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| 1 | <?php |
| 2 | /** |
| 3 | * This program is free software; you can redistribute it and/or modify |
| 4 | * it under the terms of the GNU General Public License as published by |
| 5 | * the Free Software Foundation; either version 2 of the License, or |
| 6 | * (at your option) any later version. |
| 7 | * |
| 8 | * This program is distributed in the hope that it will be useful, |
| 9 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 10 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 11 | * GNU General Public License for more details. |
| 12 | * |
| 13 | * You should have received a copy of the GNU General Public License along |
| 14 | * with this program; if not, write to the Free Software Foundation, Inc., |
| 15 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. |
| 16 | * http://www.gnu.org/copyleft/gpl.html |
| 17 | * |
| 18 | * @file |
| 19 | */ |
| 20 | namespace Wikimedia\Rdbms\Replication; |
| 21 | |
| 22 | use Psr\Log\LoggerInterface; |
| 23 | use Wikimedia\ObjectCache\BagOStuff; |
| 24 | use Wikimedia\Rdbms\DBError; |
| 25 | use Wikimedia\Rdbms\DBPrimaryPos; |
| 26 | use Wikimedia\Rdbms\IDatabase; |
| 27 | |
| 28 | /** |
| 29 | * @internal |
| 30 | * @ingroup Database |
| 31 | * @since 1.40 |
| 32 | */ |
| 33 | class ReplicationReporter { |
| 34 | /** @var string Replication topology role of the server; one of the class ROLE_* constants */ |
| 35 | protected $topologyRole; |
| 36 | /** @var LoggerInterface */ |
| 37 | protected $logger; |
| 38 | /** @var BagOStuff */ |
| 39 | protected $srvCache; |
| 40 | /** @var array|null Replication lag estimate at the time of BEGIN for the last transaction */ |
| 41 | private $trxReplicaLagStatus = null; |
| 42 | |
| 43 | public function __construct( $topologyRole, $logger, $srvCache ) { |
| 44 | $this->topologyRole = $topologyRole; |
| 45 | $this->logger = $logger; |
| 46 | $this->srvCache = $srvCache; |
| 47 | } |
| 48 | |
| 49 | public function getTopologyRole() { |
| 50 | return $this->topologyRole; |
| 51 | } |
| 52 | |
| 53 | public function getLag( IDatabase $conn ) { |
| 54 | if ( $this->topologyRole === IDatabase::ROLE_STREAMING_MASTER ) { |
| 55 | return 0; // this is the primary DB |
| 56 | } elseif ( $this->topologyRole === IDatabase::ROLE_STATIC_CLONE ) { |
| 57 | return 0; // static dataset |
| 58 | } |
| 59 | |
| 60 | return $this->doGetLag( $conn ); |
| 61 | } |
| 62 | |
| 63 | /** |
| 64 | * Get the amount of replication lag for this database server |
| 65 | * |
| 66 | * Callers should avoid using this method while a transaction is active |
| 67 | * |
| 68 | * @see getLag() |
| 69 | * |
| 70 | * @param IDatabase $conn To make queries |
| 71 | * @return float|int|false Database replication lag in seconds or false on error |
| 72 | * @throws DBError |
| 73 | */ |
| 74 | protected function doGetLag( IDatabase $conn ) { |
| 75 | return 0; |
| 76 | } |
| 77 | |
| 78 | /** |
| 79 | * Get a replica DB lag estimate for this server at the start of a transaction |
| 80 | * |
| 81 | * This is a no-op unless the server is known a priori to be a replica DB |
| 82 | * |
| 83 | * @param IDatabase $conn To make queries |
| 84 | * @return array ('lag': seconds or false on error, 'since': UNIX timestamp of estimate) |
| 85 | * @since 1.27 in Database, moved to ReplicationReporter in 1.40 |
| 86 | */ |
| 87 | protected function getApproximateLagStatus( IDatabase $conn ) { |
| 88 | if ( $this->topologyRole === IDatabase::ROLE_STREAMING_REPLICA ) { |
| 89 | // Avoid exceptions as this is used internally in critical sections |
| 90 | try { |
| 91 | $lag = $this->getLag( $conn ); |
| 92 | } catch ( DBError $e ) { |
| 93 | $lag = false; |
| 94 | } |
| 95 | } else { |
| 96 | $lag = 0; |
| 97 | } |
| 98 | |
| 99 | return [ 'lag' => $lag, 'since' => microtime( true ) ]; |
| 100 | } |
| 101 | |
| 102 | public function primaryPosWait( IDatabase $conn, DBPrimaryPos $pos, $timeout ) { |
| 103 | // Real waits are implemented in the subclass. |
| 104 | return 0; |
| 105 | } |
| 106 | |
| 107 | public function getReplicaPos( IDatabase $conn ) { |
| 108 | // Stub |
| 109 | return false; |
| 110 | } |
| 111 | |
| 112 | public function getPrimaryPos( IDatabase $conn ) { |
| 113 | // Stub |
| 114 | return false; |
| 115 | } |
| 116 | |
| 117 | /** |
| 118 | * @return array|null Tuple of (reason string, "role") if read-only; null otherwise |
| 119 | */ |
| 120 | public function getTopologyBasedReadOnlyReason() { |
| 121 | if ( $this->topologyRole === IDatabase::ROLE_STREAMING_REPLICA ) { |
| 122 | return [ 'Server is configured as a read-only replica database.', 'role' ]; |
| 123 | } elseif ( $this->topologyRole === IDatabase::ROLE_STATIC_CLONE ) { |
| 124 | return [ 'Server is configured as a read-only static clone database.', 'role' ]; |
| 125 | } |
| 126 | |
| 127 | return null; |
| 128 | } |
| 129 | |
| 130 | public function resetReplicationLagStatus( IDatabase $conn ) { |
| 131 | // With REPEATABLE-READ isolation, the first SELECT establishes the read snapshot, |
| 132 | // so get the replication lag estimate before any transaction SELECT queries come in. |
| 133 | // This way, the lag estimate reflects what will actually be read. Also, if heartbeat |
| 134 | // tables are used, this avoids counting snapshot lag as part of replication lag. |
| 135 | $this->trxReplicaLagStatus = null; // clear cached value first |
| 136 | $this->trxReplicaLagStatus = $this->getApproximateLagStatus( $conn ); |
| 137 | } |
| 138 | |
| 139 | /** |
| 140 | * Get the replica DB lag when the current transaction started |
| 141 | * |
| 142 | * This is useful given that transactions might use point-in-time read snapshots, |
| 143 | * in which case the lag estimate should be recorded just before the transaction |
| 144 | * establishes the read snapshot (either BEGIN or the first SELECT/write query). |
| 145 | * |
| 146 | * If snapshots are not used, it is still safe to be pessimistic. |
| 147 | * |
| 148 | * This returns null if there is no transaction or the lag status was not yet recorded. |
| 149 | * |
| 150 | * @param IDatabase $conn To make queries |
| 151 | * @return array|null ('lag': seconds or false, 'since': UNIX timestamp of BEGIN) or null |
| 152 | * @since 1.27 in Database, moved to ReplicationReporter in 1.40 |
| 153 | */ |
| 154 | final protected function getRecordedTransactionLagStatus( IDatabase $conn ) { |
| 155 | return $conn->trxLevel() ? $this->trxReplicaLagStatus : null; |
| 156 | } |
| 157 | |
| 158 | public function getSessionLagStatus( IDatabase $conn ) { |
| 159 | return $this->getRecordedTransactionLagStatus( $conn ) ?: $this->getApproximateLagStatus( $conn ); |
| 160 | } |
| 161 | |
| 162 | /** |
| 163 | * Create a log context to pass to PSR-3 logger functions. |
| 164 | * |
| 165 | * @param IDatabase $conn To make queries |
| 166 | * @param array $extras Additional data to add to context |
| 167 | * @return array |
| 168 | */ |
| 169 | protected function getLogContext( IDatabase $conn, array $extras = [] ) { |
| 170 | return array_merge( |
| 171 | [ |
| 172 | 'db_server' => $conn->getServerName(), |
| 173 | 'db_name' => $conn->getDBname(), |
| 174 | // TODO: Add db_user |
| 175 | ], |
| 176 | $extras |
| 177 | ); |
| 178 | } |
| 179 | } |