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borg/src/borg/_hashindex.c

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#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#if defined (__SVR4) && defined (__sun)
#include <sys/isa_defs.h>
#endif
#if (defined(BYTE_ORDER) && (BYTE_ORDER == BIG_ENDIAN)) || \
(defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)) || \
(defined(_BIG_ENDIAN) && defined(__SVR4)&&defined(__sun))
#define BORG_BIG_ENDIAN 1
#elif (defined(BYTE_ORDER) && (BYTE_ORDER == LITTLE_ENDIAN)) || \
(defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)) || \
(defined(_LITTLE_ENDIAN) && defined(__SVR4)&&defined(__sun))
#define BORG_BIG_ENDIAN 0
#else
#error Unknown byte order
#endif
#if BORG_BIG_ENDIAN
#define _le32toh(x) __builtin_bswap32(x)
#define _htole32(x) __builtin_bswap32(x)
#else
#define _le32toh(x) (x)
#define _htole32(x) (x)
#endif
#define MAGIC "BORG_IDX"
#define MAGIC_LEN 8
typedef struct {
char magic[MAGIC_LEN];
int32_t num_entries;
int32_t num_buckets;
int8_t key_size;
int8_t value_size;
} __attribute__((__packed__)) HashHeader;
typedef struct {
void *buckets;
int num_entries;
int num_buckets;
int num_empty;
int key_size;
int value_size;
off_t bucket_size;
int lower_limit;
int upper_limit;
int min_empty;
#ifdef Py_PYTHON_H
/* buckets may be backed by a Python buffer. If buckets_buffer.buf is NULL then this is not used. */
Py_buffer buckets_buffer;
#endif
} HashIndex;
/* prime (or w/ big prime factors) hash table sizes
* not sure we need primes for borg's usage (as we have a hash function based
* on sha256, we can assume an even, seemingly random distribution of values),
* but OTOH primes don't harm.
* also, growth of the sizes starts with fast-growing 2x steps, but slows down
* more and more down to 1.1x. this is to avoid huge jumps in memory allocation,
* like e.g. 4G -> 8G.
* these values are generated by hash_sizes.py.
*/
static int hash_sizes[] = {
1031, 2053, 4099, 8209, 16411, 32771, 65537, 131101, 262147, 445649,
757607, 1287917, 2189459, 3065243, 4291319, 6007867, 8410991,
11775359, 16485527, 23079703, 27695653, 33234787, 39881729, 47858071,
57429683, 68915617, 82698751, 99238507, 119086189, 144378011, 157223263,
173476439, 190253911, 209915011, 230493629, 253169431, 278728861,
306647623, 337318939, 370742809, 408229973, 449387209, 493428073,
543105119, 596976533, 657794869, 722676499, 795815791, 874066969,
962279771, 1057701643, 1164002657, 1280003147, 1407800297, 1548442699,
1703765389, 1873768367, 2062383853, /* 32bit int ends about here */
};
#define HASH_MIN_LOAD .25
#define HASH_MAX_LOAD .75 /* don't go higher than 0.75, otherwise performance severely suffers! */
#define HASH_MAX_EFF_LOAD .93
#define MAX(x, y) ((x) > (y) ? (x): (y))
#define NELEMS(x) (sizeof(x) / sizeof((x)[0]))
#define EMPTY _htole32(0xffffffff)
#define DELETED _htole32(0xfffffffe)
#define BUCKET_ADDR(index, idx) (index->buckets + (idx * index->bucket_size))
#define BUCKET_MATCHES_KEY(index, idx, key) (memcmp(key, BUCKET_ADDR(index, idx), index->key_size) == 0)
#define BUCKET_IS_DELETED(index, idx) (*((uint32_t *)(BUCKET_ADDR(index, idx) + index->key_size)) == DELETED)
#define BUCKET_IS_EMPTY(index, idx) (*((uint32_t *)(BUCKET_ADDR(index, idx) + index->key_size)) == EMPTY)
#define BUCKET_MARK_DELETED(index, idx) (*((uint32_t *)(BUCKET_ADDR(index, idx) + index->key_size)) = DELETED)
#define BUCKET_MARK_EMPTY(index, idx) (*((uint32_t *)(BUCKET_ADDR(index, idx) + index->key_size)) = EMPTY)
#define EPRINTF_MSG(msg, ...) fprintf(stderr, "hashindex: " msg "\n", ##__VA_ARGS__)
#define EPRINTF_MSG_PATH(path, msg, ...) fprintf(stderr, "hashindex: %s: " msg "\n", path, ##__VA_ARGS__)
#define EPRINTF(msg, ...) fprintf(stderr, "hashindex: " msg "(%s)\n", ##__VA_ARGS__, strerror(errno))
#define EPRINTF_PATH(path, msg, ...) fprintf(stderr, "hashindex: %s: " msg " (%s)\n", path, ##__VA_ARGS__, strerror(errno))
#ifdef Py_PYTHON_H
static HashIndex *hashindex_read(PyObject *file_py);
static void hashindex_write(HashIndex *index, PyObject *file_py);
#endif
static HashIndex *hashindex_init(int capacity, int key_size, int value_size);
static const void *hashindex_get(HashIndex *index, const void *key);
static int hashindex_set(HashIndex *index, const void *key, const void *value);
static int hashindex_delete(HashIndex *index, const void *key);
static void *hashindex_next_key(HashIndex *index, const void *key);
/* Private API */
static void hashindex_free(HashIndex *index);
static void
hashindex_free_buckets(HashIndex *index)
{
#ifdef Py_PYTHON_H
if(index->buckets_buffer.buf) {
PyBuffer_Release(&index->buckets_buffer);
} else
#endif
{
free(index->buckets);
}
}
static int
hashindex_index(HashIndex *index, const void *key)
{
return _le32toh(*((uint32_t *)key)) % index->num_buckets;
}
static int
hashindex_lookup(HashIndex *index, const void *key, int *start_idx)
{
int didx = -1;
int start = hashindex_index(index, key);
int idx = start;
for(;;) {
if(BUCKET_IS_EMPTY(index, idx))
{
break;
}
if(BUCKET_IS_DELETED(index, idx)) {
if(didx == -1) {
didx = idx;
}
}
else if(BUCKET_MATCHES_KEY(index, idx, key)) {
if (didx != -1) {
memcpy(BUCKET_ADDR(index, didx), BUCKET_ADDR(index, idx), index->bucket_size);
BUCKET_MARK_DELETED(index, idx);
idx = didx;
}
return idx;
}
idx = (idx + 1) % index->num_buckets;
if(idx == start) {
break;
}
}
if (start_idx != NULL) {
(*start_idx) = (didx == -1) ? idx : didx;
}
return -1;
}
static int
hashindex_resize(HashIndex *index, int capacity)
{
HashIndex *new;
void *key = NULL;
int32_t key_size = index->key_size;
if(!(new = hashindex_init(capacity, key_size, index->value_size))) {
return 0;
}
while((key = hashindex_next_key(index, key))) {
if(!hashindex_set(new, key, key + key_size)) {
/* This can only happen if there's a bug in the code calculating capacity */
hashindex_free(new);
return 0;
}
}
hashindex_free_buckets(index);
index->buckets = new->buckets;
index->num_buckets = new->num_buckets;
index->num_empty = index->num_buckets - index->num_entries;
index->lower_limit = new->lower_limit;
index->upper_limit = new->upper_limit;
index->min_empty = new->min_empty;
free(new);
return 1;
}
int get_lower_limit(int num_buckets){
int min_buckets = hash_sizes[0];
if (num_buckets <= min_buckets)
return 0;
return (int)(num_buckets * HASH_MIN_LOAD);
}
int get_upper_limit(int num_buckets){
int max_buckets = hash_sizes[NELEMS(hash_sizes) - 1];
if (num_buckets >= max_buckets)
return num_buckets;
return (int)(num_buckets * HASH_MAX_LOAD);
}
int get_min_empty(int num_buckets){
/* Differently from load, the effective load also considers tombstones (deleted buckets). */
return (int)(num_buckets * (1.0 - HASH_MAX_EFF_LOAD));
}
int size_idx(int size){
/* find the hash_sizes index with entry >= size */
int elems = NELEMS(hash_sizes);
int entry, i=0;
do{
entry = hash_sizes[i++];
}while((entry < size) && (i < elems));
if (i >= elems)
return elems - 1;
i--;
return i;
}
int fit_size(int current){
int i = size_idx(current);
return hash_sizes[i];
}
int grow_size(int current){
int i = size_idx(current) + 1;
int elems = NELEMS(hash_sizes);
if (i >= elems)
return hash_sizes[elems - 1];
return hash_sizes[i];
}
int shrink_size(int current){
int i = size_idx(current) - 1;
if (i < 0)
return hash_sizes[0];
return hash_sizes[i];
}
int
count_empty(HashIndex *index)
{ /* count empty (never used) buckets. this does NOT include deleted buckets (tombstones).
* TODO: if we ever change HashHeader, save the count there so we do not need this function.
*/
int i, count = 0, capacity = index->num_buckets;
for(i = 0; i < capacity; i++) {
if(BUCKET_IS_EMPTY(index, i))
count++;
}
return count;
}
/* Public API */
#ifdef Py_PYTHON_H
static HashIndex *
hashindex_read(PyObject *file_py)
{
Py_ssize_t length, buckets_length, bytes_read;
Py_buffer header_buffer;
PyObject *header_bytes, *length_object, *bucket_bytes;
HashHeader *header;
HashIndex *index = NULL;
header_bytes = PyObject_CallMethod(file_py, "read", "n", (Py_ssize_t)sizeof(HashHeader));
if(!header_bytes) {
assert(PyErr_Occurred());
goto fail;
}
bytes_read = PyBytes_Size(header_bytes);
if(PyErr_Occurred()) {
/* TypeError, not a bytes() object */
goto fail_decref_header;
}
if(bytes_read != sizeof(HashHeader)) {
/* Truncated file */
/* Note: %zd is the format for Py_ssize_t, %zu is for size_t */
PyErr_Format(PyExc_ValueError, "Could not read header (expected %zu, but read %zd bytes)",
sizeof(HashHeader), bytes_read);
goto fail_decref_header;
}
/*
* Hash the header
* If the header is corrupted this bails before doing something stupid (like allocating 3.8 TB of memory)
*/
Py_XDECREF(PyObject_CallMethod(file_py, "hash_part", "s", "HashHeader"));
if(PyErr_Occurred()) {
if(PyErr_ExceptionMatches(PyExc_AttributeError)) {
/* Be able to work with regular file objects which do not have a hash_part method. */
PyErr_Clear();
} else {
goto fail_decref_header;
}
}
/* Find length of file */
length_object = PyObject_CallMethod(file_py, "seek", "ni", (Py_ssize_t)0, SEEK_END);
if(PyErr_Occurred()) {
goto fail_decref_header;
}
length = PyNumber_AsSsize_t(length_object, PyExc_OverflowError);
Py_DECREF(length_object);
if(PyErr_Occurred()) {
/* This shouldn't generally happen; but can if seek() returns something that's not a number */
goto fail_decref_header;
}
Py_XDECREF(PyObject_CallMethod(file_py, "seek", "ni", (Py_ssize_t)sizeof(HashHeader), SEEK_SET));
if(PyErr_Occurred()) {
goto fail_decref_header;
}
/* Set up the in-memory header */
if(!(index = malloc(sizeof(HashIndex)))) {
PyErr_NoMemory();
goto fail_decref_header;
}
PyObject_GetBuffer(header_bytes, &header_buffer, PyBUF_SIMPLE);
if(PyErr_Occurred()) {
goto fail_free_index;
}
header = (HashHeader*) header_buffer.buf;
if(memcmp(header->magic, MAGIC, MAGIC_LEN)) {
PyErr_Format(PyExc_ValueError, "Unknown MAGIC in header");
goto fail_release_header_buffer;
}
buckets_length = (Py_ssize_t)_le32toh(header->num_buckets) * (header->key_size + header->value_size);
if((Py_ssize_t)length != (Py_ssize_t)sizeof(HashHeader) + buckets_length) {
PyErr_Format(PyExc_ValueError, "Incorrect file length (expected %zd, got %zd)",
sizeof(HashHeader) + buckets_length, length);
goto fail_release_header_buffer;
}
index->num_entries = _le32toh(header->num_entries);
index->num_buckets = _le32toh(header->num_buckets);
index->key_size = header->key_size;
index->value_size = header->value_size;
index->bucket_size = index->key_size + index->value_size;
index->lower_limit = get_lower_limit(index->num_buckets);
index->upper_limit = get_upper_limit(index->num_buckets);
/*
* For indices read from disk we don't malloc() the buckets ourselves,
* we have them backed by a Python bytes() object instead, and go through
* Python I/O.
*
* Note: Issuing read(buckets_length) is okay here, because buffered readers
* will issue multiple underlying reads if necessary. This supports indices
* >2 GB on Linux. We also compare lengths later.
*/
bucket_bytes = PyObject_CallMethod(file_py, "read", "n", buckets_length);
if(!bucket_bytes) {
assert(PyErr_Occurred());
goto fail_release_header_buffer;
}
bytes_read = PyBytes_Size(bucket_bytes);
if(PyErr_Occurred()) {
/* TypeError, not a bytes() object */
goto fail_decref_buckets;
}
if(bytes_read != buckets_length) {
PyErr_Format(PyExc_ValueError, "Could not read buckets (expected %zd, got %zd)", buckets_length, bytes_read);
goto fail_decref_buckets;
}
PyObject_GetBuffer(bucket_bytes, &index->buckets_buffer, PyBUF_SIMPLE);
if(PyErr_Occurred()) {
goto fail_decref_buckets;
}
index->buckets = index->buckets_buffer.buf;
index->min_empty = get_min_empty(index->num_buckets);
index->num_empty = count_empty(index);
if(index->num_empty < index->min_empty) {
/* too many tombstones here / not enough empty buckets, do a same-size rebuild */
if(!hashindex_resize(index, index->num_buckets)) {
PyErr_Format(PyExc_ValueError, "Failed to rebuild table");
goto fail_free_buckets;
}
}
/*
* Clean intermediary objects up. Note that index is only freed if an error has occurred.
* Also note that the buffer in index->buckets_buffer holds a reference to buckets_bytes.
*/
fail_free_buckets:
if(PyErr_Occurred()) {
hashindex_free_buckets(index);
}
fail_decref_buckets:
Py_DECREF(bucket_bytes);
fail_release_header_buffer:
PyBuffer_Release(&header_buffer);
fail_free_index:
if(PyErr_Occurred()) {
free(index);
index = NULL;
}
fail_decref_header:
Py_DECREF(header_bytes);
fail:
return index;
}
#endif
static HashIndex *
hashindex_init(int capacity, int key_size, int value_size)
{
HashIndex *index;
int i;
capacity = fit_size(capacity);
if(!(index = malloc(sizeof(HashIndex)))) {
EPRINTF("malloc header failed");
return NULL;
}
if(!(index->buckets = calloc(capacity, key_size + value_size))) {
EPRINTF("malloc buckets failed");
free(index);
return NULL;
}
index->num_entries = 0;
index->key_size = key_size;
index->value_size = value_size;
index->num_buckets = capacity;
index->num_empty = capacity;
index->bucket_size = index->key_size + index->value_size;
index->lower_limit = get_lower_limit(index->num_buckets);
index->upper_limit = get_upper_limit(index->num_buckets);
index->min_empty = get_min_empty(index->num_buckets);
#ifdef Py_PYTHON_H
index->buckets_buffer.buf = NULL;
#endif
for(i = 0; i < capacity; i++) {
BUCKET_MARK_EMPTY(index, i);
}
return index;
}
static void
hashindex_free(HashIndex *index)
{
hashindex_free_buckets(index);
free(index);
}
#ifdef Py_PYTHON_H
static void
hashindex_write(HashIndex *index, PyObject *file_py)
{
PyObject *length_object, *buckets_view;
Py_ssize_t length;
Py_ssize_t buckets_length = (Py_ssize_t)index->num_buckets * index->bucket_size;
HashHeader header = {
.magic = MAGIC,
.num_entries = _htole32(index->num_entries),
.num_buckets = _htole32(index->num_buckets),
.key_size = index->key_size,
.value_size = index->value_size
};
length_object = PyObject_CallMethod(file_py, "write", "y#", &header, (int)sizeof(HashHeader));
if(PyErr_Occurred()) {
return;
}
length = PyNumber_AsSsize_t(length_object, PyExc_OverflowError);
Py_DECREF(length_object);
if(PyErr_Occurred()) {
return;
}
if(length != sizeof(HashHeader)) {
PyErr_SetString(PyExc_ValueError, "Failed to write header");
return;
}
/*
* Hash the header
*/
Py_XDECREF(PyObject_CallMethod(file_py, "hash_part", "s", "HashHeader"));
if(PyErr_Occurred()) {
if(PyErr_ExceptionMatches(PyExc_AttributeError)) {
/* Be able to work with regular file objects which do not have a hash_part method. */
PyErr_Clear();
} else {
return;
}
}
/* Note: explicitly construct view; BuildValue can convert (pointer, length) to Python objects, but copies them for doing so */
buckets_view = PyMemoryView_FromMemory((char*)index->buckets, buckets_length, PyBUF_READ);
if(!buckets_view) {
assert(PyErr_Occurred());
return;
}
length_object = PyObject_CallMethod(file_py, "write", "O", buckets_view);
Py_DECREF(buckets_view);
if(PyErr_Occurred()) {
return;
}
length = PyNumber_AsSsize_t(length_object, PyExc_OverflowError);
Py_DECREF(length_object);
if(PyErr_Occurred()) {
return;
}
if(length != buckets_length) {
PyErr_SetString(PyExc_ValueError, "Failed to write buckets");
return;
}
}
#endif
static const void *
hashindex_get(HashIndex *index, const void *key)
{
int idx = hashindex_lookup(index, key, NULL);
if(idx < 0) {
return NULL;
}
return BUCKET_ADDR(index, idx) + index->key_size;
}
static int
hashindex_set(HashIndex *index, const void *key, const void *value)
{
int start_idx;
int idx = hashindex_lookup(index, key, &start_idx);
uint8_t *ptr;
if(idx < 0)
{
if(index->num_entries > index->upper_limit) {
if(!hashindex_resize(index, grow_size(index->num_buckets))) {
return 0;
}
start_idx = hashindex_index(index, key);
}
idx = start_idx;
while(!BUCKET_IS_EMPTY(index, idx) && !BUCKET_IS_DELETED(index, idx)) {
idx = (idx + 1) % index->num_buckets;
}
if(BUCKET_IS_EMPTY(index, idx)){
index->num_empty--;
if(index->num_empty < index->min_empty) {
/* too many tombstones here / not enough empty buckets, do a same-size rebuild */
if(!hashindex_resize(index, index->num_buckets)) {
return 0;
}
}
}
ptr = BUCKET_ADDR(index, idx);
memcpy(ptr, key, index->key_size);
memcpy(ptr + index->key_size, value, index->value_size);
index->num_entries += 1;
}
else
{
memcpy(BUCKET_ADDR(index, idx) + index->key_size, value, index->value_size);
}
return 1;
}
static int
hashindex_delete(HashIndex *index, const void *key)
{
int idx = hashindex_lookup(index, key, NULL);
if (idx < 0) {
return 1;
}
BUCKET_MARK_DELETED(index, idx);
index->num_entries -= 1;
if(index->num_entries < index->lower_limit) {
if(!hashindex_resize(index, shrink_size(index->num_buckets))) {
return 0;
}
}
return 1;
}
static void *
hashindex_next_key(HashIndex *index, const void *key)
{
int idx = 0;
if(key) {
idx = 1 + (key - index->buckets) / index->bucket_size;
}
if (idx == index->num_buckets) {
return NULL;
}
while(BUCKET_IS_EMPTY(index, idx) || BUCKET_IS_DELETED(index, idx)) {
idx ++;
if (idx == index->num_buckets) {
return NULL;
}
}
return BUCKET_ADDR(index, idx);
}
static int
hashindex_len(HashIndex *index)
{
return index->num_entries;
}
static int
hashindex_size(HashIndex *index)
{
return sizeof(HashHeader) + index->num_buckets * index->bucket_size;
}
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