25bd139508
std::random_device() uses the relatively slow /dev/urandom, and we rarely if
ever intend to use it directly - we normally want to use it to seed a faster
random_engine (a pseudo-random number generator).
In many places in the code, we first created a random_device variable, and then
using it created a random_engine variable. However, this practice created the
risk of a programmer accidentally using the random_device object, instead of the
random_engine object, because both have the same API; This hurts performance.
This risk materialized in just two places in the code, utils/uuid.cc and
gms/gossiper.cc. A patch for to uuid.cc was sent previously by Pawel and is
not included in this patch, and the fix for gossiper.{cc,hh} is included here.
To avoid risking the same mistake in the future, this patch switches across the
code to an idiom where the random_device object is not *named*, so cannot be
accidentally used. We use the following idiom:
std::default_random_engine _engine{std::random_device{}()};
Here std::random_device{}() creates the random device (/dev/urandom) and pulls
a random integer from it. It then uses this seed to create the random_engine
(the pseudo-random number generator). The std::random_device{} object is
temporary and unnamed, and cannot be unintentionally used directly.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20180726154958.4405-1-nyh@scylladb.com>
114 lines
3.7 KiB
C++
114 lines
3.7 KiB
C++
/*
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* Licensed to the Apache Software Foundation (ASF) under one
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* or more contributor license agreements. See the NOTICE file
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* distributed with this work for additional information
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* regarding copyright ownership. The ASF licenses this file
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* to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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* Copyright (C) 2015 ScyllaDB
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*
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* Modified by ScyllaDB
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include <unordered_map>
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#include <seastar/core/future.hh>
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#include <seastar/core/distributed.hh>
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#include <seastar/core/timer.hh>
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#include <seastar/core/gate.hh>
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#include <seastar/core/metrics_registration.hh>
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#include "cql3/query_processor.hh"
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#include "gms/inet_address.hh"
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#include "db_clock.hh"
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namespace db {
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class batchlog_manager {
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private:
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static constexpr uint32_t replay_interval = 60 * 1000; // milliseconds
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static constexpr uint32_t page_size = 128; // same as HHOM, for now, w/out using any heuristics. TODO: set based on avg batch size.
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using clock_type = lowres_clock;
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struct stats {
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uint64_t write_attempts = 0;
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} _stats;
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seastar::metrics::metric_groups _metrics;
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size_t _total_batches_replayed = 0;
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cql3::query_processor& _qp;
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timer<clock_type> _timer;
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semaphore _sem{1};
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seastar::gate _gate;
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unsigned _cpu = 0;
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bool _stop = false;
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std::default_random_engine _e1{std::random_device{}()};
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future<> replay_all_failed_batches();
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public:
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// Takes a QP, not a distributes. Because this object is supposed
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// to be per shard and does no dispatching beyond delegating the the
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// shard qp (which is what you feed here).
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batchlog_manager(cql3::query_processor&);
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future<> start();
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future<> stop();
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future<> do_batch_log_replay();
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future<size_t> count_all_batches() const;
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size_t get_total_batches_replayed() const {
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return _total_batches_replayed;
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}
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mutation get_batch_log_mutation_for(const std::vector<mutation>&, const utils::UUID&, int32_t);
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mutation get_batch_log_mutation_for(const std::vector<mutation>&, const utils::UUID&, int32_t, db_clock::time_point);
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db_clock::duration get_batch_log_timeout() const;
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std::unordered_set<gms::inet_address> endpoint_filter(const sstring&, const std::unordered_map<sstring, std::unordered_set<gms::inet_address>>&);
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};
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extern distributed<batchlog_manager> _the_batchlog_manager;
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inline distributed<batchlog_manager>& get_batchlog_manager() {
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return _the_batchlog_manager;
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}
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inline batchlog_manager& get_local_batchlog_manager() {
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return _the_batchlog_manager.local();
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}
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}
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