use_precomputed_table == 1) {
precomputed_table.resize (nlist * pq.M * pq.ksub);
std::vector<float> centroid (d);
for (size_t i = 0; i < nlist; i++) {
quantizer->reconstruct (i, centroid.data());
float *tab = &precomputed_table[i * pq.M * pq.ksub];
pq.compute_inner_prod_table (centroid.data(), tab);
fvec_madd (pq.M * pq.ksub, r_norms.data(), 2.0, tab, tab);
}
} else if (use_precomputed_table == 2) {
const MultiIndexQuantizer *miq =
dynamic_cast<const MultiIndexQuantizer *> (quantizer);
FAISS_ASSERT (miq);
const ProductQuantizer &cpq = miq->pq;
FAISS_ASSERT (pq.M % cpq.M == 0);
precomputed_table.resize(cpq.ksub * pq.M * pq.ksub);
// reorder PQ centroid table
std::vector<float> centroids (d * cpq.ksub, 0.0/0.0);
for (int m = 0; m < cpq.M; m++) {
for (size_t i = 0; i < cpq.ksub; i++) {
memcpy (centroids.data() + i * d + m * cpq.dsub,
cpq.get_centroids (m, i),
sizeof (*centroids.data()) * cpq.dsub);
}
}
pq.compute_inner_prod_tables (cpq.ksub, centroids.data (),
precomputed_table.data ());
for (size_t i = 0; i < cpq.ksub; i++) {
float *tab = &precomputed_table[i * pq.M * pq.ksub];
fvec_madd (pq.M * pq.ksub, r_norms.data(), 2.0, tab, tab);
}
}
}
namespace {
static uint64_t get_cycles () {
uint32_t high, low;
asm volatile("rdtsc \n\t"
: "=a" (low),
"=d" (high));
return ((uint64_t)high << 32) | (low);
}
#define TIC t0 = get_cycles()
#define TOC get_cycles () - t0
/** QueryTables manages the various ways of searching an
* IndexIVFPQ. The code contains a lot of branches, depending on:
* - metric_type: are we computing L2 or Inner product similarity?
* - by_residual: do we encode raw vectors or residuals?
* - use_precomputed_table: are x_R|x_C tables precomputed?
* - polysemous_ht: are we filtering with polysemous codes?
*/
struct QueryTables {
/*****************************************************
* General data from the IVFPQ
*****************************************************/
const IndexIVFPQ & ivfpq;
// copied from IndexIVFPQ for easier access
int d;
const ProductQuantizer & pq;
MetricType metric_type;
bool by_residual;
int use_precomputed_table;
// pre-allocated data buffers
float * sim_table, * sim_table_2;
float * residual_vec, *decoded_vec;
// single data buffer
std::vector<float> mem;
// for table pointers
std::vector<const float *> sim_table_ptrs;
explicit QueryTables (const IndexIVFPQ & ivfpq):
ivfpq(ivfpq),
d(ivfpq.d),
pq (ivfpq.pq),
metric_type (ivfpq.metric_type),
by_residual (ivfpq.by_residual),
use_precomputed_table (ivfpq.use_precomputed_table)
{
mem.resize (pq.ksub * pq.M * 2 + d *2);
sim_table = mem.data();
sim_table_2 = sim_table + pq.ksub * pq.M;
residual_vec = sim_table_2 + pq.ksub * pq.M;
decoded_vec = residual_vec + d;
// for polysemous
if (ivfpq.polysemous_ht != 0) {
q_code.resize (pq.code_size);
}
init_list_cycles = 0;
sim_table_ptrs.resize (pq.M);
}
/*****************************************************
* What we do when query is known
*****************************************************/
// field specific to query
const float * qi;
// query-specific intialization
void init_query (const float * qi) {
this->qi = qi;
if (metric_type == METRIC_INNER_PRODUCT)
init_query_IP ();
else
init_query_L2 ();
if (!by_residual && ivfpq.polysemous_ht != 0)
pq.compute_code (qi, q_code.data());
}
void init_query_IP () {
// precompute some tables specific to the query qi
pq.compute_inner_prod_table (qi, sim_table);
// we compute negated inner products for use with the maxheap
for (int i = 0; i < pq.ksub * pq.M; i++) {
sim_table[i] = - sim_table[i];
}
}
void init_query_L2 () {
if (!by_residual) {
pq.compute_distance_table (qi, sim_table);
} else if (use_precomputed_table) {
pq.compute_inner_prod_table (qi, sim_table_2);
}
}
/*****************************************************
* When inverted list is known: prepare computations
*****************************************************/
// fields specific to list
Index::idx_t key;
float coarse_dis;
std::vector<uint8_t> q_code;
uint64_t init_list_cycles;
/// once we know the query and the centroid, we can prepare the
/// sim_table that will be used for accumulation
/// and dis0, the initial value
float precompute_list_tables () {
float dis0 = 0;
uint64_t t0; TIC;
if (by_residual) {
if (metric_type == METRIC_INNER_PRODUCT)
dis0 = precompute_list_tables_IP ();
else
dis0 = precompute_list_tables_L2 ();
}
init_list_cycles += TOC;
return dis0;
}
float precompute_list_table_pointers () {
float dis0 = 0;
uint64_t t0; TIC;
if (by_residual) {
if (metric_type == METRIC_INNER_PRODUCT)
FAISS_ASSERT (!"not implemented");
else
dis0 = precompute_list_table_pointers_L2 ();
}
init_list_cycles += TOC;
return dis0;
}
/*****************************************************
* compute tables for inner prod
*****************************************************/
float precompute_list_tables_IP ()
{
// prepare the sim_table that will be used for accumulation
// and dis0, the initial value
ivfpq.quantizer->reconstruct (key, decoded_vec);
// decoded_vec = centroid
float dis0 = -fvec_inner_product (qi, decoded_vec, d);
if (ivfpq.polysemous_ht) {
for (int i = 0; i < d; i++) {
residual_vec [i] = qi[i] - decoded_vec[i];
}
pq.compute_code (residual_vec, q_code.data());
}
return dis0;
}
/*****************************************************
* compute tables for L2 distance
*****************************************************/
float precompute_list_tables_L2 ()
{
float dis0 = 0;
if (use_precomputed_table == 0) {
ivfpq.quantizer->compute_residual (qi, residual_vec, key);
pq.compute_distance_table (residual_vec, sim_table);
} else if (use_precomputed_table == 1) {
dis0 = coarse_dis;
fvec_madd (pq.M * pq.ksub,
&ivfpq.precomputed_table [key * pq.ksub * pq.M],
-2.0, sim_table_2,
sim_table);
} else if (use_precomputed_table == 2) {
dis0 = coarse_dis;
const MultiIndexQuantizer *miq =
dynamic_cast<const MultiIndexQuantizer *> (ivfpq.quantizer);
FAISS_ASSERT (miq);
const ProductQuantizer &cpq = miq->pq;
int Mf = pq.M / cpq.M;
const float *qtab = sim_table_2; // query-specific table
float *ltab = sim_table; // (output) list-specific table
long k = key;
for (int cm = 0; cm < cpq.M; cm++) {
// compute PQ index
int ki = k & ((uint64_t(1) << cpq.nbits) - 1);
k >>= cpq.nbits;
// get corresponding table
const float *pc = &ivfpq.precomputed_table
[(ki * pq.M + cm * Mf) * pq.ksub];
if (ivfpq.polysemous_ht == 0) {
// sum up with query-specific table
fvec_madd (Mf * pq.ksub,
pc,
-2.0, qtab,
ltab);
ltab += Mf * pq.ksub;
qtab += Mf * pq.ksub;
} else {
for (int m = cm * Mf; m < (cm + 1) * Mf; m++) {
q_code[m] = fvec_madd_and_argmin
(pq.ksub, pc, -2, qtab, ltab);
pc += pq.ksub;
ltab += pq.ksub;
qtab += pq.ksub;
}
}
}
}
return dis0;
}
float precompute_list_table_pointers_L2 ()
{
float dis0 = 0;
if (use_precomputed_table == 1) {
dis0 = coarse_dis;
const float * s = &ivfpq.precomputed_table [key * pq.ksub * pq.M];
for (int m = 0; m < pq.M; m++) {
sim_table_ptrs [m] = s;
s += pq.ksub;
}
} else if (use_precomputed_table == 2) {
dis0 = coarse_dis;
const MultiIndexQuantizer *miq =
dynamic_cast<const MultiIndexQuantizer *> (ivfpq.quantizer);
FAISS_ASSERT (miq);
const ProductQuantizer &cpq = miq->pq;
int Mf = pq.M / cpq.M;
long k = key;
int m0 = 0;
for (int cm = 0; cm < cpq.M; cm++) {
int ki = k & ((uint64_t(1) << cpq.nbits) - 1);
k >>= cpq.nbits;
const float *pc = &ivfpq.precomputed_table
[(ki * pq.M + cm * Mf) * pq.ksub];
for (int m = m0; m < m0 + Mf; m++) {
sim_table_ptrs [m] = pc;
pc += pq.ksub;
}
m0 += Mf;
}
} else FAISS_ASSERT (!"need precomputed tables");
if (ivfpq.polysemous_ht) {
FAISS_ASSERT (!"not implemented");
// Not clear that it makes sense to implemente this,
// because it costs M * ksub, which is what we wanted to
// avoid with the tables pointers.
}
return dis0;
}
};
/*****************************************************
* Scaning the codes.
* The scanning functions call their favorite precompute_*
* function to precompute the tables they need.
*****************************************************/
template <typename IDType>
struct InvertedListScanner: QueryTables {
const uint8_t * __restrict list_codes;
const IDType * list_ids;
size_t list_size;
explicit InvertedListScanner (const IndexIVFPQ & ivfpq):
QueryTables (ivfpq)
{
FAISS_ASSERT(pq.byte_per_idx == 1);
n_hamming_pass = 0;
}
/// list_specific intialization
void init_list (Index::idx_t key, float coarse_dis,
size_t list_size_in, const IDType *list_ids_in,
const uint8_t *list_codes_in) {
this->key = key;
this->coarse_dis = coarse_dis;
list_size = list_size_in;
list_codes = list_codes_in;
list_ids = list_ids_in;
}
/*****************************************************
* Scaning the codes: simple PQ scan.
*****************************************************/
/// version of the scan where we use precomputed tables
void scan_list_with_table (
size_t k, float * heap_sim, long * heap_ids, bool store_pairs)
{
float dis0 = precompute_list_tables ();
for (size_t j = 0; j < list_size; j++) {
float dis = dis0;
const float *tab = sim_table;
for (size_t m = 0; m < pq.M; m++) {
dis += tab[*list_codes++];
tab += pq.ksub;
}
if (dis < heap_sim[0]) {
maxheap_pop (k, heap_sim, heap_ids);
long id = store_pairs ? (key << 32 | j) : list_ids[j];
maxheap_push (k, heap_sim, heap_ids, dis, id);
}
}
}
/// tables are not precomputed, but pointers are provided to the
/// relevant X_c|x_r tables
void scan_list_with_pointer (
size_t k, float * heap_sim, long * heap_ids, bool store_pairs)
{
float dis0 = precompute_list_table_pointers ();
for (size_t j = 0; j < list_size; j++) {
float dis = dis0;
const float *tab = sim_table_2;
for (size_t m = 0; m < pq.M; m++) {
int ci = *list_codes++;
dis += sim_table_ptrs [m][ci] - 2 * tab [ci];
tab += pq.ksub;
}
if (dis < heap_sim[0]) {
maxheap_pop (k, heap_sim, heap_ids);
long id = store_pairs ? (key << 32 | j) : list_ids[j];
maxheap_push (k, heap_sim, heap_ids, dis, id);
}
}
}
/// nothing is precomputed: access residuals on-the-fly
void scan_on_the_fly_dist (
size_t k, float * heap_sim, long * heap_ids, bool store_pairs)
{
if (by_residual && use_precomputed_table) {
scan_list_with_pointer (k, heap_sim, heap_ids, store_pairs);
return;
}
const float *dvec;
float dis0 = 0;
if (by_residual) {
if (metric_type == METRIC_INNER_PRODUCT) {
ivfpq.quantizer->reconstruct (key, residual_vec);
dis0 = fvec_inner_product (residual_vec, qi, d);
} else {
ivfpq.quantizer->compute_residual (qi, residual_vec, key);
}
dvec = residual_vec;
} else {
dvec = qi;
dis0 = 0;
}
for (size_t j = 0; j < list_size; j++) {
pq.decode (list_codes, decoded_vec);
list_codes += pq.code_size;
float dis;
if (metric_type == METRIC_INNER_PRODUCT) {
dis = -dis0 - fvec_inner_product (decoded_vec, qi, d);
} else {
dis = fvec_L2sqr (decoded_vec, dvec, d);
}
if (dis < heap_sim[0]) {
maxheap_pop (k, heap_sim, heap_ids);
long id = store_pairs ? (key << 32 | j) : list_ids[j];
maxheap_push (k, heap_sim, heap_ids, dis, id);
}
}
}
/*****************************************************
* Scanning codes with polysemous filtering
*****************************************************/
// code for the query
size_t n_hamming_pass;
template <class HammingComputer>
void scan_list_polysemous_hc (
size_t k, float * heap_sim, long * heap_ids, bool store_pairs)
{
float dis0 = precompute_list_tables ();
int ht = ivfpq.polysemous_ht;
int code_size = pq.code_size;
HammingComputer hc (q_code.data(), code_size);
for (size_t j = 0; j < list_size; j++) {
const uint8_t *b_code = list_codes;
int hd = hc.hamming (b_code);
if (hd < ht) {
n_hamming_pass ++;
float dis = dis0;
const float *tab = sim_table;
for (size_t m = 0; m < pq.M; m++) {
dis += tab[*b_code++];
tab += pq.ksub;
}
if (dis < heap_sim[0]) {
maxheap_pop (k, heap_sim, heap_ids);
long id = store_pairs ? (key << 32 | j) : list_ids[j];
maxheap_push (k, heap_sim, heap_ids, dis, id);
}
}
list_codes += code_size;
}
}
void scan_list_polysemous (
size_t k, float * heap_sim, long * heap_ids, bool store_pairs)
{
switch (pq.code_size) {
#define HANDLE_CODE_SIZE(cs) \
case cs: \
scan_list_polysemous_hc <HammingComputer ## cs> \
(k, heap_sim, heap_ids, store_pairs); \
break
HANDLE_CODE_SIZE(4);
HANDLE_CODE_SIZE(8);
HANDLE_CODE_SIZE(16);
HANDLE_CODE_SIZE(20);
HANDLE_CODE_SIZE(32);
HANDLE_CODE_SIZE(64);
#undef HANDLE_CODE_SIZE
default:
if (pq.code_size % 8 == 0)
scan_list_polysemous_hc <HammingComputerM8>
(k, heap_sim, heap_ids, store_pairs);
else
scan_list_polysemous_hc <HammingComputerM4>
(k, heap_sim, heap_ids, store_pairs);
break;
}
}
};
} // anonymous namespace
IndexIVFPQStats indexIVFPQ_stats;
void IndexIVFPQStats::reset () {
memset (this, 0, sizeof (*this));
}
void IndexIVFPQ::search_knn_with_key (
size_t nx,
const float * qx,
const long * keys,
const float * coarse_dis,
float_maxheap_array_t * res,
bool store_pairs) const
{
const size_t k = res->k;
#pragma omp parallel
{
InvertedListScanner<long> qt (*this);
size_t stats_nlist = 0;
size_t stats_ncode = 0;
uint64_t init_query_cycles = 0;
uint64_t scan_cycles = 0;
uint64_t heap_cycles = 0;
#pragma omp for
for (size_t i = 0; i < nx; i++) {
const float *qi = qx + i * d;
const long * keysi = keys + i * nprobe;
const float *coarse_dis_i = coarse_dis + i * nprobe;
float * heap_sim = res->get_val (i);
long * heap_ids = res->get_ids (i);
uint64_t t0;
TIC;
maxheap_heapify (k, heap_sim, heap_ids);
heap_cycles += TOC;
TIC;
qt.init_query (qi);
init_query_cycles += TOC;
size_t nscan = 0;
for (size_t ik = 0; ik < nprobe; ik++) {
long key = keysi[ik]; /* select the list */
if (key < 0) {
// not enough centroids for multiprobe
continue;
}
if (key >= (long) nlist) {
fprintf (stderr, "Invalid key=%ld nlist=%ld\n", key, nlist);
throw;
}
size_t list_size = ids[key].size();
stats_nlist ++;
nscan += list_size;
if (list_size == 0) continue;
qt.init_list (key, coarse_dis_i[ik],
list_size, ids[key].data(),
codes[key].data());
TIC;
if (polysemous_ht > 0) {
qt.scan_list_polysemous
(k, heap_sim, heap_ids, store_pairs);
} else if (list_size > scan_table_threshold) {
qt.scan_list_with_table (k, heap_sim, heap_ids, store_pairs);
} else {
qt.scan_on_the_fly_dist (k, heap_sim, heap_ids, store_pairs);
}
scan_cycles += TOC;
if (max_codes && nscan >= max_codes) break;
}
stats_ncode += nscan;
TIC;
maxheap_reorder (k, heap_sim, heap_ids);
if (metric_type == METRIC_INNER_PRODUCT) {
for (size_t j = 0; j < k; j++)
heap_sim[j] = -heap_sim[j];
}
heap_cycles += TOC;
}
#pragma omp critical
{
indexIVFPQ_stats.n_hamming_pass += qt.n_hamming_pass;
indexIVFPQ_stats.nlist += stats_nlist;
indexIVFPQ_stats.ncode += stats_ncode;
indexIVFPQ_stats.init_query_cycles += init_query_cycles;
indexIVFPQ_stats.init_list_cycles += qt.init_list_cycles;
indexIVFPQ_stats.scan_cycles += scan_cycles - qt.init_list_cycles;
indexIVFPQ_stats.heap_cycles += heap_cycles;
}
}
indexIVFPQ_stats.nq += nx;
}
void IndexIVFPQ::search (idx_t n, const float *x, idx_t k,
float *distances, idx_t *labels) const
{
long * idx = new long [n * nprobe];
float * coarse_dis = new float [n * nprobe];
uint64_t t0;
TIC;
quantizer->search (n, x, nprobe, coarse_dis, idx);
indexIVFPQ_stats.assign_cycles += TOC;
TIC;
float_maxheap_array_t res = { size_t(n), size_t(k), labels, distances};
search_knn_with_key (n, x, idx, coarse_dis, &res);
delete [] idx;
delete [] coarse_dis;
indexIVFPQ_stats.search_cycles += TOC;
}
void IndexIVFPQ::reset()
{
IndexIVF::reset();
for (size_t key = 0; key < nlist; key++) {
codes[key].clear();
}
}
long IndexIVFPQ::remove_ids (const IDSelector & sel)
{
FAISS_ASSERT (!maintain_direct_map ||
!"direct map remove not implemented");
long nremove = 0;
#pragma omp parallel for reduction(+: nremove)
for (long i = 0; i < nlist; i++) {
std::vector<idx_t> & idsi = ids[i];
uint8_t * codesi = codes[i].data();
long l = idsi.size(), j = 0;
while (j < l) {
if (sel.is_member (idsi[j])) {
l--;
idsi [j] = idsi [l];
memmove (codesi + j * code_size,
codesi + l * code_size, code_size);
} else {
j++;
}
}
if (l < idsi.size()) {
nremove += idsi.size() - l;
idsi.resize (l);
codes[i].resize (l * code_size);
}
}
ntotal -= nremove;
return nremove;
}
IndexIVFPQ::IndexIVFPQ ()
{
// initialize some runtime values
use_precomputed_table = 0;
scan_table_threshold = 0;
do_polysemous_training = false;
polysemous_ht = 0;
max_codes = 0;
polysemous_training = nullptr;
}
struct CodeCmp {
const uint8_t *tab;
size_t code_size;
bool operator () (int a, int b) const {
return cmp (a, b) > 0;
}
int cmp (int a, int b) const {
return memcmp (tab + a * code_size, tab + b * code_size,
code_size);
}
};
size_t IndexIVFPQ::find_duplicates (idx_t *dup_ids, size_t *lims) const
{
size_t ngroup = 0;
lims[0] = 0;
for (size_t list_no = 0; list_no < nlist; list_no++) {
size_t n = ids[list_no].size();
std::vector<int> ord (n);
for (int i = 0; i < n; i++) ord[i] = i;
CodeCmp cs = { codes[list_no].data(), code_size };
std::sort (ord.begin(), ord.end(), cs);
const idx_t *list_ids = ids[list_no].data();
int prev = -1; // all elements from prev to i-1 are equal
for (int i = 0; i < n; i++) {
if (prev >= 0 && cs.cmp (ord [prev], ord [i]) == 0) {
// same as previous => remember
if (prev + 1 == i) { // start new group
ngroup++;
lims[ngroup] = lims[ngroup - 1];
dup_ids [lims [ngroup]++] = list_ids [ord [prev]];
}
dup_ids [lims [ngroup]++] = list_ids [ord [i]];
} else { // not same as previous.
prev = i;
}
}
}
return ngroup;
}
/*****************************************
* IndexIVFPQR implementation
******************************************/
IndexIVFPQR::IndexIVFPQR (
Index * quantizer, size_t d, size_t nlist,
size_t M, size_t nbits_per_idx,
size_t M_refine, size_t nbits_per_idx_refine):
IndexIVFPQ (quantizer, d, nlist, M, nbits_per_idx),
refine_pq (d, M_refine, nbits_per_idx_refine),
k_factor (4)
{
by_residual = true;
set_typename();
}
IndexIVFPQR::IndexIVFPQR ():
k_factor (1)
{
by_residual = true;
}
void IndexIVFPQR::set_typename()
{
std::stringstream s;
s << "IvfPQR_" << pq.M << "x" << pq.nbits
<< "+" << refine_pq.M << "x" << refine_pq.nbits
<< "[" << nlist << ":" << quantizer->index_typename << "]";
index_typename = s.str();
}
void IndexIVFPQR::reset()
{
IndexIVFPQ::reset();
refine_codes.clear();
}
void IndexIVFPQR::train_residual (idx_t n, const float *x)
{
float * residual_2 = new float [n * d];
train_residual_o (n, x, residual_2);
if (verbose)
printf ("training %zdx%zd 2nd level PQ quantizer on %ld %dD-vectors\n",
refine_pq.M, refine_pq.ksub, n, d);
refine_pq.cp.max_points_per_centroid = 1000;
refine_pq.cp.verbose = verbose;
refine_pq.train (n, residual_2);
delete [] residual_2;
}
void IndexIVFPQR::add_with_ids (idx_t n, const float *x, const long *xids) {
add_core (n, x, xids, nullptr);
}
void IndexIVFPQR::add_core (idx_t n, const float *x, const long *xids,
const long *precomputed_idx) {
float * residual_2 = new float [n * d];
idx_t n0 = ntotal;
add_core_o (n, x, xids, residual_2, precomputed_idx);
refine_codes.resize (ntotal * refine_pq.code_size);
refine_pq.compute_codes (
residual_2, &refine_codes[n0 * refine_pq.code_size], n);
delete [] residual_2;
}
void IndexIVFPQR::search (
idx_t n, const float *x, idx_t k,
float *distances, idx_t *labels) const
{
FAISS_ASSERT (is_trained);
long * idx = new long [n * nprobe];
float * L1_dis = new float [n * nprobe];
uint64_t t0;
TIC;
quantizer->search (n, x, nprobe, L1_dis, idx);
indexIVFPQ_stats.assign_cycles += TOC;
TIC;
size_t k_coarse = long(k * k_factor);
idx_t *coarse_labels = new idx_t [k_coarse * n];
{ // query with quantizer levels 1 and 2.
float *coarse_distances = new float [k_coarse * n];
faiss::float_maxheap_array_t res_coarse = {
size_t(n), k_coarse, coarse_labels, coarse_distances};
search_knn_with_key (n, x, idx, L1_dis, &res_coarse, true);
delete [] coarse_distances;
}
delete [] L1_dis;
indexIVFPQ_stats.search_cycles += TOC;
TIC;
// 3rd level refinement
size_t n_refine = 0;
#pragma omp parallel reduction(+ : n_refine)
{
// tmp buffers
float *residual_1 = new float [2 * d];
float *residual_2 = residual_1 + d;
#pragma omp for
for (idx_t i = 0; i < n; i++) {
const float *xq = x + i * d;
const long * shortlist = coarse_labels + k_coarse * i;
float * heap_sim = distances + k * i;
long * heap_ids = labels + k * i;
maxheap_heapify (k, heap_sim, heap_ids);
for (int j = 0; j < k_coarse; j++) {
long sl = shortlist[j];
if (sl == -1) continue;
int list_no = sl >> 32;
int ofs = sl & 0xffffffff;
assert (list_no >= 0 && list_no < nlist);
assert (ofs >= 0 && ofs < ids[list_no].size());
// 1st level residual
quantizer->compute_residual (xq, residual_1, list_no);
// 2nd level residual
const uint8_t * l2code = &codes[list_no][ofs * pq.code_size];
pq.decode (l2code, residual_2);
for (int l = 0; l < d; l++)
residual_2[l] = residual_1[l] - residual_2[l];
// 3rd level residual's approximation
idx_t id = ids[list_no][ofs];
assert (0 <= id && id < ntotal);
refine_pq.decode (&refine_codes [id * refine_pq.code_size],
residual_1);
float dis = fvec_L2sqr (residual_1, residual_2, d);
if (dis < heap_sim[0]) {
maxheap_pop (k, heap_sim, heap_ids);
maxheap_push (k, heap_sim, heap_ids, dis, id);
}
n_refine ++;
}
maxheap_reorder (k, heap_sim, heap_ids);
}
delete [] residual_1;
}
delete [] coarse_labels;
delete [] idx;
indexIVFPQ_stats.nrefine += n_refine;
indexIVFPQ_stats.refine_cycles += TOC;
}
void IndexIVFPQR::reconstruct_n (idx_t i0, idx_t ni, float *recons) const
{
float *r3 = new float [d];
IndexIVFPQ::reconstruct_n (i0, ni, recons);
for (idx_t i = i0; i < i0 + ni; i++) {
float *r = recons + i * d;
refine_pq.decode (&refine_codes [i * refine_pq.code_size], r3);
for (int j = 0; j < d; j++)
r[j] += r3[j];
}
delete [] r3;
}
void IndexIVFPQR::merge_from_residuals (IndexIVF &other_in)
{
IndexIVFPQR &other = dynamic_cast<IndexIVFPQR &> (other_in);
IndexIVFPQ::merge_from_residuals (other);
refine_codes.insert (refine_codes.end(),
other.refine_codes.begin(), other.refine_codes.end());
other.refine_codes.clear();
}
long IndexIVFPQR::remove_ids (const IDSelector & sel)
{
FAISS_ASSERT(!"not implemented");
}
/*****************************************
* IndexIVFPQCompact implementation
******************************************/
IndexIVFPQCompact::IndexIVFPQCompact ()
{
alloc_type = Alloc_type_none;
limits = nullptr;
compact_ids = nullptr;
compact_codes = nullptr;
}
IndexIVFPQCompact::IndexIVFPQCompact (const IndexIVFPQ &other)
{
FAISS_ASSERT (other.ntotal < (1UL << 31) ||
!"IndexIVFPQCompact cannot store more than 2G images");
// here it would be more convenient to just use the
// copy-constructor, but it would copy the lists as well: too much
// overhead...
// copy fields from Index
d = other.d;
ntotal = other.ntotal;
verbose = other.verbose;
is_trained = other.is_trained;
metric_type = other.metric_type;
// copy fields from IndexIVF (except ids)
nlist = other.nlist;
nprobe = other.nprobe;
quantizer = other.quantizer;
quantizer_trains_alone = other.quantizer_trains_alone;
own_fields = false;
direct_map = other.direct_map;
// copy fields from IndexIVFPQ (except codes)
by_residual = other.by_residual;
use_precomputed_table = other.use_precomputed_table;
precomputed_table = other.precomputed_table;
code_size = other.code_size;
pq = other.pq;
do_polysemous_training = other.do_polysemous_training;
polysemous_training = nullptr;
scan_table_threshold = other.scan_table_threshold;
max_codes = other.max_codes;
polysemous_ht = other.polysemous_ht;
//allocate
alloc_type = Alloc_type_new;
limits = new uint32_t [nlist + 1];
compact_ids = new uint32_t [ntotal];
compact_codes = new uint8_t [ntotal * code_size];
// copy content from other
size_t ofs = 0;
for (size_t i = 0; i < nlist; i++) {
limits [i] = ofs;
const std::vector<long> &other_ids = other.ids[i];
for (size_t j = 0; j < other_ids.size(); j++) {
long id = other_ids[j];
FAISS_ASSERT (id < (1UL << 31) ||
!"IndexIVFPQCompact cannot store ids > 2G");
compact_ids[ofs + j] = id;
}
memcpy (compact_codes + ofs * code_size,
other.codes[i].data(),
other.codes[i].size());
ofs += other_ids.size();
}
FAISS_ASSERT (ofs == ntotal);
limits [nlist] = ofs;
}
void IndexIVFPQCompact::add (idx_t, const float *) {
FAISS_ASSERT (!"cannot add to an IndexIVFPQCompact");
}
void IndexIVFPQCompact::reset () {
FAISS_ASSERT (!"cannot reset an IndexIVFPQCompact");
}
void IndexIVFPQCompact::train (idx_t, const float *) {
FAISS_ASSERT (!"cannot train an IndexIVFPQCompact");
}
IndexIVFPQCompact::~IndexIVFPQCompact ()
{
if (alloc_type == Alloc_type_new) {
delete [] limits;
delete [] compact_codes;
delete [] compact_ids;
} else if (alloc_type == Alloc_type_mmap) {
munmap (mmap_buffer, mmap_length);
}
}
void IndexIVFPQCompact::search_knn_with_key (
size_t nx,
const float * qx,
const long * keys,
const float * coarse_dis,
float_maxheap_array_t * res,
bool store_pairs) const
{
const size_t k = res->k;
#pragma omp parallel
{
InvertedListScanner<uint32_t> qt (*this);
size_t stats_nlist = 0;
size_t stats_ncode = 0;
uint64_t init_query_cycles = 0;
uint64_t scan_cycles = 0;
uint64_t heap_cycles = 0;
#pragma omp for
for (size_t i = 0; i < nx; i++) {
const float *qi = qx + i * d;
const long * keysi = keys + i * nprobe;
const float *coarse_dis_i = coarse_dis + i * nprobe;
float * heap_sim = res->get_val (i);
long * heap_ids = res->get_ids (i);
uint64_t t0;
TIC;
maxheap_heapify (k, heap_sim, heap_ids);
heap_cycles += TOC;
TIC;
qt.init_query (qi);
init_query_cycles += TOC;
size_t nscan = 0;
for (size_t ik = 0; ik < nprobe; ik++) {
long key = keysi[ik]; /* select the list */
if (key < 0) {
// not enough centroids for multiprobe
continue;
}
if (key >= (long) nlist) {
fprintf (stderr, "Invalid key=%ld nlist=%ld\n", key, nlist);
throw;
}
size_t list_size = limits[key + 1] - limits[key];
stats_nlist ++;
nscan += list_size;
if (list_size == 0) continue;
qt.init_list (key, coarse_dis_i[ik],
list_size, compact_ids + limits[key],
compact_codes + limits[key] * code_size);
TIC;
if (polysemous_ht > 0) {
qt.scan_list_polysemous
(k, heap_sim, heap_ids, store_pairs);
} else if (list_size > scan_table_threshold) {
qt.scan_list_with_table (k, heap_sim, heap_ids, store_pairs);
} else {
qt.scan_on_the_fly_dist (k, heap_sim, heap_ids, store_pairs);
}
scan_cycles += TOC;
if (max_codes && nscan >= max_codes) break;
}
stats_ncode += nscan;
TIC;
maxheap_reorder (k, heap_sim, heap_ids);
if (metric_type == METRIC_INNER_PRODUCT) {
for (size_t j = 0; j < k; j++) {
heap_sim[i] = -heap_sim[i];
}
}
heap_cycles += TOC;
}
#pragma omp critical
{
indexIVFPQ_stats.n_hamming_pass += qt.n_hamming_pass;
indexIVFPQ_stats.nlist += stats_nlist;
indexIVFPQ_stats.ncode += stats_ncode;
indexIVFPQ_stats.init_query_cycles += init_query_cycles;
indexIVFPQ_stats.init_list_cycles += qt.init_list_cycles;
indexIVFPQ_stats.scan_cycles += scan_cycles - qt.init_list_cycles;
indexIVFPQ_stats.heap_cycles += heap_cycles;
}
}
indexIVFPQ_stats.nq += nx;
}
} // namespace faiss
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