diff options
Diffstat (limited to 'lib/gitlab/database/postgres_hll/batch_distinct_counter.rb')
| -rw-r--r-- | lib/gitlab/database/postgres_hll/batch_distinct_counter.rb | 62 |
1 files changed, 24 insertions, 38 deletions
diff --git a/lib/gitlab/database/postgres_hll/batch_distinct_counter.rb b/lib/gitlab/database/postgres_hll/batch_distinct_counter.rb index 33faa2ef1b0..62dfaeeaae3 100644 --- a/lib/gitlab/database/postgres_hll/batch_distinct_counter.rb +++ b/lib/gitlab/database/postgres_hll/batch_distinct_counter.rb @@ -16,9 +16,9 @@ module Gitlab # Grouped relations are NOT supported yet. # # @example Usage - # ::Gitlab::Database::PostgresHllBatchDistinctCount.new(::Project, :creator_id).estimate_distinct_count + # ::Gitlab::Database::PostgresHllBatchDistinctCount.new(::Project, :creator_id).execute # ::Gitlab::Database::PostgresHllBatchDistinctCount.new(::Project.with_active_services.service_desk_enabled.where(time_period)) - # .estimate_distinct_count( + # .execute( # batch_size: 1_000, # start: ::Project.with_active_services.service_desk_enabled.where(time_period).minimum(:id), # finish: ::Project.with_active_services.service_desk_enabled.where(time_period).maximum(:id) @@ -30,7 +30,6 @@ module Gitlab # for the most of a cases this value is lower. However, if the exact value is necessary other tools has to be used. class BatchDistinctCounter ERROR_RATE = 4.9 # max encountered empirical error rate, used in tests - FALLBACK = -1 MIN_REQUIRED_BATCH_SIZE = 750 SLEEP_TIME_IN_SECONDS = 0.01 # 10 msec sleep MAX_DATA_VOLUME = 4_000_000_000 @@ -38,8 +37,10 @@ module Gitlab # Each query should take < 500ms https://gitlab.com/gitlab-org/gitlab/-/merge_requests/22705 DEFAULT_BATCH_SIZE = 10_000 + ZERO_OFFSET = 1 + BUCKET_ID_MASK = (Buckets::TOTAL_BUCKETS - ZERO_OFFSET).to_s(2) BIT_31_MASK = "B'0#{'1' * 31}'" - BIT_9_MASK = "B'#{'0' * 23}#{'1' * 9}'" + BIT_32_NORMALIZED_BUCKET_ID_MASK = "B'#{'0' * (32 - BUCKET_ID_MASK.size)}#{BUCKET_ID_MASK}'" # @example source_query # SELECT CAST(('X' || md5(CAST(%{column} as text))) as bit(32)) attr_hash_32_bits # FROM %{relation} @@ -48,73 +49,58 @@ module Gitlab # AND %{column} IS NOT NULL BUCKETED_DATA_SQL = <<~SQL WITH hashed_attributes AS (%{source_query}) - SELECT (attr_hash_32_bits & #{BIT_9_MASK})::int AS bucket_num, + SELECT (attr_hash_32_bits & #{BIT_32_NORMALIZED_BUCKET_ID_MASK})::int AS bucket_num, (31 - floor(log(2, min((attr_hash_32_bits & #{BIT_31_MASK})::int))))::int as bucket_hash FROM hashed_attributes GROUP BY 1 SQL - TOTAL_BUCKETS_NUMBER = 512 + WRONG_CONFIGURATION_ERROR = Class.new(ActiveRecord::StatementInvalid) def initialize(relation, column = nil) @relation = relation @column = column || relation.primary_key end - def unwanted_configuration?(finish, batch_size, start) - batch_size <= MIN_REQUIRED_BATCH_SIZE || - (finish - start) >= MAX_DATA_VOLUME || - start > finish - end - - def estimate_distinct_count(batch_size: nil, start: nil, finish: nil) + # Executes counter that iterates over database source and return Gitlab::Database::PostgresHll::Buckets + # that can be used to estimation of number of uniq elements in analysed set + # + # @param batch_size maximal number of rows that will be analysed by single database query + # @param start initial pkey range + # @param finish final pkey range + # @return [Gitlab::Database::PostgresHll::Buckets] HyperLogLog data structure instance that can estimate number of unique elements + def execute(batch_size: nil, start: nil, finish: nil) raise 'BatchCount can not be run inside a transaction' if ActiveRecord::Base.connection.transaction_open? batch_size ||= DEFAULT_BATCH_SIZE - start = actual_start(start) finish = actual_finish(finish) - raise "Batch counting expects positive values only for #{@column}" if start < 0 || finish < 0 - return FALLBACK if unwanted_configuration?(finish, batch_size, start) + raise WRONG_CONFIGURATION_ERROR if unwanted_configuration?(start, finish, batch_size) batch_start = start - hll_blob = {} + hll_buckets = Buckets.new while batch_start <= finish begin - hll_blob.merge!(hll_blob_for_batch(batch_start, batch_start + batch_size)) {|_key, old, new| new > old ? new : old } + hll_buckets.merge_hash!(hll_buckets_for_batch(batch_start, batch_start + batch_size)) batch_start += batch_size end sleep(SLEEP_TIME_IN_SECONDS) end - estimate_cardinality(hll_blob) + hll_buckets end private - # arbitrary values that are present in #estimate_cardinality - # are sourced from https://www.sisense.com/blog/hyperloglog-in-pure-sql/ - # article, they are not representing any entity and serves as tune value - # for the whole equation - def estimate_cardinality(hll_blob) - num_zero_buckets = TOTAL_BUCKETS_NUMBER - hll_blob.size - - num_uniques = ( - ((TOTAL_BUCKETS_NUMBER**2) * (0.7213 / (1 + 1.079 / TOTAL_BUCKETS_NUMBER))) / - (num_zero_buckets + hll_blob.values.sum { |bucket_hash| 2**(-1 * bucket_hash)} ) - ).to_i - - if num_zero_buckets > 0 && num_uniques < 2.5 * TOTAL_BUCKETS_NUMBER - ((0.7213 / (1 + 1.079 / TOTAL_BUCKETS_NUMBER)) * (TOTAL_BUCKETS_NUMBER * - Math.log2(TOTAL_BUCKETS_NUMBER.to_f / num_zero_buckets))) - else - num_uniques - end + def unwanted_configuration?(start, finish, batch_size) + batch_size <= MIN_REQUIRED_BATCH_SIZE || + (finish - start) >= MAX_DATA_VOLUME || + start > finish || start < 0 || finish < 0 end - def hll_blob_for_batch(start, finish) + def hll_buckets_for_batch(start, finish) @relation .connection .execute(BUCKETED_DATA_SQL % { source_query: source_query(start, finish) }) |