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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.
*/
#pragma once
#include "mongo/platform/basic.h"
#include "mongo/client/read_preference.h"
namespace mongo {
/** Failpoint used to test hedged reads. */
extern FailPoint hedgedReadsSendRequestsToTargetHostsInAlphabeticalOrder;
/**
* HedgeOptions contains the information necessary for a particular command invocation to execute as
* a hedged read. Specifically, it contains:
* clang-format off
* (1) Whether or not the invocation should execute as a hedged read via `isHedgeEnabled`
* (2) How many hedged operations should be sent, in *addition* to the non-hedged/authoriative
* request (`hedgeCount`)
* (3) The maxTimeMS each hedge should be executed with (`maxTimeMSForHedgedReads`)
* clang-format on
*/
struct HedgeOptions {
bool isHedgeEnabled = false;
size_t hedgeCount = 0;
int maxTimeMSForHedgedReads = 0;
};
/**
* Return appropriate HedgeOptions for an invocation of the command named 'command' with
* read preference 'readPref.' A command invocation can execute as a hedged read if all three of the
* following conditions are met:
* clang-format off
* (1) The server has hedging globaly enabled
* (2) The read preference for the invocation allows for hedging
* (3) The command-type is read-only/is capable of hedging
* clang-format on
*/
HedgeOptions getHedgeOptions(StringData command, const ReadPreferenceSetting& readPref);
/**
* We ignore a subset of errors that may occur while running hedged operations (e.g., maxTimeMS
* expiration), as the operation may safely succeed despite their failure. For example, a network
* timeout error indicates the remote host experienced a timeout while running a remote-command as
* part of executing the hedged operation. This is by no means an indication that the operation has
* failed, as other hedged operations may still succeed. This function returns 'true' if we should
* ignore this error as a response to a hedged operation, and allow other hedges of the operation to
* possibly succeed.
* TODO SERVER-68704 will include other error categories that are safe to ignore.
*/
inline bool isIgnorableAsHedgeResult(const Status& status) {
return status == ErrorCodes::MaxTimeMSExpired || status == ErrorCodes::StaleDbVersion ||
ErrorCodes::isNetworkTimeoutError(status) || ErrorCodes::isStaleShardVersionError(status);
}
/**
* Orders HostAndPorts alphabetically; can be used by std::sort to order
* a range of HostAndPorts. We sort HostAndPorts alphabetically under
* test when targeting a set of HostAndPorts to hedge an operation, so tests
* can make assertions about which hosts receive authoritative vs. hedged requests.
*/
bool compareByLowerHostThenPort(const HostAndPort& a, const HostAndPort& b);
} // namespace mongo
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