[commits] [tarantool] 02/04: vinyl: introduce bloom filters for partial key lookups
Vladimir Davydov
vdavydov.dev at gmail.com
Wed Mar 28 14:58:55 MSK 2018
On Wed, Mar 28, 2018 at 12:08:17AM +0300, Konstantin Osipov wrote:
> > +int
> > +tuple_bloom_builder_add(struct tuple_bloom_builder *builder,
> > + const struct tuple *tuple,
> > + const struct key_def *key_def,
> > + uint32_t hashed_parts)
> > +{
> > + assert(builder->part_count == key_def->part_count);
> > +
> > + uint32_t h = HASH_SEED;
> > + uint32_t carry = 0;
> > + uint32_t total_size = 0;
> > +
> > + for (uint32_t i = 0; i < key_def->part_count; i++) {
> > + total_size += tuple_hash_key_part(&h, &carry, tuple,
> > + &key_def->parts[i]);
>
> Is there a faster way to iterate over key parts?
> tuple_hash_key_part() involves tuple_field(). Are you assuming
> tuple_field() always has an offset map available?
Yes, as this is a key part. I can, of course, implement the optimization
done by tuple_hash_slowpath(), but I don't think it's worth it in this
particular case.
>
> > + if (i < hashed_parts)
> > + continue;
>
> Ugh, looks at first glance that we're invoking a hash function
> and iterating over key parts only to find out the total size.
> Then I see that you also calculate the hash value and carry as
> a side effect. If we can reuse hashed_parts, can't we reuse the
> hash of the hashed parts and the total size?
I guess we could, but I'm not sure it's worth the complexity it would
introduce. After all, this code is only called from a worker thread, no
point to over-optimize.
>
> > + struct tuple_hash_array *hash_arr = &builder->parts[i];
> > + if (hash_arr->count >= hash_arr->capacity) {
> > + uint32_t capacity = MAX(hash_arr->capacity * 2, 1024U);
> > + uint32_t *values = realloc(hash_arr->values,
> > + capacity * sizeof(*values));
> > + if (values == NULL) {
> > + diag_set(OutOfMemory, capacity * sizeof(*values),
> > + "malloc", "tuple hash array");
> > + return -1;
> > + }
> > + hash_arr->capacity = capacity;
> > + hash_arr->values = values;
>
> Sounds like we need an array data structure after all...
Yes, there are several places where we have to dynamically grow
an array of entries.
> Although I'd use a linked list of 4k blocks - I purposefully do not allow
> introducing arrays into the source code to avoid inefficient
> applications like this one.
True, in this particular case it isn't a problem to use a list of blocks
instead of a plain array. I'll rework.
>
> > + }
> > + uint32_t hash = PMurHash32_Result(h, carry, total_size);
> > + hash_arr->values[hash_arr->count++] = hash;
> > + }
> > + return 0;
> > +}
> > +
> > +struct tuple_bloom *
> > +tuple_bloom_new(struct tuple_bloom_builder *builder, double fpr)
> > +{
> > + uint32_t part_count = builder->part_count;
> > + size_t size = sizeof(struct tuple_bloom) +
> > + part_count * sizeof(struct bloom);
> > + struct tuple_bloom *bloom = malloc(size);
> > + if (bloom == NULL) {
> > + diag_set(OutOfMemory, size, "malloc", "tuple bloom");
> > + return NULL;
> > + }
> > + for (uint32_t i = 0; i < part_count; i++) {
> > + struct tuple_hash_array *hash_arr = &builder->parts[i];
> > + uint32_t count = hash_arr->count;
> > + if (bloom_create(&bloom->parts[i], count,
> > + fpr, runtime.quota) != 0) {
> > + diag_set(OutOfMemory, 0, "bloom_create",
> > + "tuple bloom part");
> > + for (uint32_t j = 0; j < i; j++)
> > + bloom_destroy(&bloom->parts[j], runtime.quota);
> > + free(bloom);
>
> Why can't use use tuple_bloom_delete() here?
> Looks like you need to introduce tuple_bloom_init() function for
> that.
If you insist.
>
> > + return NULL;
> > + }
> > + for (uint32_t k = 0; k < count; k++)
> > + bloom_add(&bloom->parts[i], hash_arr->values[k]);
> > + }
> > + bloom->part_count = part_count;
> > + return bloom;
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