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/**
* Copyright (C) 2018-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.
*/
#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kQuery
#include "mongo/platform/basic.h"
#include "mongo/s/query/establish_cursors.h"
#include <set>
#include "mongo/client/remote_command_retry_scheduler.h"
#include "mongo/client/remote_command_targeter.h"
#include "mongo/db/query/cursor_response.h"
#include "mongo/db/query/getmore_request.h"
#include "mongo/db/query/killcursors_request.h"
#include "mongo/executor/remote_command_request.h"
#include "mongo/executor/remote_command_response.h"
#include "mongo/s/async_requests_sender.h"
#include "mongo/s/grid.h"
#include "mongo/util/assert_util.h"
#include "mongo/util/log.h"
#include "mongo/util/scopeguard.h"
namespace mongo {
namespace {
/**
* This class wraps logic for establishing cursors using a MultiStatementTransactionRequestsSender.
*/
class CursorEstablisher {
public:
CursorEstablisher(OperationContext* opCtx,
executor::TaskExecutor* executor,
const NamespaceString& nss,
bool allowPartialResults)
: _opCtx(opCtx),
_executor{std::move(executor)},
_nss(nss),
_allowPartialResults(allowPartialResults) {}
/**
* Make a RequestSender and thus send requests.
*/
void sendRequests(const ReadPreferenceSetting readPref,
const std::vector<std::pair<ShardId, BSONObj>>& remotes,
Shard::RetryPolicy retryPolicy);
/**
* Wait for a single response via the RequestSender.
*/
void waitForResponse() noexcept;
/**
* Wait for all responses via the RequestSender.
*/
void waitForResponses() noexcept {
while (!_ars->done()) {
waitForResponse();
}
}
/**
* If any request recieved a non-retriable error response and partial results are not allowed,
* cancel any requests that may have succeeded and throw the first such error encountered.
*/
void checkForFailedRequests();
/**
* Take all cursors currently tracked by the CursorEstablsher.
*/
std::vector<RemoteCursor> takeCursors() {
return std::exchange(_remoteCursors, {});
};
private:
void _handleFailure(const AsyncRequestsSender::Response& response, Status status) noexcept;
OperationContext* const _opCtx;
executor::TaskExecutor* const _executor;
const NamespaceString _nss;
const bool _allowPartialResults;
std::unique_ptr<AsyncRequestsSender> _ars;
boost::optional<Status> _maybeFailure;
std::vector<RemoteCursor> _remoteCursors;
};
void CursorEstablisher::sendRequests(const ReadPreferenceSetting readPref,
const std::vector<std::pair<ShardId, BSONObj>>& remotes,
Shard::RetryPolicy retryPolicy) {
// Construct the requests
std::vector<AsyncRequestsSender::Request> requests;
for (const auto& remote : remotes) {
requests.emplace_back(remote.first, remote.second);
}
LOG(3) << "Establishing cursors on remotes {"
<< "opId: " << _opCtx->getOpID() << ","
<< "numRemotes: " << remotes.size() << "}";
// Send the requests
_ars = std::make_unique<AsyncRequestsSender>(
_opCtx, _executor, _nss.db().toString(), std::move(requests), readPref, retryPolicy);
}
void CursorEstablisher::waitForResponse() noexcept {
auto response = _ars->next();
try {
// Note the shardHostAndPort may not be populated if there was an error, so be sure
// to do this after parsing the cursor response to ensure the response was ok.
// Additionally, be careful not to push into 'remoteCursors' until we are sure we
// have a valid cursor, since the error handling path will attempt to clean up
// anything in 'remoteCursors'
auto responseData = uassertStatusOK(std::move(response.swResponse)).data;
auto cursorResponse = CursorResponse::parseFromBSONThrowing(std::move(responseData));
RemoteCursor cursor;
cursor.setCursorResponse(std::move(cursorResponse));
cursor.setShardId(std::move(response.shardId));
cursor.setHostAndPort(*response.shardHostAndPort);
_remoteCursors.push_back(std::move(cursor));
} catch (const DBException& ex) {
_handleFailure(response, ex.toStatus());
}
}
void CursorEstablisher::checkForFailedRequests() {
if (!_maybeFailure) {
// If we saw no failures, there is nothing to do.
return;
}
LOG(0) << "Unable to establish remote cursors - {"
<< "error: " << *_maybeFailure << ", "
<< "numActiveRemotes: " << _remoteCursors.size() << "}";
// Schedule killCursors against all cursors that were established.
for (const auto& remoteCursor : _remoteCursors) {
BSONObj cmdObj =
KillCursorsRequest(_nss, {remoteCursor.getCursorResponse().getCursorId()}).toBSON();
executor::RemoteCommandRequest request(
remoteCursor.getHostAndPort(), _nss.db().toString(), cmdObj, _opCtx);
// We do not process the response to the killCursors request (we make a good-faith
// attempt at cleaning up the cursors, but ignore any returned errors).
auto swHandle = _executor->scheduleRemoteCommand(
request, [](const executor::TaskExecutor::RemoteCommandCallbackArgs&) {});
if (!swHandle.isOK()) {
LOG(3) << "Unable to cancel remote cursor - " << swHandle.getStatus();
}
}
// Throw our failure.
uassertStatusOK(*_maybeFailure);
}
void CursorEstablisher::_handleFailure(const AsyncRequestsSender::Response& response,
Status status) noexcept {
LOG(3) << "Experienced a failure while establishing cursors - " << status;
if (_maybeFailure) {
// If we've already failed, just log and move on.
return;
}
// Retriable errors are swallowed if '_allowPartialResults' is true. Targeting shard replica
// sets can also throw FailedToSatisfyReadPreference, so we swallow it too.
bool isEligibleException = (ErrorCodes::isRetriableError(status.code()) ||
status.code() == ErrorCodes::FailedToSatisfyReadPreference);
if (_allowPartialResults && isEligibleException) {
// This exception is eligible to be swallowed.
return;
}
// Do not schedule any new requests.
_ars->stopRetrying();
_maybeFailure = std::move(status);
}
} // namespace
std::vector<RemoteCursor> establishCursors(OperationContext* opCtx,
executor::TaskExecutor* executor,
const NamespaceString& nss,
const ReadPreferenceSetting readPref,
const std::vector<std::pair<ShardId, BSONObj>>& remotes,
bool allowPartialResults,
Shard::RetryPolicy retryPolicy) {
auto establisher = CursorEstablisher(opCtx, executor, nss, allowPartialResults);
establisher.sendRequests(readPref, remotes, retryPolicy);
establisher.waitForResponses();
establisher.checkForFailedRequests();
return establisher.takeCursors();
}
} // namespace mongo
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