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DataBlockHashIndex: Remove the division from EstimateSize() (#4293)

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Summary:
`BlockBasedTableBuilder::Add()` eventually calls
`DataBlockHashIndexBuilder::EstimateSize()`. The previous implementation
divides the `num_keys` by the `util_ratio_` to get an estimizted `num_buckets`.
Such division is expensive as it happens in every
`BlockBasedTableBuilder::Add()`.

This diff estimates the `num_buckets` by double addition instead of double
division. Specifically, in each `Add()`, we add `bucket_per_key_`
(inverse of `util_ratio_`) to the current `estimiated_num_buckets_`. The cost is
that we are gonna have the `estimated_num_buckets_` stored as one extra field
in the DataBlockHashIndexBuilder.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4293

Differential Revision: D9412472

Pulled By: fgwu

fbshipit-source-id: 2925c8509a401e7bd3c1ab1d9e9c7244755c277a
This commit is contained in:
Fenggang Wu 2018-08-20 23:04:08 -07:00 committed by Facebook Github Bot
parent 7188bd34f3
commit 6d37fdb365
3 changed files with 15 additions and 10 deletions
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1
table/block_builder.cc
View File

@ -106,7 +106,6 @@ size_t BlockBuilder::EstimateSizeAfterKV(const Slice& key, const Slice& value)
estimate += VarintLength(value.size()); // varint for value length.
}
// TODO(fwu): add the delta of the DataBlockHashIndex
return estimate;
}

8
table/data_block_hash_index.cc
View File

@ -23,12 +23,13 @@ void DataBlockHashIndexBuilder::Add(const Slice& key,
uint32_t hash_value = GetSliceHash(key);
hash_and_restart_pairs_.emplace_back(hash_value,
static_cast<uint8_t>(restart_index));
estimated_num_buckets_ += bucket_per_key_;
}
void DataBlockHashIndexBuilder::Finish(std::string& buffer) {
assert(Valid());
uint16_t num_buckets = static_cast<uint16_t>(
static_cast<double>(hash_and_restart_pairs_.size()) / util_ratio_);
uint16_t num_buckets = static_cast<uint16_t>(estimated_num_buckets_);
if (num_buckets == 0) {
num_buckets = 1; // sanity check
}
@ -66,8 +67,9 @@ void DataBlockHashIndexBuilder::Finish(std::string& buffer) {
}
void DataBlockHashIndexBuilder::Reset() {
hash_and_restart_pairs_.clear();
estimated_num_buckets_ = 0;
valid_ = true;
hash_and_restart_pairs_.clear();
}
void DataBlockHashIndex::Initialize(const char* data, uint16_t size,

16
table/data_block_hash_index.h
View File

@ -72,23 +72,26 @@ const double kDefaultUtilRatio = 0.75;
class DataBlockHashIndexBuilder {
public:
DataBlockHashIndexBuilder() : util_ratio_(0), valid_(false) {}
DataBlockHashIndexBuilder()
: bucket_per_key_(-1 /*uninitialized marker*/),
estimated_num_buckets_(0),
valid_(false) {}
void Initialize(double util_ratio) {
if (util_ratio <= 0) {
util_ratio = kDefaultUtilRatio; // sanity check
}
util_ratio_ = util_ratio;
bucket_per_key_ = 1 / util_ratio;
valid_ = true;
}
inline bool Valid() const { return valid_ && util_ratio_ > 0; }
inline bool Valid() const { return valid_ && bucket_per_key_ > 0; }
void Add(const Slice& key, const size_t restart_index);
void Finish(std::string& buffer);
void Reset();
inline size_t EstimateSize() const {
uint16_t estimated_num_buckets = static_cast<uint16_t>(
static_cast<double>(hash_and_restart_pairs_.size()) / util_ratio_);
uint16_t estimated_num_buckets =
static_cast<uint16_t>(estimated_num_buckets_);
// Maching the num_buckets number in DataBlockHashIndexBuilder::Finish.
estimated_num_buckets |= 1;
@ -98,7 +101,8 @@ class DataBlockHashIndexBuilder {
}
private:
double util_ratio_;
double bucket_per_key_; // is the multiplicative inverse of util_ratio_
double estimated_num_buckets_;
// Now the only usage for `valid_` is to mark false when the inserted
// restart_index is larger than supported. In this case HashIndex is not