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add performance based growth strategy

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This commit is contained in:
Jason Lu 2022-10-12 12:17:29 -07:00
parent 0d5c669c1c
commit 967119e981
1 changed files with 34 additions and 7 deletions
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41
src/Dict.h
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@ -51,8 +51,19 @@ constexpr uint32_t HASH_MASK = 0xFFFFFFFF; // only lower 32 bits.
// 2 for debug. 16 is best for a release build.
constexpr uint8_t DICT_REMAP_ENTRIES = 16;
// Load factor = 1 - 0.5 ^ LOAD_FACTOR_BITS. 0.75 is the optimal value for release builds.
constexpr uint8_t DICT_LOAD_FACTOR_BITS = 2;
// 100 for size < 1 << DICT_THRESHOLD_BITS + DICT_THRESHOLD_BITS;
// 75 for larger sizes
// 25 for min load factor.
constexpr int MIN_DICT_LOAD_FACTOR_100 = 25;
constexpr int DICT_LOAD_FACTOR_100 = 75;
// when space_distance is greater than SPACE_DISTANCE_THRESHOLD, double the size unless the load
// factor is already lower than MIN_DICT_LOAD_FACTOR_100.
constexpr int SPACE_DISTANCE_THRESHOLD = 32;
// To ignore occasional faraway spaces. only when space_distance_samples are above
// MIN_SPACE_DISTANCE_SAMPLES, we consider space_distance is not by chance.
constexpr int MIN_SPACE_DISTANCE_SAMPLES = 128;
// Default number of hash buckets in dictionary. The dictionary will
// increase the size of the hash table as needed.
@ -577,6 +588,17 @@ public:
max_entries = num_entries;
if ( num_entries > ThresholdEntries() )
SizeUp();
// if space_distance is too great, performance decreases. we need to sizeup for
// performance.
else if ( space_distance_samples > detail::MIN_SPACE_DISTANCE_SAMPLES &&
space_distance_sum > space_distance_samples * detail::SPACE_DISTANCE_THRESHOLD &&
int(num_entries) > detail::MIN_DICT_LOAD_FACTOR_100 * Capacity() / 100 )
{
SizeUp();
// reset performance metrics.
space_distance_sum = 0;
space_distance_samples = 0;
}
}
// Remap after insert can adjust asap to shorten period of mixed table.
@ -947,7 +969,7 @@ private:
int capacity = Capacity();
if ( log2_buckets <= detail::DICT_THRESHOLD_BITS )
return capacity; // 20 or less elements, 1.0, only size up when necessary.
return capacity - (capacity >> detail::DICT_LOAD_FACTOR_BITS);
return capacity * detail::DICT_LOAD_FACTOR_100 / 100;
}
// Used to improve the distribution of the original hash.
@ -1162,11 +1184,13 @@ private:
void InsertRelocateAndAdjust(detail::DictEntry<T>& entry, int insert_position)
{
/// e.distance is adjusted to be the one at insert_position.
#ifdef ZEEK_DICT_DEBUG
#ifdef DEBUG
entry.bucket = BucketByHash(entry.hash, log2_buckets);
#endif // ZEEK_DICT_DEBUG
#endif // DEBUG
int last_affected_position = insert_position;
InsertAndRelocate(entry, insert_position, &last_affected_position);
space_distance_sum += last_affected_position - insert_position;
space_distance_samples++;
// If remapping in progress, adjust the remap_end to step back a little to cover the new
// range if the changed range straddles over remap_end.
@ -1362,9 +1386,9 @@ private:
return false;
detail::DictEntry<T> entry = RemoveAndRelocate(
position); // no iteration cookies to adjust, no need for last_affected_position.
#ifdef ZEEK_DICT_DEBUG
#ifdef DEBUG
entry.bucket = expected;
#endif // ZEEK_DICT_DEBUG
#endif // DEBUG
// find insert position.
int insert_position = EndOfClusterByBucket(expected);
@ -1504,6 +1528,9 @@ private:
uint32_t num_entries = 0;
uint32_t max_entries = 0;
uint64_t cum_entries = 0;
int64_t space_distance_samples = 0;
// how far the space is
int64_t space_distance_sum = 0;
dict_delete_func delete_func = nullptr;
detail::DictEntry<T>* table = nullptr;