LoadBalancer.php
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LoadBalancer.php
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	<?php
	/**
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* 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
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License along
	* with this program; if not, write to the Free Software Foundation, Inc.,
	* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
	* http://www.gnu.org/copyleft/gpl.html
	*
	* @file
	*/
	namespace Wikimedia\Rdbms;

	use ArrayUtils;
	use InvalidArgumentException;
	use Liuggio\StatsdClient\Factory\StatsdDataFactoryInterface;
	use LogicException;
	use Psr\Log\LoggerInterface;
	use Psr\Log\NullLogger;
	use RuntimeException;
	use Throwable;
	use UnexpectedValueException;
	use Wikimedia\ObjectCache\BagOStuff;
	use Wikimedia\ObjectCache\EmptyBagOStuff;
	use Wikimedia\ObjectCache\WANObjectCache;
	use Wikimedia\ScopedCallback;
	use Wikimedia\Stats\NullStatsdDataFactory;

	/**
	* @see ILoadBalancer
	* @ingroup Database
	*/
	class LoadBalancer implements ILoadBalancerForOwner {
	/** @var ILoadMonitor */
	private $loadMonitor;
	/** @var BagOStuff */
	private $srvCache;
	/** @var WANObjectCache */
	private $wanCache;
	/** @var DatabaseFactory */
	private $databaseFactory;

	/** @var TransactionProfiler */
	private $trxProfiler;
	/** @var StatsdDataFactoryInterface */
	private $statsd;
	/** @var LoggerInterface */
	private $logger;
	/** @var callable Exception logger */
	private $errorLogger;
	/** @var DatabaseDomain Local DB domain ID and default for new connections */
	private $localDomain;

	/** @var array<string,array<int,Database[]>> Map of (connection pool => server index => Database[]) */
	private $conns;

	/** @var string The name of the DB cluster */
	private $clusterName;
	/** @var ServerInfo */
	private $serverInfo;
	/** @var array<string,array<int,int\|float>> Map of (group => server index => weight) */
	private $groupLoads;
	/** @var string\|null Default query group to use with getConnection() */
	private $defaultGroup;

	/** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
	private $tableAliases = [];
	/** @var string[] Map of (index alias => index) */
	private $indexAliases = [];
	/** @var DatabaseDomain[]\|string[] Map of (domain alias => DB domain) */
	private $domainAliases = [];
	/** @var callable[] Map of (name => callable) */
	private $trxRecurringCallbacks = [];
	/** @var bool[] Map of (domain => whether to use "temp tables only" mode) */
	private $tempTablesOnlyMode = [];

	/** @var string\|false Explicit DBO_TRX transaction round active or false if none */
	private $trxRoundId = false;
	/** @var string Stage of the current transaction round in the transaction round life-cycle */
	private $trxRoundStage = self::ROUND_CURSORY;
	/** @var int[] The group replica server indexes keyed by group */
	private $readIndexByGroup = [];
	/** @var DBPrimaryPos\|null Replication sync position or false if not set */
	private $waitForPos;
	/** @var bool Whether a lagged replica DB was used */
	private $laggedReplicaMode = false;
	/** @var string\|false Reason this instance is read-only or false if not */
	private $readOnlyReason = false;
	/** @var int Total number of new connections ever made with this instance */
	private $connectionCounter = 0;
	/** @var bool */
	private $disabled = false;
	private ?ChronologyProtector $chronologyProtector = null;
	/** @var bool Whether the session consistency callback already executed */
	private $chronologyProtectorCalled = false;

	/** @var Database\|null The last connection handle that caused a problem */
	private $lastErrorConn;

	/** @var DatabaseDomain[] Map of (domain ID => domain instance) */
	private $nonLocalDomainCache = [];

	/**
	* @var int Modification counter for invalidating connections held by
	* DBConnRef instances. This is bumped by reconfigure().
	*/
	private $modcount = 0;

	/** The "server index" LB info key; see {@link IDatabase::getLBInfo()} */
	private const INFO_SERVER_INDEX = 'serverIndex';
	/** The "connection category" LB info key; see {@link IDatabase::getLBInfo()} */
	private const INFO_CONN_CATEGORY = 'connCategory';

	/** Warn when this many connection are held */
	private const CONN_HELD_WARN_THRESHOLD = 10;

	/** Default 'waitTimeout' when unspecified */
	private const MAX_WAIT_DEFAULT = 10;
	/** Seconds to cache primary DB server read-only status */
	private const TTL_CACHE_READONLY = 5;

	/** A category of connections that are tracked and transaction round aware */
	private const CATEGORY_ROUND = 'round';
	/** A category of connections that are tracked and in autocommit-mode */
	private const CATEGORY_AUTOCOMMIT = 'auto-commit';
	/** A category of connections that are untracked and in gauge-mode */
	private const CATEGORY_GAUGE = 'gauge';

	/** Transaction round, explicit or implicit, has not finished writing */
	private const ROUND_CURSORY = 'cursory';
	/** Transaction round writes are complete and ready for pre-commit checks */
	private const ROUND_FINALIZED = 'finalized';
	/** Transaction round passed final pre-commit checks */
	private const ROUND_APPROVED = 'approved';
	/** Transaction round was committed and post-commit callbacks must be run */
	private const ROUND_COMMIT_CALLBACKS = 'commit-callbacks';
	/** Transaction round was rolled back and post-rollback callbacks must be run */
	private const ROUND_ROLLBACK_CALLBACKS = 'rollback-callbacks';
	/** Transaction round encountered an error */
	private const ROUND_ERROR = 'error';

	/** @var int Idiom for getExistingReaderIndex() meaning "no index selected" */
	private const READER_INDEX_NONE = -1;

	public function __construct( array $params ) {
	$this->configure( $params );

	$this->conns = self::newTrackedConnectionsArray();
	}

	/**
	* @param array $params A database configuration array, see $wgLBFactoryConf.
	*
	* @return void
	*/
	protected function configure( array $params ): void {
	$this->localDomain = isset( $params['localDomain'] )
	? DatabaseDomain::newFromId( $params['localDomain'] )
	: DatabaseDomain::newUnspecified();

	$this->serverInfo = new ServerInfo();
	$this->groupLoads = [ self::GROUP_GENERIC => [] ];
	foreach ( $this->serverInfo->normalizeServerMaps( $params['servers'] ?? [] ) as $i => $server ) {
	$this->serverInfo->addServer( $i, $server );
	foreach ( $server['groupLoads'] as $group => $weight ) {
	$this->groupLoads[$group][$i] = $weight;
	}
	$this->groupLoads[self::GROUP_GENERIC][$i] = $server['load'];
	}
	// If the cluster name is not specified, fallback to the current primary name
	$this->clusterName = $params['clusterName']
	?? $this->serverInfo->getServerName( ServerInfo::WRITER_INDEX );

	if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
	$this->readOnlyReason = $params['readOnlyReason'];
	}

	$this->srvCache = $params['srvCache'] ?? new EmptyBagOStuff();
	$this->wanCache = $params['wanCache'] ?? WANObjectCache::newEmpty();

	// Note: this parameter is normally absent. It is injectable for testing purposes only.
	$this->databaseFactory = $params['databaseFactory'] ?? new DatabaseFactory( $params );

	$this->errorLogger = $params['errorLogger'] ?? static function ( Throwable $e ) {
	trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
	};
	$this->logger = $params['logger'] ?? new NullLogger();

	$this->trxProfiler = $params['trxProfiler'] ?? new TransactionProfiler();
	$this->statsd = $params['statsdDataFactory'] ?? new NullStatsdDataFactory();

	// Set up LoadMonitor
	$loadMonitorConfig = $params['loadMonitor'] ?? [ 'class' => LoadMonitorNull::class ];
	$compat = [
	'LoadMonitor' => LoadMonitor::class,
	'LoadMonitorNull' => LoadMonitorNull::class
	];
	$class = $loadMonitorConfig['class'];
	// @phan-suppress-next-line PhanImpossibleCondition
	if ( isset( $compat[$class] ) ) {
	$class = $compat[$class];
	}
	$this->loadMonitor = new $class(
	$this, $this->srvCache, $this->wanCache, $loadMonitorConfig );
	$this->loadMonitor->setLogger( $this->logger );
	$this->loadMonitor->setStatsdDataFactory( $this->statsd );

	if ( isset( $params['chronologyProtector'] ) ) {
	$this->chronologyProtector = $params['chronologyProtector'];
	}

	if ( isset( $params['roundStage'] ) ) {
	if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
	$this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
	} elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
	$this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
	}
	}

	$group = $params['defaultGroup'] ?? self::GROUP_GENERIC;
	$this->defaultGroup = isset( $this->groupLoads[ $group ] ) ? $group : self::GROUP_GENERIC;
	}

	private static function newTrackedConnectionsArray() {
	// Note that CATEGORY_GAUGE connections are untracked
	return [
	self::CATEGORY_ROUND => [],
	self::CATEGORY_AUTOCOMMIT => []
	];
	}

	public function getClusterName(): string {
	return $this->clusterName;
	}

	public function getLocalDomainID(): string {
	return $this->localDomain->getId();
	}

	public function resolveDomainID( $domain ): string {
	return $this->resolveDomainInstance( $domain )->getId();
	}

	/**
	* @param DatabaseDomain\|string\|false $domain
	* @return DatabaseDomain
	*/
	final protected function resolveDomainInstance( $domain ): DatabaseDomain {
	if ( $domain instanceof DatabaseDomain ) {
	return $domain; // already a domain instance
	} elseif ( $domain === false \|\| $domain === $this->localDomain->getId() ) {
	return $this->localDomain;
	} elseif ( isset( $this->domainAliases[$domain] ) ) {
	$this->domainAliases[$domain] =
	DatabaseDomain::newFromId( $this->domainAliases[$domain] );

	return $this->domainAliases[$domain];
	}

	$cachedDomain = $this->nonLocalDomainCache[$domain] ?? null;
	if ( $cachedDomain === null ) {
	$cachedDomain = DatabaseDomain::newFromId( $domain );
	$this->nonLocalDomainCache = [ $domain => $cachedDomain ];
	}

	return $cachedDomain;
	}

	/**
	* Get the first group in $groups with assigned servers, falling back to the default group
	*
	* @param string[]\|string\|false $groups Query group(s) in preference order, [], or false
	* @param int $i Specific server index or DB_PRIMARY/DB_REPLICA
	* @return string Query group
	*/
	private function resolveGroups( $groups, $i ) {
	// If a specific replica server was specified, then $groups makes no sense
	if ( $i > 0 && $groups !== [] && $groups !== false ) {
	$list = implode( ', ', (array)$groups );
	throw new LogicException( "Query group(s) ($list) given with server index (#$i)" );
	}

	if ( $groups === [] \|\| $groups === false \|\| $groups === $this->defaultGroup ) {
	$resolvedGroup = $this->defaultGroup;
	} elseif ( is_string( $groups ) ) {
	$resolvedGroup = isset( $this->groupLoads[$groups] ) ? $groups : $this->defaultGroup;
	} elseif ( is_array( $groups ) ) {
	$resolvedGroup = $this->defaultGroup;
	foreach ( $groups as $group ) {
	if ( isset( $this->groupLoads[$group] ) ) {
	$resolvedGroup = $group;
	break;
	}
	}
	} else {
	$resolvedGroup = $this->defaultGroup;
	}

	return $resolvedGroup;
	}

	/**
	* Sanitize connection flags provided by a call to getConnection()
	*
	* @param int $flags Bitfield of class CONN_* constants
	* @param string $domain Database domain
	* @return int Sanitized bitfield
	*/
	protected function sanitizeConnectionFlags( $flags, $domain ) {
	if ( self::fieldHasBit( $flags, self::CONN_TRX_AUTOCOMMIT ) ) {
	// Callers use CONN_TRX_AUTOCOMMIT to bypass REPEATABLE-READ staleness without
	// resorting to row locks (e.g. FOR UPDATE) or to make small out-of-band commits
	// during larger transactions. This is useful for avoiding lock contention.
	// Assuming all servers are of the same type (or similar), which is overwhelmingly
	// the case, use the primary server information to get the attributes. The information
	// for $i cannot be used since it might be DB_REPLICA, which might require connection
	// attempts in order to be resolved into a real server index.
	$attributes = $this->getServerAttributes( ServerInfo::WRITER_INDEX );
	if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
	// The RDBMS does not support concurrent writes (e.g. SQLite), so attempts
	// to use separate connections would just cause self-deadlocks. Note that
	// REPEATABLE-READ staleness is not an issue since DB-level locking means
	// that transactions are Strict Serializable anyway.
	$flags &= ~self::CONN_TRX_AUTOCOMMIT;
	$type = $this->serverInfo->getServerType( ServerInfo::WRITER_INDEX );
	$this->logger->info( __METHOD__ . ": CONN_TRX_AUTOCOMMIT disallowed ($type)" );
	} elseif ( isset( $this->tempTablesOnlyMode[$domain] ) ) {
	// T202116: integration tests are active and queries should be all be using
	// temporary clone tables (via prefix). Such tables are not visible across
	// different connections nor can there be REPEATABLE-READ snapshot staleness,
	// so use the same connection for everything.
	$flags &= ~self::CONN_TRX_AUTOCOMMIT;
	}
	}

	return $flags;
	}

	/**
	* @param IDatabase $conn
	* @param int $flags
	* @throws DBUnexpectedError
	*/
	private function enforceConnectionFlags( IDatabase $conn, $flags ) {
	if (
	self::fieldHasBit( $flags, self::CONN_TRX_AUTOCOMMIT ) \|\|
	// Handles with open transactions are avoided since they might be subject
	// to REPEATABLE-READ snapshots, which could affect the lag estimate query.
	self::fieldHasBit( $flags, self::CONN_UNTRACKED_GAUGE )
	) {
	if ( $conn->trxLevel() ) {
	throw new DBUnexpectedError(
	$conn,
	'Handle requested with autocommit-mode yet it has a transaction'
	);
	}

	$conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
	}
	}

	/**
	* @param array<int,int\|float> $loads Map of (server index => weight) for a load group
	* @param int\|float $sessionLagLimit Additional maximum lag threshold imposed by the session;
	* use INF if none applies. Servers will count as lagged if their lag exceeds either this
	* value or the configured "max lag" value.
	* @return int\|false Index of a non-lagged server with non-zero weight; false if none
	*/
	private function getRandomNonLagged( array $loads, $sessionLagLimit = INF ) {
	$lags = $this->getLagTimes();

	// Unset excessively lagged servers from the load group
	foreach ( $lags as $i => $lag ) {
	if ( $i !== ServerInfo::WRITER_INDEX ) {
	// How much lag normally counts as "excessive" for this server
	$maxServerLag = $this->serverInfo->getServerMaxLag( $i );
	// How much lag counts as "excessive" for this server given the session
	$maxServerLag = min( $maxServerLag, $sessionLagLimit );

	$srvName = $this->serverInfo->getServerName( $i );
	if ( $lag === false && !is_infinite( $maxServerLag ) ) {
	$this->logger->debug(
	__METHOD__ . ": server {db_server} is not replicating?",
	[ 'db_server' => $srvName ]
	);
	unset( $loads[$i] );
	} elseif ( $lag > $maxServerLag ) {
	$this->logger->debug(
	__METHOD__ .
	": server {db_server} has {lag} seconds of lag (>= {maxlag})",
	[ 'db_server' => $srvName, 'lag' => $lag, 'maxlag' => $maxServerLag ]
	);
	unset( $loads[$i] );
	}
	}
	}

	if ( array_sum( $loads ) == 0 ) {
	// All the replicas with non-zero weight are lagged and the primary has zero load.
	// Inform caller so that it can use switch to read-only mode and use a lagged replica.
	return false;
	}

	// Return a server index based on weighted random selection
	return ArrayUtils::pickRandom( $loads );
	}

	public function getReaderIndex( $group = false ) {
	$group = is_string( $group ) ? $group : self::GROUP_GENERIC;

	if ( !$this->serverInfo->hasReplicaServers() ) {
	// There is only one possible server to use (the primary)
	return ServerInfo::WRITER_INDEX;
	}

	$index = $this->getExistingReaderIndex( $group );
	if ( $index !== self::READER_INDEX_NONE ) {
	// A reader index was already selected for this query group. Keep using it,
	// since any session replication position was already waited on and any
	// active transaction will be reused (e.g. for point-in-time snapshots).
	return $index;
	}

	// Get the server weight array for this load group
	$loads = $this->groupLoads[$group] ?? [];
	if ( !$loads ) {
	$this->logger->info( __METHOD__ . ": no loads for group $group" );
	return false;
	}

	// Load any session replication positions, before any connection attempts,
	// since reading them afterwards can only cause more delay due to possibly
	// seeing even higher replication positions (e.g. from concurrent requests).
	$this->loadSessionPrimaryPos();

	// Scale the configured load weights according to each server's load/state.
	// This can sometimes trigger server connections due to cache regeneration.
	$this->loadMonitor->scaleLoads( $loads );

	// Pick a server, accounting for load weights, lag, and session consistency
	$i = $this->pickReaderIndex( $loads );
	if ( $i === false ) {
	// Connection attempts failed
	return false;
	}

	// If data seen by queries is expected to reflect writes from a prior transaction,
	// then wait for the chosen server to apply those changes. This is used to improve
	// session consistency.
	if ( !$this->awaitSessionPrimaryPos( $i ) ) {
	// Data will be outdated compared to what was expected
	$this->setLaggedReplicaMode();
	}

	// Keep using this server for DB_REPLICA handles for this group
	if ( $i < 0 ) {
	throw new UnexpectedValueException( "Cannot set a negative read server index" );
	}
	$this->readIndexByGroup[$group] = $i;

	$serverName = $this->getServerName( $i );
	$this->logger->debug( __METHOD__ . ": using server $serverName for group '$group'" );

	return $i;
	}

	/**
	* Get the server index chosen for DB_REPLICA connections for the given query group
	*
	* @param string $group Query group; use false for the generic group
	* @return int Specific server index or LoadBalancer::READER_INDEX_NONE if none was chosen
	*/
	protected function getExistingReaderIndex( $group ) {
	return $this->readIndexByGroup[$group] ?? self::READER_INDEX_NONE;
	}

	/**
	* Pick a server that is reachable and preferably non-lagged based on the load weights
	*
	* This will leave the server connection open within the pool for reuse
	*
	* @param array<int,int\|float> $loads Map of (server index => weight) for a load group
	* @return int\|false Server index to use as the load group reader index; false on failure
	*/
	private function pickReaderIndex( array $loads ) {
	if ( $loads === [] ) {
	throw new InvalidArgumentException( "Load group array is empty" );
	}

	$i = false;
	// Quickly look through the available servers for a server that meets criteria...
	$currentLoads = $loads;
	while ( count( $currentLoads ) ) {
	if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
	$this->logger->debug( __METHOD__ . ": session has replication position" );
	// ChronologyProtector::getSessionPrimaryPos called in loadSessionPrimaryPos()
	// sets "waitForPos" for session consistency. This triggers doWait() after
	// connect, so it's especially good to avoid lagged servers so as to avoid
	// excessive delay in that method.
	$ago = microtime( true ) - $this->waitForPos->asOfTime();
	// Aim for <= 1 second of waiting (being too picky can backfire)
	$i = $this->getRandomNonLagged( $currentLoads, $ago + 1 );
	} else {
	// Any server with less lag than it's 'max lag' param is preferable
	$i = $this->getRandomNonLagged( $currentLoads );
	}

	if ( $i === false && count( $currentLoads ) ) {
	$this->setLaggedReplicaMode();
	// All replica DBs lagged, just pick anything.
	$i = ArrayUtils::pickRandom( $currentLoads );
	}

	if ( $i === false ) {
	// pickRandom() returned false.
	// This is permanent and means the configuration or LoadMonitor
	// wants us to return false.
	$this->logger->debug( __METHOD__ . ": no suitable server found" );
	return false;
	}

	$serverName = $this->getServerName( $i );
	$this->logger->debug( __METHOD__ . ": connecting to $serverName..." );

	// Get a connection to this server without triggering complementary connections
	// to other servers (due to things like lag or read-only checks). We want to avoid
	// the risk of overhead and recursion here.
	$conn = $this->getServerConnection( $i, self::DOMAIN_ANY, self::CONN_SILENCE_ERRORS );
	if ( !$conn ) {
	$this->logger->warning( __METHOD__ . ": failed connecting to $serverName" );
	unset( $currentLoads[$i] ); // avoid this server next iteration
	continue;
	}

	// Return this server
	break;
	}

	// If all servers were down, quit now
	if ( $currentLoads === [] ) {
	$this->logger->error( __METHOD__ . ": all servers down" );
	}

	return $i;
	}

	public function waitForAll( DBPrimaryPos $pos, $timeout = null ) {
	$timeout = $timeout ?: self::MAX_WAIT_DEFAULT;

	$oldPos = $this->waitForPos;
	try {
	$this->waitForPos = $pos;

	$failedReplicas = [];
	foreach ( $this->serverInfo->getStreamingReplicaIndexes() as $i ) {
	if ( $this->serverHasLoadInAnyGroup( $i ) ) {
	$start = microtime( true );
	$ok = $this->awaitSessionPrimaryPos( $i, $timeout );
	if ( !$ok ) {
	$failedReplicas[] = $this->getServerName( $i );
	}
	$timeout -= intval( microtime( true ) - $start );
	}
	}

	// Stop spamming logs when only one replica is lagging and we have 5+ replicas.
	// Mediawiki automatically stops sending queries to the lagged one.
	$failed = $failedReplicas && ( count( $failedReplicas ) > 1 \|\| $this->getServerCount() < 5 );
	if ( $failed ) {
	$this->logger->error(
	"Timed out waiting for replication to reach {raw_pos}",
	[
	'raw_pos' => $pos->__toString(),
	'failed_hosts' => $failedReplicas,
	'timeout' => $timeout,
	'exception' => new RuntimeException()
	]
	);
	}

	return !$failed;
	} finally {
	// Restore the old position; this is used for throttling, not lag-protection
	$this->waitForPos = $oldPos;
	}
	}

	/**
	* @param int $i Specific server index
	* @return bool
	*/
	private function serverHasLoadInAnyGroup( $i ) {
	foreach ( $this->groupLoads as $loadsByIndex ) {
	if ( ( $loadsByIndex[$i] ?? 0 ) > 0 ) {
	return true;
	}
	}

	return false;
	}

	public function getAnyOpenConnection( $i, $flags = 0 ) {
	$i = ( $i === self::DB_PRIMARY ) ? ServerInfo::WRITER_INDEX : $i;
	$conn = false;
	foreach ( $this->conns as $type => $poolConnsByServer ) {
	if ( $i === self::DB_REPLICA ) {
	// Consider all existing connections to any server
	$applicableConnsByServer = $poolConnsByServer;
	} else {
	// Consider all existing connections to a specific server
	$applicableConnsByServer = isset( $poolConnsByServer[$i] )
	? [ $i => $poolConnsByServer[$i] ]
	: [];
	}

	$conn = $this->pickAnyOpenConnection( $applicableConnsByServer );
	if ( $conn ) {
	$this->logger->debug( __METHOD__ . ": found '$type' connection to #$i." );
	break;
	}
	}

	if ( $conn ) {
	$this->enforceConnectionFlags( $conn, $flags );
	}

	return $conn;
	}

	/**
	* @param Database[][] $connsByServer Map of (server index => array of DB handles)
	* @return IDatabaseForOwner\|false An appropriate open connection or false if none found
	*/
	private function pickAnyOpenConnection( array $connsByServer ) {
	foreach ( $connsByServer as $i => $conns ) {
	foreach ( $conns as $conn ) {
	if ( !$conn->isOpen() ) {
	$this->logger->warning(
	__METHOD__ .
	": pooled DB handle for {db_server} (#$i) has no open connection.",
	$this->getConnLogContext( $conn )
	);
	continue; // some sort of error occurred?
	}
	return $conn;
	}
	}

	return false;
	}

	/**
	* Wait for a given replica DB to catch up to the primary DB pos stored in "waitForPos"
	*
	* @see loadSessionPrimaryPos()
	*
	* @param int $index Specific server index
	* @param int\|null $timeout Max seconds to wait; default is "waitTimeout"
	* @return bool Success
	*/
	private function awaitSessionPrimaryPos( $index, $timeout = null ) {
	$timeout = max( 1, intval( $timeout ?: self::MAX_WAIT_DEFAULT ) );

	if ( !$this->waitForPos \|\| $index === ServerInfo::WRITER_INDEX ) {
	return true;
	}

	$srvName = $this->getServerName( $index );

	// Check if we already know that the DB has reached this point
	$key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $srvName, 'v2' );

	/** @var DBPrimaryPos $knownReachedPos */
	$position = $this->srvCache->get( $key );
	if ( !is_array( $position ) ) {
	$knownReachedPos = null;
	} else {
	$class = $position['_type_'];
	$knownReachedPos = $class::newFromArray( $position );
	}
	if (
	$knownReachedPos instanceof DBPrimaryPos &&
	$knownReachedPos->hasReached( $this->waitForPos )
	) {
	$this->logger->debug(
	__METHOD__ .
	": replica DB {db_server} known to be caught up (pos >= $knownReachedPos).",
	[ 'db_server' => $srvName ]
	);

	return true;
	}

	$close = false; // close the connection afterwards
	$flags = self::CONN_SILENCE_ERRORS;
	// Check if there is an existing connection that can be used
	$conn = $this->getAnyOpenConnection( $index, $flags );
	if ( !$conn ) {
	// Get a connection to this server without triggering complementary connections
	// to other servers (due to things like lag or read-only checks). We want to avoid
	// the risk of overhead and recursion here.
	$conn = $this->getServerConnection( $index, self::DOMAIN_ANY, $flags );
	if ( !$conn ) {
	$this->logger->warning(
	__METHOD__ . ': failed to connect to {db_server}',
	[ 'db_server' => $srvName ]
	);

	return false;
	}
	// Avoid connection spam in waitForAll() when connections
	// are made just for the sake of doing this lag check.
	$close = true;
	}

	$this->logger->info(
	__METHOD__ .
	': waiting for replica DB {db_server} to catch up...',
	$this->getConnLogContext( $conn )
	);

	$result = $conn->primaryPosWait( $this->waitForPos, $timeout );

	$ok = ( $result !== null && $result != -1 );
	if ( $ok ) {
	// Remember that the DB reached this point
	$this->srvCache->set( $key, $this->waitForPos->toArray(), BagOStuff::TTL_DAY );
	}

	if ( $close ) {
	$this->closeConnection( $conn );
	}

	return $ok;
	}

	public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
	if ( self::fieldHasBit( $flags, self::CONN_SILENCE_ERRORS ) ) {
	throw new UnexpectedValueException(
	__METHOD__ . ' got CONN_SILENCE_ERRORS; connection is already deferred'
	);
	}

	$domain = $this->resolveDomainID( $domain );
	$role = ( $i === self::DB_PRIMARY \|\| $i === ServerInfo::WRITER_INDEX )
	? self::DB_PRIMARY
	: self::DB_REPLICA;

	return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role, $this->modcount );
	}

	public function getConnectionInternal( $i, $groups = [], $domain = false, $flags = 0 ): IDatabase {
	$domain = $this->resolveDomainID( $domain );
	$group = $this->resolveGroups( $groups, $i );
	$flags = $this->sanitizeConnectionFlags( $flags, $domain );
	// If given DB_PRIMARY/DB_REPLICA, resolve it to a specific server index. Resolving
	// DB_REPLICA might trigger getServerConnection() calls due to the getReaderIndex()
	// connectivity checks or LoadMonitor::scaleLoads() server state cache regeneration.
	// The use of getServerConnection() instead of getConnection() avoids infinite loops.
	$serverIndex = $i;
	if ( $i === self::DB_PRIMARY ) {
	$serverIndex = ServerInfo::WRITER_INDEX;
	} elseif ( $i === self::DB_REPLICA ) {
	$groupIndex = $this->getReaderIndex( $group );
	if ( $groupIndex !== false ) {
	// Group connection succeeded
	$serverIndex = $groupIndex;
	}
	if ( $serverIndex < 0 ) {
	$this->reportConnectionError( 'could not connect to any replica DB server' );
	}
	} elseif ( !$this->serverInfo->hasServerIndex( $i ) ) {
	throw new UnexpectedValueException( "Invalid server index index #$i" );
	}
	// Get an open connection to that server (might trigger a new connection)
	return $this->getServerConnection( $serverIndex, $domain, $flags );
	}

	public function getServerConnection( $i, $domain, $flags = 0 ) {
	$domainInstance = DatabaseDomain::newFromId( $domain );
	// Number of connections made before getting the server index and handle
	$priorConnectionsMade = $this->connectionCounter;
	// Get an open connection to this server (might trigger a new connection)
	$conn = $this->reuseOrOpenConnectionForNewRef( $i, $domainInstance, $flags );
	// Throw an error or otherwise bail out if the connection attempt failed
	if ( !( $conn instanceof IDatabaseForOwner ) ) {
	if ( !self::fieldHasBit( $flags, self::CONN_SILENCE_ERRORS ) ) {
	$this->reportConnectionError();
	}

	return false;
	}

	// Profile any new connections caused by this method
	if ( $this->connectionCounter > $priorConnectionsMade ) {
	$this->trxProfiler->recordConnection(
	$conn->getServerName(),
	$conn->getDBname(),
	( $i === ServerInfo::WRITER_INDEX && $this->hasStreamingReplicaServers() )
	);
	}

	if ( !$conn->isOpen() ) {
	$this->lastErrorConn = $conn;
	// Connection was made but later unrecoverably lost for some reason.
	// Do not return a handle that will just throw exceptions on use, but
	// let the calling code, e.g. getReaderIndex(), try another server.
	if ( !self::fieldHasBit( $flags, self::CONN_SILENCE_ERRORS ) ) {
	$this->reportConnectionError();
	}
	return false;
	}

	return $conn;
	}

	/**
	* @deprecated since 1.39.
	*/
	public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ): DBConnRef {
	wfDeprecated( __METHOD__, '1.39' );
	// @phan-suppress-next-line PhanTypeMismatchReturnSuperType to be removed soon
	return $this->getConnection( $i, $groups, $domain, $flags );
	}

	public function getMaintenanceConnectionRef(
	$i,
	$groups = [],
	$domain = false,
	$flags = 0
	): DBConnRef {
	if ( self::fieldHasBit( $flags, self::CONN_SILENCE_ERRORS ) ) {
	throw new UnexpectedValueException(
	__METHOD__ . ' CONN_SILENCE_ERRORS is not supported'
	);
	}

	$domain = $this->resolveDomainID( $domain );
	$role = ( $i === self::DB_PRIMARY \|\| $i === ServerInfo::WRITER_INDEX )
	? self::DB_PRIMARY
	: self::DB_REPLICA;

	return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role, $this->modcount );
	}

	/**
	* Get a live connection handle to the given domain
	*
	* This will reuse an existing tracked connection when possible. In some cases, this
	* involves switching the DB domain of an existing handle in order to reuse it. If no
	* existing handles can be reused, then a new connection will be made.
	*
	* @param int $i Specific server index
	* @param DatabaseDomain $domain Database domain ID required by the reference
	* @param int $flags Bit field of class CONN_* constants
	* @return IDatabase\|null Database or null on error
	* @throws DBError When database selection fails
	* @throws InvalidArgumentException When the server index is invalid
	* @throws UnexpectedValueException When the DB domain of the connection is corrupted
	* @throws DBAccessError If disable() was called
	*/
	private function reuseOrOpenConnectionForNewRef( $i, DatabaseDomain $domain, $flags = 0 ) {
	// Figure out which connection pool to use based on the flags
	if ( $this->fieldHasBit( $flags, self::CONN_UNTRACKED_GAUGE ) ) {
	// Use low timeouts, use autocommit mode, ignore transaction rounds
	$category = self::CATEGORY_GAUGE;
	} elseif ( self::fieldHasBit( $flags, self::CONN_TRX_AUTOCOMMIT ) ) {
	// Use autocommit mode, ignore transaction rounds
	$category = self::CATEGORY_AUTOCOMMIT;
	} else {
	// Respect DBO_DEFAULT, respect transaction rounds
	$category = self::CATEGORY_ROUND;
	}

	$conn = null;
	// Reuse a free connection in the pool from any domain if possible. There should only
	// be one connection in this pool unless either:
	// - a) IDatabase::databasesAreIndependent() returns true (e.g. postgres) and two
	// or more database domains have been used during the load balancer's lifetime
	// - b) Two or more nested function calls used getConnection() on different domains.
	foreach ( ( $this->conns[$category][$i] ?? [] ) as $poolConn ) {
	// Check if any required DB domain changes for the new reference are possible
	// Calling selectDomain() would trigger a reconnect, which will break if a
	// transaction is active or if there is any other meaningful session state.
	$isShareable = !(
	$poolConn->databasesAreIndependent() &&
	$domain->getDatabase() !== null &&
	$domain->getDatabase() !== $poolConn->getDBname()
	);
	if ( $isShareable ) {
	$conn = $poolConn;
	// Make any required DB domain changes for the new reference
	if ( !$domain->isUnspecified() ) {
	$conn->selectDomain( $domain );
	}
	$this->logger->debug( __METHOD__ . ": reusing connection for $i/$domain" );
	break;
	}
	}

	// If necessary, try to open a new connection and add it to the pool
	if ( !$conn ) {
	$conn = $this->reallyOpenConnection(
	$i,
	$domain,
	[ self::INFO_CONN_CATEGORY => $category ]
	);
	if ( $conn->isOpen() ) {
	// Make Database::isReadOnly() respect server-side and configuration-based
	// read-only mode. Note that replica handles are always seen as read-only
	// in Database::isReadOnly() and Database::assertIsWritablePrimary().
	if ( $i === ServerInfo::WRITER_INDEX ) {
	if ( $this->readOnlyReason !== false ) {
	$readOnlyReason = $this->readOnlyReason;
	} elseif ( $this->isPrimaryRunningReadOnly( $conn ) ) {
	$readOnlyReason = 'The primary database server is running in read-only mode.';
	} else {
	$readOnlyReason = false;
	}
	$conn->setLBInfo( $conn::LB_READ_ONLY_REASON, $readOnlyReason );
	}
	// Connection obtained; check if it belongs to a tracked connection category
	if ( isset( $this->conns[$category] ) ) {
	// Track this connection for future reuse
	$this->conns[$category][$i][] = $conn;
	}
	} else {
	$this->logger->warning( __METHOD__ . ": connection error for $i/$domain" );
	$this->lastErrorConn = $conn;
	$conn = null;
	}
	}

	if ( $conn instanceof IDatabaseForOwner ) {
	// Check to make sure that the right domain is selected
	$this->assertConnectionDomain( $conn, $domain );
	// Check to make sure that the CONN_* flags are respected
	$this->enforceConnectionFlags( $conn, $flags );
	}

	return $conn;
	}

	/**
	* Sanity check to make sure that the right domain is selected
	*
	* @param Database $conn
	* @param DatabaseDomain $domain
	* @throws DBUnexpectedError
	*/
	private function assertConnectionDomain( Database $conn, DatabaseDomain $domain ) {
	if ( !$domain->isCompatible( $conn->getDomainID() ) ) {
	throw new UnexpectedValueException(
	"Got connection to '{$conn->getDomainID()}', but expected one for '{$domain}'"
	);
	}
	}

	public function getServerAttributes( $i ) {
	return $this->databaseFactory->attributesFromType(
	$this->getServerType( $i ),
	$this->serverInfo->getServerDriver( $i )
	);
	}

	/**
	* Open a new network connection to a server (uncached)
	*
	* Returns a Database object whether or not the connection was successful.
	*
	* @param int $i Specific server index
	* @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
	* @param array $lbInfo Additional information for setLBInfo()
	* @return Database
	* @throws DBAccessError
	* @throws InvalidArgumentException
	*/
	protected function reallyOpenConnection( $i, DatabaseDomain $domain, array $lbInfo ) {
	if ( $this->disabled ) {
	throw new DBAccessError();
	}

	$server = $this->serverInfo->getServerInfoStrict( $i );
	if ( $lbInfo[self::INFO_CONN_CATEGORY] === self::CATEGORY_GAUGE ) {
	// Use low connection/read timeouts for connection used for gauging server health.
	// Gauge information should be cached and used to avoid outages. Indefinite hanging
	// while gauging servers would do the opposite.
	$server['connectTimeout'] = min( 1, $server['connectTimeout'] ?? INF );
	$server['receiveTimeout'] = min( 1, $server['receiveTimeout'] ?? INF );
	// Avoid implicit transactions and avoid any SET query for session variables during
	// Database::open(). If a server becomes slow, every extra query can cause significant
	// delays, even with low connect/receive timeouts.
	$server['flags'] ??= 0;
	$server['flags'] &= ~IDatabase::DBO_DEFAULT;
	$server['flags'] \|= IDatabase::DBO_GAUGE;
	} else {
	// Use implicit transactions unless explicitly configured otherwise
	$server['flags'] ??= IDatabase::DBO_DEFAULT;
	}

	if ( !empty( $server['is static'] ) ) {
	$topologyRole = IDatabase::ROLE_STATIC_CLONE;
	} else {
	$topologyRole = ( $i === ServerInfo::WRITER_INDEX )
	? IDatabase::ROLE_STREAMING_MASTER
	: IDatabase::ROLE_STREAMING_REPLICA;
	}

	$conn = $this->databaseFactory->create(
	$server['type'],
	array_merge( $server, [
	// Basic replication role information
	'topologyRole' => $topologyRole,
	// Use the database specified in $domain (null means "none or entrypoint DB");
	// fallback to the $server default if the RDBMs is an embedded library using a
	// file on disk since there would be nothing to access to without a DB/file name.
	'dbname' => $this->getServerAttributes( $i )[Database::ATTR_DB_IS_FILE]
	? ( $domain->getDatabase() ?? $server['dbname'] ?? null )
	: $domain->getDatabase(),
	// Override the $server default schema with that of $domain if specified
	'schema' => $domain->getSchema(),
	// Use the table prefix specified in $domain
	'tablePrefix' => $domain->getTablePrefix(),
	'srvCache' => $this->srvCache,
	'logger' => $this->logger,
	'errorLogger' => $this->errorLogger,
	'trxProfiler' => $this->trxProfiler,
	'lbInfo' => [ self::INFO_SERVER_INDEX => $i ] + $lbInfo
	] ),
	Database::NEW_UNCONNECTED
	);
	// Set alternative table/index names before any queries can be issued
	$conn->setTableAliases( $this->tableAliases );
	$conn->setIndexAliases( $this->indexAliases );
	// Account for any active transaction round and listeners
	if ( $i === ServerInfo::WRITER_INDEX ) {
	if ( $this->trxRoundId !== false ) {
	$this->applyTransactionRoundFlags( $conn );
	}
	foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
	$conn->setTransactionListener( $name, $callback );
	}
	}

	// Make the connection handle live
	try {
	$conn->initConnection();
	++$this->connectionCounter;
	} catch ( DBConnectionError $e ) {
	$this->lastErrorConn = $conn;
	// ignore; let the DB handle the logging
	}

	if ( $conn->isOpen() ) {
	$this->logger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
	} else {
	$this->logger->warning(
	__METHOD__ . ": connection error for $i/{db_domain}",
	[ 'db_domain' => $domain->getId() ]
	);
	}

	// Log when many connection are made during a single request/script
	$count = 0;
	foreach ( $this->conns as $poolConnsByServer ) {
	foreach ( $poolConnsByServer as $serverConns ) {
	$count += count( $serverConns );
	}
	}
	if ( $count >= self::CONN_HELD_WARN_THRESHOLD ) {
	$this->logger->warning(
	__METHOD__ . ": {connections}+ connections made (primary={primarydb})",
	$this->getConnLogContext(
	$conn,
	[
	'connections' => $count,
	'primarydb' => $this->serverInfo->getPrimaryServerName(),
	'db_domain' => $domain->getId()
	]
	)
	);
	}

	$this->assertConnectionDomain( $conn, $domain );

	return $conn;
	}

	/**
	* Make sure that any "waitForPos" replication positions are loaded and available
	*
	* Each load balancer cluster has up to one replication position for the session.
	* These are used when data read by queries is expected to reflect writes caused
	* by a prior request/script from the same client.
	*
	* @see awaitSessionPrimaryPos()
	*/
	private function loadSessionPrimaryPos() {
	if ( !$this->chronologyProtectorCalled && $this->chronologyProtector ) {
	$this->chronologyProtectorCalled = true;
	$pos = $this->chronologyProtector->getSessionPrimaryPos( $this );
	$this->logger->debug( __METHOD__ . ': executed chronology callback.' );
	if ( $pos ) {
	if ( !$this->waitForPos \|\| $pos->hasReached( $this->waitForPos ) ) {
	$this->waitForPos = $pos;
	}
	}
	}
	}

	/**
	* @param string $extraLbError Separat load balancer error
	* @throws DBConnectionError
	* @return never
	*/
	private function reportConnectionError( $extraLbError = '' ) {
	if ( $this->lastErrorConn instanceof IDatabaseForOwner ) {
	$srvName = $this->lastErrorConn->getServerName();
	$lastDbError = $this->lastErrorConn->lastError() ?: 'unknown error';

	$exception = new DBConnectionError(
	$this->lastErrorConn,
	$extraLbError
	? "{$extraLbError}; {$lastDbError} ({$srvName})"
	: "{$lastDbError} ({$srvName})"
	);

	if ( $extraLbError ) {
	$this->logger->warning(
	__METHOD__ . ": $extraLbError; {last_error} ({db_server})",
	$this->getConnLogContext(
	$this->lastErrorConn,
	[
	'method' => __METHOD__,
	'last_error' => $lastDbError
	]
	)
	);
	}
	} else {
	$exception = new DBConnectionError(
	null,
	$extraLbError ?: 'could not connect to the DB server'
	);

	if ( $extraLbError ) {
	$this->logger->error(
	__METHOD__ . ": $extraLbError",
	[
	'method' => __METHOD__,
	'last_error' => '(last connection error missing)'
	]
	);
	}
	}

	throw $exception;
	}

	public function getServerCount() {
	return $this->serverInfo->getServerCount();
	}

	public function hasReplicaServers() {
	return $this->serverInfo->hasReplicaServers();
	}

	public function hasStreamingReplicaServers() {
	return $this->serverInfo->hasStreamingReplicaServers();
	}

	public function getServerName( $i ): string {
	return $this->serverInfo->getServerName( $i );
	}

	public function getServerInfo( $i ) {
	return $this->serverInfo->getServerInfo( $i );
	}

	public function getServerType( $i ) {
	return $this->serverInfo->getServerType( $i );
	}

	public function getPrimaryPos() {
	$conn = $this->getAnyOpenConnection( ServerInfo::WRITER_INDEX );
	if ( $conn ) {
	return $conn->getPrimaryPos();
	}

	$conn = $this->getConnectionInternal( ServerInfo::WRITER_INDEX, self::CONN_SILENCE_ERRORS );
	// @phan-suppress-next-line PhanRedundantCondition
	if ( !$conn ) {
	$this->reportConnectionError();
	}

	// ::getConnectionInternal() should return IDatabaseForOwner but changing signature
	// is not straightforward (being implemented in Wikibase)
	'@phan-var IDatabaseForOwner $conn';
	try {
	return $conn->getPrimaryPos();
	} finally {
	$this->closeConnection( $conn );
	}
	}

	/**
	* Apply updated configuration.
	*
	* This only unregisters servers that were removed in the new configuration.
	* It does not register new servers nor update the group load weights.
	*
	* This invalidates any open connections. However, existing connections may continue to be
	* used while they are in an active transaction. In that case, the old connection will be
	* discarded on the first operation after the transaction is complete. The next operation
	* will use a new connection based on the new configuration.
	*
	* @internal for use by LBFactory::reconfigure()
	*
	* @see DBConnRef::ensureConnection()
	* @see LBFactory::reconfigure()
	*
	* @param array $params A database configuration array, see $wgLBFactoryConf.
	*
	* @return void
	*/
	public function reconfigure( array $params ) {
	$anyServerDepooled = false;

	$paramServers = $params['servers'];
	$newIndexByServerIndex = $this->serverInfo->reconfigureServers( $paramServers );
	foreach ( $newIndexByServerIndex as $i => $ni ) {
	if ( $ni !== null ) {
	// Server still exists in the new config
	$newWeightByGroup = $paramServers[$ni]['groupLoads'] ?? [];
	$newWeightByGroup[ILoadBalancer::GROUP_GENERIC] = $paramServers[$ni]['load'];
	// Check if the server was removed from any load groups
	foreach ( $this->groupLoads as $group => $weightByIndex ) {
	if ( isset( $weightByIndex[$i] ) && !isset( $newWeightByGroup[$group] ) ) {
	// Server no longer in this load group in the new config
	$anyServerDepooled = true;
	unset( $this->groupLoads[$group][$i] );
	}
	}
	} else {
	// Server no longer exists in the new config
	$anyServerDepooled = true;
	// Note that if the primary server is depooled and a replica server promoted
	// to new primary, then DB_PRIMARY handles will fail with server index errors
	foreach ( $this->groupLoads as $group => $loads ) {
	unset( $this->groupLoads[$group][$i] );
	}
	}
	}

	if ( $anyServerDepooled ) {
	// NOTE: We could close all connection here, but some may be in the middle of
	// a transaction. So instead, we leave it to DBConnRef to close the
	// connection when it detects that the modcount has changed and no
	// transaction is open.
	$this->logger->info( 'Reconfiguring dbs!' );
	// Unpin DB_REPLICA connection groups from server indexes
	$this->readIndexByGroup = [];
	// We could close all connection here, but some may be in the middle of a
	// transaction. So instead, we leave it to DBConnRef to close the connection
	// when it detects that the modcount has changed and no transaction is open.
	$this->conns = self::newTrackedConnectionsArray();
	// Bump modification counter to invalidate the connections held by DBConnRef
	// instances. This will cause the next call to a method on the DBConnRef
	// to get a new connection from getConnectionInternal()
	$this->modcount++;
	}
	}

	public function disable( $fname = __METHOD__ ) {
	$this->closeAll( $fname );
	$this->disabled = true;
	}

	public function closeAll( $fname = __METHOD__ ) {
	/** @noinspection PhpUnusedLocalVariableInspection */
	$scope = ScopedCallback::newScopedIgnoreUserAbort();
	foreach ( $this->getOpenConnections() as $conn ) {
	$conn->close( $fname );
	}

	$this->conns = self::newTrackedConnectionsArray();
	}

	/**
	* Close a connection
	*
	* Using this function makes sure the LoadBalancer knows the connection is closed.
	* If you use $conn->close() directly, the load balancer won't update its state.
	*
	* @param IDatabaseForOwner $conn
	*/
	private function closeConnection( IDatabaseForOwner $conn ) {
	if ( $conn instanceof DBConnRef ) {
	// Avoid calling close() but still leaving the handle in the pool
	throw new RuntimeException( 'Cannot close DBConnRef instance; it must be shareable' );
	}

	$domain = $conn->getDomainID();
	$serverIndex = $conn->getLBInfo( self::INFO_SERVER_INDEX );
	if ( $serverIndex === null ) {
	throw new UnexpectedValueException( "Handle on '$domain' missing server index" );
	}

	$srvName = $this->serverInfo->getServerName( $serverIndex );

	$found = false;
	foreach ( $this->conns as $type => $poolConnsByServer ) {
	$key = array_search( $conn, $poolConnsByServer[$serverIndex] ?? [], true );
	if ( $key !== false ) {
	$found = true;
	unset( $this->conns[$type][$serverIndex][$key] );
	}
	}

	if ( !$found ) {
	$this->logger->warning(
	__METHOD__ .
	": orphaned connection to database {$this->stringifyConn( $conn )} at '$srvName'."
	);
	}

	$this->logger->debug(
	__METHOD__ .
	": closing connection to database {$this->stringifyConn( $conn )} at '$srvName'."
	);

	$conn->close( __METHOD__ );
	}

	public function finalizePrimaryChanges( $fname = __METHOD__ ) {
	$this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
	/** @noinspection PhpUnusedLocalVariableInspection */
	$scope = ScopedCallback::newScopedIgnoreUserAbort();

	$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
	// Loop until callbacks stop adding callbacks on other connections
	$total = 0;
	do {
	$count = 0; // callbacks execution attempts
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	// Run any pre-commit callbacks while leaving the post-commit ones suppressed.
	// Any error should cause all (peer) transactions to be rolled back together.
	$count += $conn->runOnTransactionPreCommitCallbacks();
	}
	$total += $count;
	} while ( $count > 0 );
	// Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$conn->setTrxEndCallbackSuppression( true );
	}
	$this->trxRoundStage = self::ROUND_FINALIZED;

	return $total;
	}

	public function approvePrimaryChanges( int $maxWriteDuration, $fname = __METHOD__ ) {
	$this->assertTransactionRoundStage( self::ROUND_FINALIZED );
	/** @noinspection PhpUnusedLocalVariableInspection */
	$scope = ScopedCallback::newScopedIgnoreUserAbort();

	$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	// Any atomic sections should have been closed by now and there definitely should
	// not be any open transactions started by begin() from callers outside Database.
	if ( $conn->explicitTrxActive() ) {
	throw new DBTransactionError(
	$conn,
	"Explicit transaction still active; a caller might have failed to call " .
	"endAtomic() or cancelAtomic()."
	);
	}
	// Assert that the time to replicate the transaction will be reasonable.
	// If this fails, then all DB transactions will be rollback back together.
	$time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
	if ( $maxWriteDuration > 0 ) {
	if ( $time > $maxWriteDuration ) {
	$humanTimeSec = round( $time, 3 );
	throw new DBTransactionSizeError(
	$conn,
	"Transaction spent {time}s in writes, exceeding the {$maxWriteDuration}s limit",
	// Message parameters for: transaction-duration-limit-exceeded
	[ $time, $maxWriteDuration ],
	null,
	[ 'time' => $humanTimeSec ]
	);
	} elseif ( $time > 0 ) {
	$timeMs = $time * 1000;
	$humanTimeMs = round( $timeMs, $timeMs > 1 ? 0 : 3 );
	$this->logger->debug(
	"Transaction spent {time_ms}ms in writes, under the {$maxWriteDuration}s limit",
	[ 'time_ms' => $humanTimeMs ]
	);
	}
	}
	// If a connection sits idle for too long it might be dropped, causing transaction
	// writes and session locks to be lost. Ping all the server connections before making
	// any attempt to commit the transactions belonging to the active transaction round.
	if ( $conn->writesOrCallbacksPending() \|\| $conn->sessionLocksPending() ) {
	if ( !$conn->ping() ) {
	throw new DBTransactionError(
	$conn,
	"Pre-commit ping failed on server {$conn->getServerName()}"
	);
	}
	}
	}
	$this->trxRoundStage = self::ROUND_APPROVED;
	}

	public function beginPrimaryChanges( $fname = __METHOD__ ) {
	if ( $this->trxRoundId !== false ) {
	throw new DBTransactionError(
	null,
	"Transaction round '{$this->trxRoundId}' already started"
	);
	}
	$this->assertTransactionRoundStage( self::ROUND_CURSORY );
	/** @noinspection PhpUnusedLocalVariableInspection */
	$scope = ScopedCallback::newScopedIgnoreUserAbort();

	// Clear any empty transactions (no writes/callbacks) from the implicit round
	$this->flushPrimarySnapshots( $fname );

	$this->trxRoundId = $fname;
	$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
	// Mark applicable handles as participating in this explicit transaction round.
	// For each of these handles, any writes and callbacks will be tied to a single
	// transaction. The (peer) handles will reject begin()/commit() calls unless they
	// are part of an en masse commit or an en masse rollback.
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$this->applyTransactionRoundFlags( $conn );
	}
	$this->trxRoundStage = self::ROUND_CURSORY;
	}

	public function commitPrimaryChanges( $fname = __METHOD__ ) {
	$this->assertTransactionRoundStage( self::ROUND_APPROVED );
	/** @noinspection PhpUnusedLocalVariableInspection */
	$scope = ScopedCallback::newScopedIgnoreUserAbort();

	$failures = [];

	$restore = ( $this->trxRoundId !== false );
	$this->trxRoundId = false;
	$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
	// Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
	// Note that callbacks should already be suppressed due to finalizePrimaryChanges().
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	try {
	$conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
	} catch ( DBError $e ) {
	( $this->errorLogger )( $e );
	$failures[] = "{$conn->getServerName()}: {$e->getMessage()}";
	}
	}
	if ( $failures ) {
	throw new DBTransactionError(
	null,
	"Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
	);
	}
	if ( $restore ) {
	// Unmark handles as participating in this explicit transaction round
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$this->undoTransactionRoundFlags( $conn );
	}
	}
	$this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
	}

	public function runPrimaryTransactionIdleCallbacks( $fname = __METHOD__ ) {
	if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
	$type = IDatabase::TRIGGER_COMMIT;
	} elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
	$type = IDatabase::TRIGGER_ROLLBACK;
	} else {
	throw new DBTransactionError(
	null,
	"Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
	);
	}
	/** @noinspection PhpUnusedLocalVariableInspection */
	$scope = ScopedCallback::newScopedIgnoreUserAbort();

	$oldStage = $this->trxRoundStage;
	$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise

	// Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$conn->setTrxEndCallbackSuppression( false );
	}

	$errors = [];
	$fname = __METHOD__;
	// Loop until callbacks stop adding callbacks on other connections
	do {
	// Run any pending callbacks for each connection...
	$count = 0; // callback execution attempts
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	if ( $conn->trxLevel() ) {
	continue; // retry in the next iteration, after commit() is called
	}
	$count += $conn->runOnTransactionIdleCallbacks( $type, $errors );
	}
	// Clear out any active transactions left over from callbacks...
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	if ( $conn->writesPending() ) {
	// A callback from another handle wrote to this one and DBO_TRX is set
	$fnames = implode( ', ', $conn->pendingWriteCallers() );
	$this->logger->info(
	"$fname: found writes pending ($fnames).",
	$this->getConnLogContext(
	$conn,
	[ 'exception' => new RuntimeException() ]
	)
	);
	} elseif ( $conn->trxLevel() ) {
	// A callback from another handle read from this one and DBO_TRX is set,
	// which can easily happen if there is only one DB (no replicas)
	$this->logger->debug( "$fname: found empty transaction." );
	}
	try {
	$conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
	} catch ( DBError $ex ) {
	$errors[] = $ex;
	}
	}
	} while ( $count > 0 );

	$this->trxRoundStage = $oldStage;

	return $errors[0] ?? null;
	}

	public function runPrimaryTransactionListenerCallbacks( $fname = __METHOD__ ) {
	if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
	$type = IDatabase::TRIGGER_COMMIT;
	} elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
	$type = IDatabase::TRIGGER_ROLLBACK;
	} else {
	throw new DBTransactionError(
	null,
	"Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
	);
	}
	/** @noinspection PhpUnusedLocalVariableInspection */
	$scope = ScopedCallback::newScopedIgnoreUserAbort();

	$errors = [];
	$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$conn->runTransactionListenerCallbacks( $type, $errors );
	}
	$this->trxRoundStage = self::ROUND_CURSORY;

	return $errors[0] ?? null;
	}

	public function rollbackPrimaryChanges( $fname = __METHOD__ ) {
	/** @noinspection PhpUnusedLocalVariableInspection */
	$scope = ScopedCallback::newScopedIgnoreUserAbort();

	$restore = ( $this->trxRoundId !== false );
	$this->trxRoundId = false;
	$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
	}
	if ( $restore ) {
	// Unmark handles as participating in this explicit transaction round
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$this->undoTransactionRoundFlags( $conn );
	}
	}
	$this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
	}

	public function flushPrimarySessions( $fname = __METHOD__ ) {
	$this->assertTransactionRoundStage( [ self::ROUND_CURSORY ] );
	if ( $this->hasPrimaryChanges() ) {
	// Any transaction should have been rolled back beforehand
	throw new DBTransactionError( null, "Cannot reset session while writes are pending" );
	}

	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$conn->flushSession( $fname, $conn::FLUSHING_ALL_PEERS );
	}
	}

	/**
	* @param string\|string[] $stage
	* @throws DBTransactionError
	*/
	private function assertTransactionRoundStage( $stage ) {
	$stages = (array)$stage;

	if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
	$stageList = implode(
	'/',
	array_map( static function ( $v ) {
	return "'$v'";
	}, $stages )
	);
	throw new DBTransactionError(
	null,
	"Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
	);
	}
	}

	/**
	* Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
	*
	* Some servers may have neither flag enabled, meaning that they opt out of such
	* transaction rounds and remain in auto-commit mode. Such behavior might be desired
	* when a DB server is used for something like simple key/value storage.
	*
	* @param Database $conn
	*/
	private function applyTransactionRoundFlags( Database $conn ) {
	if ( $conn->getLBInfo( self::INFO_CONN_CATEGORY ) !== self::CATEGORY_ROUND ) {
	return; // transaction rounds do not apply to these connections
	}

	if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
	// DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
	// Force DBO_TRX even in CLI mode since a commit round is expected soon.
	$conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
	}

	if ( $conn->getFlag( $conn::DBO_TRX ) ) {
	$conn->setLBInfo( $conn::LB_TRX_ROUND_ID, $this->trxRoundId );
	}
	}

	/**
	* @param Database $conn
	*/
	private function undoTransactionRoundFlags( Database $conn ) {
	if ( $conn->getLBInfo( self::INFO_CONN_CATEGORY ) !== self::CATEGORY_ROUND ) {
	return; // transaction rounds do not apply to these connections
	}

	if ( $conn->getFlag( $conn::DBO_TRX ) ) {
	$conn->setLBInfo( $conn::LB_TRX_ROUND_ID, null ); // remove the round ID
	}

	if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
	$conn->restoreFlags( $conn::RESTORE_PRIOR );
	}
	}

	public function flushReplicaSnapshots( $fname = __METHOD__ ) {
	foreach ( $this->conns as $poolConnsByServer ) {
	foreach ( $poolConnsByServer as $serverIndex => $serverConns ) {
	if ( $serverIndex === ServerInfo::WRITER_INDEX ) {
	continue; // skip primary
	}
	foreach ( $serverConns as $conn ) {
	$conn->flushSnapshot( $fname );
	}
	}
	}
	}

	public function flushPrimarySnapshots( $fname = __METHOD__ ) {
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$conn->flushSnapshot( $fname );
	}
	}

	public function hasPrimaryConnection() {
	return (bool)$this->getAnyOpenConnection( ServerInfo::WRITER_INDEX );
	}

	public function hasPrimaryChanges() {
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	if ( $conn->writesOrCallbacksPending() ) {
	return true;
	}
	}

	return false;
	}

	public function lastPrimaryChangeTimestamp() {
	$lastTime = false;
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$lastTime = max( $lastTime, $conn->lastDoneWrites() );
	}

	return $lastTime;
	}

	public function hasOrMadeRecentPrimaryChanges( $age = null ) {
	$age ??= self::MAX_WAIT_DEFAULT;

	return ( $this->hasPrimaryChanges()
	\|\| $this->lastPrimaryChangeTimestamp() > microtime( true ) - $age );
	}

	public function pendingPrimaryChangeCallers() {
	$fnames = [];
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
	}

	return $fnames;
	}

	public function explicitTrxActive() {
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	if ( $conn->explicitTrxActive() ) {
	return true;
	}
	}
	return false;
	}

	private function setLaggedReplicaMode(): void {
	$this->laggedReplicaMode = true;
	$this->logger->warning( __METHOD__ . ": setting lagged replica mode" );
	}

	public function laggedReplicaUsed() {
	return $this->laggedReplicaMode;
	}

	public function getReadOnlyReason() {
	if ( $this->readOnlyReason !== false ) {
	return $this->readOnlyReason;
	} elseif ( $this->isPrimaryRunningReadOnly() ) {
	return 'The primary database server is running in read-only mode.';
	}

	return false;
	}

	/**
	* @note This method suppresses DBError exceptions in order to avoid severe downtime
	* @param IDatabaseForOwner\|null $conn Recently acquired primary connection; null if not applicable
	* @return bool Whether the entire primary DB server or the local domain DB is read-only
	*/
	private function isPrimaryRunningReadOnly( ?IDatabaseForOwner $conn = null ) {
	// Context will often be HTTP GET/HEAD; heavily cache the results
	return (bool)$this->wanCache->getWithSetCallback(
	// Note that table prefixes are not related to server-side read-only mode
	$this->wanCache->makeGlobalKey(
	'rdbms-server-readonly',
	$this->serverInfo->getPrimaryServerName()
	),
	self::TTL_CACHE_READONLY,
	function ( $oldValue ) use ( $conn ) {
	$scope = $this->trxProfiler->silenceForScope();
	$conn ??= $this->getServerConnection(
	ServerInfo::WRITER_INDEX,
	self::DOMAIN_ANY,
	self::CONN_SILENCE_ERRORS
	);
	if ( $conn ) {
	try {
	$value = (int)$conn->serverIsReadOnly();
	} catch ( DBError $e ) {
	$value = is_int( $oldValue ) ? $oldValue : 0;
	}
	} else {
	$value = 0;
	}
	ScopedCallback::consume( $scope );

	return $value;
	},
	[
	'busyValue' => 0,
	'pcTTL' => WANObjectCache::TTL_PROC_LONG
	]
	);
	}

	public function pingAll() {
	$success = true;
	foreach ( $this->getOpenConnections() as $conn ) {
	if ( !$conn->ping() ) {
	$success = false;
	}
	}

	return $success;
	}

	/**
	* Get all open connections
	* @return \Generator\|Database[]
	*/
	private function getOpenConnections() {
	foreach ( $this->conns as $poolConnsByServer ) {
	foreach ( $poolConnsByServer as $serverConns ) {
	foreach ( $serverConns as $conn ) {
	yield $conn;
	}
	}
	}
	}

	/**
	* Get all open primary connections
	* @return \Generator\|Database[]
	*/
	private function getOpenPrimaryConnections() {
	foreach ( $this->conns as $poolConnsByServer ) {
	/** @var IDatabaseForOwner $conn */
	foreach ( ( $poolConnsByServer[ServerInfo::WRITER_INDEX] ?? [] ) as $conn ) {
	yield $conn;
	}
	}
	}

	public function getMaxLag() {
	$host = '';
	$maxLag = -1;
	$maxIndex = 0;

	if ( $this->serverInfo->hasReplicaServers() ) {
	$lagTimes = $this->getLagTimes();
	foreach ( $lagTimes as $i => $lag ) {
	// Allowing the value to be unset due to stale cache (T361824)
	$load = $this->groupLoads[self::GROUP_GENERIC][$i] ?? 0;
	if ( $load > 0 && $lag > $maxLag ) {
	$maxLag = $lag;
	$host = $this->serverInfo->getServerInfoStrict( $i, 'host' );
	$maxIndex = $i;
	}
	}
	}

	return [ $host, $maxLag, $maxIndex ];
	}

	public function getLagTimes() {
	if ( !$this->hasReplicaServers() ) {
	return [ ServerInfo::WRITER_INDEX => 0 ]; // no replication = no lag
	}
	$fname = __METHOD__;
	return $this->wanCache->getWithSetCallback(
	$this->wanCache->makeGlobalKey( 'rdbms-lags', $this->getClusterName() ),
	// Add jitter to avoid stampede
	10 + mt_rand( 1, 10 ),
	function () use ( $fname ) {
	$lags = [];
	foreach ( $this->serverInfo->getStreamingReplicaIndexes() as $i ) {
	$conn = $this->getServerConnection(
	$i,
	self::DOMAIN_ANY,
	self::CONN_SILENCE_ERRORS \| self::CONN_UNTRACKED_GAUGE
	);
	if ( $conn ) {
	$lags[$i] = $conn->getLag();
	$conn->close( $fname );
	} else {
	$lags[$i] = false;
	}
	}
	return $lags;
	},
	[ 'lockTSE' => 30 ]
	);
	}

	public function waitForPrimaryPos( IDatabase $conn ) {
	if ( $conn->getLBInfo( self::INFO_SERVER_INDEX ) === ServerInfo::WRITER_INDEX ) {
	return true; // not a replica DB server
	}

	// Get the current primary DB position, opening a connection only if needed
	$flags = self::CONN_SILENCE_ERRORS;
	$primaryConn = $this->getAnyOpenConnection( ServerInfo::WRITER_INDEX, $flags );
	if ( $primaryConn ) {
	$pos = $primaryConn->getPrimaryPos();
	} else {
	$primaryConn = $this->getServerConnection( ServerInfo::WRITER_INDEX, self::DOMAIN_ANY, $flags );
	if ( !$primaryConn ) {
	throw new DBReplicationWaitError(
	null,
	"Could not obtain a primary database connection to get the position"
	);
	}
	$pos = $primaryConn->getPrimaryPos();
	$this->closeConnection( $primaryConn );
	}

	if ( $pos instanceof DBPrimaryPos && $conn instanceof IDatabaseForOwner ) {
	$this->logger->debug( __METHOD__ . ': waiting' );
	$result = $conn->primaryPosWait( $pos, self::MAX_WAIT_DEFAULT );
	$ok = ( $result !== null && $result != -1 );
	if ( $ok ) {
	$this->logger->debug( __METHOD__ . ': done waiting (success)' );
	} else {
	$this->logger->debug( __METHOD__ . ': done waiting (failure)' );
	}
	} else {
	$ok = false; // something is misconfigured
	$this->logger->error(
	__METHOD__ . ': could not get primary pos for {db_server}',
	$this->getConnLogContext( $conn, [ 'exception' => new RuntimeException() ] )
	);
	}

	return $ok;
	}

	public function setTransactionListener( $name, ?callable $callback = null ) {
	if ( $callback ) {
	$this->trxRecurringCallbacks[$name] = $callback;
	} else {
	unset( $this->trxRecurringCallbacks[$name] );
	}
	foreach ( $this->getOpenPrimaryConnections() as $conn ) {
	$conn->setTransactionListener( $name, $callback );
	}
	}

	public function setTableAliases( array $aliases ) {
	$this->tableAliases = $aliases;
	}

	public function setIndexAliases( array $aliases ) {
	$this->indexAliases = $aliases;
	}

	public function setDomainAliases( array $aliases ) {
	$this->domainAliases = $aliases;
	}

	public function setLocalDomainPrefix( $prefix ) {
	$oldLocalDomain = $this->localDomain;
	$this->localDomain = new DatabaseDomain(
	$this->localDomain->getDatabase(),
	$this->localDomain->getSchema(),
	$prefix
	);

	// Update the prefix for existing connections.
	// Existing DBConnRef handles will not be affected.
	foreach ( $this->getOpenConnections() as $conn ) {
	if ( $oldLocalDomain->equals( $conn->getDomainID() ) ) {
	$conn->tablePrefix( $prefix );
	}
	}
	}

	public function redefineLocalDomain( $domain ) {
	$this->closeAll( __METHOD__ );
	$this->localDomain = DatabaseDomain::newFromId( $domain );
	}

	public function setTempTablesOnlyMode( $value, $domain ) {
	$old = $this->tempTablesOnlyMode[$domain] ?? false;
	if ( $value ) {
	$this->tempTablesOnlyMode[$domain] = true;
	} else {
	unset( $this->tempTablesOnlyMode[$domain] );
	}

	return $old;
	}

	/**
	* @param IDatabase $conn
	* @return string Description of a connection handle for log messages
	* @throws InvalidArgumentException
	*/
	private function stringifyConn( IDatabase $conn ) {
	return $conn->getLBInfo( self::INFO_SERVER_INDEX ) . '/' . $conn->getDomainID();
	}

	/**
	* @param int $flags A bitfield of flags
	* @param int $bit Bit flag constant
	* @return bool Whether the bit field has the specified bit flag set
	*/
	private function fieldHasBit( int $flags, int $bit ) {
	return ( ( $flags & $bit ) === $bit );
	}

	/**
	* Create a log context to pass to PSR-3 logger functions.
	*
	* @param IDatabase $conn
	* @param array $extras Additional data to add to context
	* @return array
	*/
	protected function getConnLogContext( IDatabase $conn, array $extras = [] ) {
	return array_merge(
	[
	'db_server' => $conn->getServerName(),
	'db_domain' => $conn->getDomainID()
	],
	$extras
	);
	}

	/**
	* @param float\|null &$time Mock UNIX timestamp for testing
	* @internal
	* @codeCoverageIgnore
	*/
	public function setMockTime( &$time ) {
	$this->loadMonitor->setMockTime( $time );
	}
	}

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