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Merge pull request #2250 from ThomasWaldmann/hashtable-minor-fix-m

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hashindex: rebuild hashtable if we have too little empty buckets, fixes #2246
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TW 2017-03-04 17:31:59 +01:00 committed by GitHub
commit 04eb7d77cc
1 changed files with 45 additions and 0 deletions
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45
src/borg/_hashindex.c
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@ -47,11 +47,13 @@ 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;
} HashIndex;
/* prime (or w/ big prime factors) hash table sizes
@ -77,6 +79,7 @@ static int hash_sizes[] = {
#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]))
@ -171,8 +174,10 @@ hashindex_resize(HashIndex *index, int capacity)
free(index->buckets);
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;
}
@ -191,6 +196,11 @@ int get_upper_limit(int 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);
@ -224,6 +234,19 @@ int shrink_size(int current){
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 */
static HashIndex *
hashindex_read(const char *path)
@ -303,6 +326,17 @@ hashindex_read(const char *path)
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);
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)) {
free(index->buckets);
free(index);
index = NULL;
goto fail;
}
}
fail:
if(fclose(fd) < 0) {
EPRINTF_PATH(path, "fclose failed");
@ -330,9 +364,11 @@ hashindex_init(int capacity, int key_size, int value_size)
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);
for(i = 0; i < capacity; i++) {
BUCKET_MARK_EMPTY(index, i);
}
@ -406,6 +442,15 @@ hashindex_set(HashIndex *index, const void *key, const void *value)
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);