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ReplicationReporter.php
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ReplicationReporter.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\Replication;
use Psr\Log\LoggerInterface;
use Wikimedia\ObjectCache\BagOStuff;
use Wikimedia\Rdbms\DBError;
use Wikimedia\Rdbms\DBPrimaryPos;
use Wikimedia\Rdbms\IDatabase;
/**
* @internal
* @ingroup Database
* @since 1.40
*/
class ReplicationReporter {
/** @var string Replication topology role of the server; one of the class ROLE_* constants */
protected $topologyRole;
/** @var LoggerInterface */
protected $logger;
/** @var BagOStuff */
protected $srvCache;
/** @var array|null Replication lag estimate at the time of BEGIN for the last transaction */
private $trxReplicaLagStatus = null;
public function __construct( $topologyRole, $logger, $srvCache ) {
$this->topologyRole = $topologyRole;
$this->logger = $logger;
$this->srvCache = $srvCache;
}
public function getTopologyRole() {
return $this->topologyRole;
}
public function getLag( IDatabase $conn ) {
if ( $this->topologyRole === IDatabase::ROLE_STREAMING_MASTER ) {
return 0; // this is the primary DB
} elseif ( $this->topologyRole === IDatabase::ROLE_STATIC_CLONE ) {
return 0; // static dataset
}
return $this->doGetLag( $conn );
}
/**
* Get the amount of replication lag for this database server
*
* Callers should avoid using this method while a transaction is active
*
* @see getLag()
*
* @param IDatabase $conn To make queries
* @return float|int|false Database replication lag in seconds or false on error
* @throws DBError
*/
protected function doGetLag( IDatabase $conn ) {
return 0;
}
/**
* Get a replica DB lag estimate for this server at the start of a transaction
*
* This is a no-op unless the server is known a priori to be a replica DB
*
* @param IDatabase $conn To make queries
* @return array ('lag': seconds or false on error, 'since': UNIX timestamp of estimate)
* @since 1.27 in Database, moved to ReplicationReporter in 1.40
*/
protected function getApproximateLagStatus( IDatabase $conn ) {
if ( $this->topologyRole === IDatabase::ROLE_STREAMING_REPLICA ) {
// Avoid exceptions as this is used internally in critical sections
try {
$lag = $this->getLag( $conn );
} catch ( DBError $e ) {
$lag = false;
}
} else {
$lag = 0;
}
return [ 'lag' => $lag, 'since' => microtime( true ) ];
}
public function primaryPosWait( IDatabase $conn, DBPrimaryPos $pos, $timeout ) {
// Real waits are implemented in the subclass.
return 0;
}
public function getReplicaPos( IDatabase $conn ) {
// Stub
return false;
}
public function getPrimaryPos( IDatabase $conn ) {
// Stub
return false;
}
/**
* @return array|null Tuple of (reason string, "role") if read-only; null otherwise
*/
public function getTopologyBasedReadOnlyReason() {
if ( $this->topologyRole === IDatabase::ROLE_STREAMING_REPLICA ) {
return [ 'Server is configured as a read-only replica database.', 'role' ];
} elseif ( $this->topologyRole === IDatabase::ROLE_STATIC_CLONE ) {
return [ 'Server is configured as a read-only static clone database.', 'role' ];
}
return null;
}
public function resetReplicationLagStatus( IDatabase $conn ) {
// With REPEATABLE-READ isolation, the first SELECT establishes the read snapshot,
// so get the replication lag estimate before any transaction SELECT queries come in.
// This way, the lag estimate reflects what will actually be read. Also, if heartbeat
// tables are used, this avoids counting snapshot lag as part of replication lag.
$this->trxReplicaLagStatus = null; // clear cached value first
$this->trxReplicaLagStatus = $this->getApproximateLagStatus( $conn );
}
/**
* Get the replica DB lag when the current transaction started
*
* This is useful given that transactions might use point-in-time read snapshots,
* in which case the lag estimate should be recorded just before the transaction
* establishes the read snapshot (either BEGIN or the first SELECT/write query).
*
* If snapshots are not used, it is still safe to be pessimistic.
*
* This returns null if there is no transaction or the lag status was not yet recorded.
*
* @param IDatabase $conn To make queries
* @return array|null ('lag': seconds or false, 'since': UNIX timestamp of BEGIN) or null
* @since 1.27 in Database, moved to ReplicationReporter in 1.40
*/
final protected function getRecordedTransactionLagStatus( IDatabase $conn ) {
return $conn->trxLevel() ? $this->trxReplicaLagStatus : null;
}
public function getSessionLagStatus( IDatabase $conn ) {
return $this->getRecordedTransactionLagStatus( $conn ) ?: $this->getApproximateLagStatus( $conn );
}
/**
* Create a log context to pass to PSR-3 logger functions.
*
* @param IDatabase $conn To make queries
* @param array $extras Additional data to add to context
* @return array
*/
protected function getLogContext( IDatabase $conn, array $extras = [] ) {
return array_merge(
[
'db_server' => $conn->getServerName(),
'db_name' => $conn->getDBname(),
// TODO: Add db_user
],
$extras
);
}
}

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ReplicationReporter.php (5 KB)

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