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/**
* Copyright (C) 2020-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/executor/hedge_options_util.h"
#include "mongo/s/mongos_server_parameters_gen.h"
#include "mongo/util/sort.h"
#include "mongo/util/optional_util.h"
namespace mongo {
MONGO_FAIL_POINT_DEFINE(hedgedReadsSendRequestsToTargetHostsInAlphabeticalOrder);
namespace {
// Only do hedging for commands that cannot trigger writes.
constexpr std::array hedgeCommands{
"collStats"_sd,
"count"_sd,
"dataSize"_sd,
"dbStats"_sd,
"distinct"_sd,
"filemd5"_sd,
"find"_sd,
"listCollections"_sd,
"listIndexes"_sd,
"planCacheListFilters"_sd,
};
static_assert(constexprIsSorted(hedgeCommands.begin(), hedgeCommands.end()));
bool commandCanHedge(StringData command) {
return std::binary_search(hedgeCommands.begin(), hedgeCommands.end(), command);
}
bool commandShouldHedge(StringData command, const ReadPreferenceSetting& readPref) {
if (gReadHedgingMode.load() != ReadHedgingMode::kOn) {
return false; // Hedging is globally disabled.
}
auto&& mode = readPref.hedgingMode;
if (!mode || !mode->getEnabled()) {
return false; // The read preference didn't enable hedging.
}
return commandCanHedge(command);
}
template <typename IA, typename IB, typename F>
int compareTransformed(IA a1, IA a2, IB b1, IB b2, F&& f) {
for (;; ++a1, ++b1)
if (a1 == a2)
return b1 == b2 ? 0 : -1;
else if (b1 == b2)
return 1;
else if (int r = f(*a1) - f(*b1))
return r;
}
} // namespace
bool compareByLowerHostThenPort(const HostAndPort& a, const HostAndPort& b) {
const auto& ah = a.host();
const auto& bh = b.host();
if (int r = compareTransformed(
ah.begin(), ah.end(), bh.begin(), bh.end(), [](auto&& c) { return ctype::toLower(c); }))
return r < 0;
return a.port() < b.port();
}
HedgeOptions getHedgeOptions(StringData command, const ReadPreferenceSetting& readPref) {
bool shouldHedge = commandShouldHedge(command, readPref);
size_t hedgeCount = shouldHedge ? 1 : 0;
int maxTimeMSForHedgedReads = shouldHedge ? gMaxTimeMSForHedgedReads.load() : 0;
return {shouldHedge, hedgeCount, maxTimeMSForHedgedReads};
}
} // namespace mongo
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