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Duplicate code is one of the most pungent code smells. A rule that is often used is to re-structure code once it is duplicated in three or more places.
Common duplication problems, and corresponding solutions are:
Complex classes like LoadBalancer often do a lot of different things. To break such a class down, we need to identify a cohesive component within that class. A common approach to find such a component is to look for fields/methods that share the same prefixes, or suffixes. You can also have a look at the cohesion graph to spot any un-connected, or weakly-connected components.
Once you have determined the fields that belong together, you can apply the Extract Class refactoring. If the component makes sense as a sub-class, Extract Subclass is also a candidate, and is often faster.
While breaking up the class, it is a good idea to analyze how other classes use LoadBalancer, and based on these observations, apply Extract Interface, too.
| 1 | <?php |
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| 30 | class LoadBalancer { |
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| 31 | /** @var array[] Map of (server index => server config array) */ |
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| 32 | private $mServers; |
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| 33 | /** @var array[] Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */ |
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| 34 | private $mConns; |
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| 35 | /** @var array Map of (server index => weight) */ |
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| 36 | private $mLoads; |
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| 37 | /** @var array[] Map of (group => server index => weight) */ |
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| 38 | private $mGroupLoads; |
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| 39 | /** @var bool Whether to disregard slave lag as a factor in slave selection */ |
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| 40 | private $mAllowLagged; |
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| 41 | /** @var integer Seconds to spend waiting on slave lag to resolve */ |
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| 42 | private $mWaitTimeout; |
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| 43 | /** @var array LBFactory information */ |
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| 44 | private $mParentInfo; |
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| 45 | |||
| 46 | /** @var string The LoadMonitor subclass name */ |
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| 47 | private $mLoadMonitorClass; |
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| 48 | /** @var LoadMonitor */ |
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| 49 | private $mLoadMonitor; |
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| 50 | /** @var BagOStuff */ |
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| 51 | private $srvCache; |
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| 52 | |||
| 53 | /** @var bool|DatabaseBase Database connection that caused a problem */ |
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| 54 | private $mErrorConnection; |
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| 55 | /** @var integer The generic (not query grouped) slave index (of $mServers) */ |
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| 56 | private $mReadIndex; |
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| 57 | /** @var bool|DBMasterPos False if not set */ |
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| 58 | private $mWaitForPos; |
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| 59 | /** @var bool Whether the generic reader fell back to a lagged slave */ |
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| 60 | private $laggedSlaveMode = false; |
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| 61 | /** @var bool Whether the generic reader fell back to a lagged slave */ |
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| 62 | private $slavesDownMode = false; |
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| 63 | /** @var string The last DB selection or connection error */ |
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| 64 | private $mLastError = 'Unknown error'; |
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| 65 | /** @var string|bool Reason the LB is read-only or false if not */ |
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| 66 | private $readOnlyReason = false; |
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| 67 | /** @var integer Total connections opened */ |
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| 68 | private $connsOpened = 0; |
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| 69 | |||
| 70 | /** @var TransactionProfiler */ |
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| 71 | protected $trxProfiler; |
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| 72 | |||
| 73 | /** @var integer Warn when this many connection are held */ |
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| 74 | const CONN_HELD_WARN_THRESHOLD = 10; |
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| 75 | /** @var integer Default 'max lag' when unspecified */ |
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| 76 | const MAX_LAG = 10; |
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| 77 | /** @var integer Max time to wait for a slave to catch up (e.g. ChronologyProtector) */ |
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| 78 | const POS_WAIT_TIMEOUT = 10; |
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| 79 | |||
| 80 | /** |
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| 81 | * @var boolean |
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| 82 | */ |
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| 83 | private $disabled = false; |
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| 84 | |||
| 85 | /** |
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| 86 | * @param array $params Array with keys: |
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| 87 | * - servers : Required. Array of server info structures. |
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| 88 | * - loadMonitor : Name of a class used to fetch server lag and load. |
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| 89 | * - readOnlyReason : Reason the master DB is read-only if so [optional] |
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| 90 | * @throws MWException |
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| 91 | */ |
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| 92 | public function __construct( array $params ) { |
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| 145 | |||
| 146 | /** |
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| 147 | * Get a LoadMonitor instance |
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| 148 | * |
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| 149 | * @return LoadMonitor |
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| 150 | */ |
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| 151 | private function getLoadMonitor() { |
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| 159 | |||
| 160 | /** |
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| 161 | * Get or set arbitrary data used by the parent object, usually an LBFactory |
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| 162 | * @param mixed $x |
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| 163 | * @return mixed |
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| 164 | */ |
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| 165 | public function parentInfo( $x = null ) { |
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| 168 | |||
| 169 | /** |
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| 170 | * @param array $loads |
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| 171 | * @param bool|string $wiki Wiki to get non-lagged for |
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| 172 | * @param int $maxLag Restrict the maximum allowed lag to this many seconds |
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| 173 | * @return bool|int|string |
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| 174 | */ |
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| 175 | private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = self::MAX_LAG ) { |
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| 217 | |||
| 218 | /** |
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| 219 | * Get the index of the reader connection, which may be a slave |
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| 220 | * This takes into account load ratios and lag times. It should |
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| 221 | * always return a consistent index during a given invocation |
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| 222 | * |
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| 223 | * Side effect: opens connections to databases |
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| 224 | * @param string|bool $group Query group, or false for the generic reader |
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| 225 | * @param string|bool $wiki Wiki ID, or false for the current wiki |
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| 226 | * @throws MWException |
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| 227 | * @return bool|int|string |
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| 228 | */ |
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| 229 | public function getReaderIndex( $group = false, $wiki = false ) { |
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| 357 | |||
| 358 | /** |
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| 359 | * Set the master wait position |
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| 360 | * If a DB_SLAVE connection has been opened already, waits |
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| 361 | * Otherwise sets a variable telling it to wait if such a connection is opened |
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| 362 | * @param DBMasterPos $pos |
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| 363 | */ |
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| 364 | public function waitFor( $pos ) { |
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| 375 | |||
| 376 | /** |
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| 377 | * Set the master wait position and wait for a "generic" slave to catch up to it |
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| 378 | * |
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| 379 | * This can be used a faster proxy for waitForAll() |
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| 380 | * |
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| 381 | * @param DBMasterPos $pos |
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| 382 | * @param int $timeout Max seconds to wait; default is mWaitTimeout |
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| 383 | * @return bool Success (able to connect and no timeouts reached) |
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| 384 | * @since 1.26 |
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| 385 | */ |
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| 386 | public function waitForOne( $pos, $timeout = null ) { |
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| 406 | |||
| 407 | /** |
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| 408 | * Set the master wait position and wait for ALL slaves to catch up to it |
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| 409 | * @param DBMasterPos $pos |
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| 410 | * @param int $timeout Max seconds to wait; default is mWaitTimeout |
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| 411 | * @return bool Success (able to connect and no timeouts reached) |
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| 412 | */ |
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| 413 | public function waitForAll( $pos, $timeout = null ) { |
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| 426 | |||
| 427 | /** |
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| 428 | * Get any open connection to a given server index, local or foreign |
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| 429 | * Returns false if there is no connection open |
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| 430 | * |
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| 431 | * @param int $i |
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| 432 | * @return DatabaseBase|bool False on failure |
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| 433 | */ |
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| 434 | public function getAnyOpenConnection( $i ) { |
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| 443 | |||
| 444 | /** |
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| 445 | * Wait for a given slave to catch up to the master pos stored in $this |
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| 446 | * @param int $index Server index |
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| 447 | * @param bool $open Check the server even if a new connection has to be made |
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| 448 | * @param int $timeout Max seconds to wait; default is mWaitTimeout |
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| 449 | * @return bool |
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| 450 | */ |
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| 451 | protected function doWait( $index, $open = false, $timeout = null ) { |
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| 508 | |||
| 509 | /** |
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| 510 | * Get a connection by index |
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| 511 | * This is the main entry point for this class. |
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| 512 | * |
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| 513 | * @param int $i Server index |
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| 514 | * @param array|string|bool $groups Query group(s), or false for the generic reader |
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| 515 | * @param string|bool $wiki Wiki ID, or false for the current wiki |
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| 516 | * |
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| 517 | * @throws MWException |
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| 518 | * @return DatabaseBase |
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| 519 | */ |
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| 520 | public function getConnection( $i, $groups = [], $wiki = false ) { |
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| 586 | |||
| 587 | /** |
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| 588 | * Mark a foreign connection as being available for reuse under a different |
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| 589 | * DB name or prefix. This mechanism is reference-counted, and must be called |
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| 590 | * the same number of times as getConnection() to work. |
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| 591 | * |
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| 592 | * @param DatabaseBase $conn |
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| 593 | * @throws MWException |
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| 594 | */ |
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| 595 | public function reuseConnection( $conn ) { |
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| 633 | |||
| 634 | /** |
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| 635 | * Get a database connection handle reference |
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| 636 | * |
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| 637 | * The handle's methods wrap simply wrap those of a DatabaseBase handle |
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| 638 | * |
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| 639 | * @see LoadBalancer::getConnection() for parameter information |
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| 640 | * |
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| 641 | * @param int $db |
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| 642 | * @param array|string|bool $groups Query group(s), or false for the generic reader |
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| 643 | * @param string|bool $wiki Wiki ID, or false for the current wiki |
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| 644 | * @return DBConnRef |
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| 645 | */ |
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| 646 | public function getConnectionRef( $db, $groups = [], $wiki = false ) { |
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| 649 | |||
| 650 | /** |
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| 651 | * Get a database connection handle reference without connecting yet |
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| 652 | * |
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| 653 | * The handle's methods wrap simply wrap those of a DatabaseBase handle |
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| 654 | * |
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| 655 | * @see LoadBalancer::getConnection() for parameter information |
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| 656 | * |
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| 657 | * @param int $db |
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| 658 | * @param array|string|bool $groups Query group(s), or false for the generic reader |
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| 659 | * @param string|bool $wiki Wiki ID, or false for the current wiki |
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| 660 | * @return DBConnRef |
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| 661 | */ |
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| 662 | public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) { |
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| 665 | |||
| 666 | /** |
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| 667 | * Open a connection to the server given by the specified index |
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| 668 | * Index must be an actual index into the array. |
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| 669 | * If the server is already open, returns it. |
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| 670 | * |
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| 671 | * On error, returns false, and the connection which caused the |
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| 672 | * error will be available via $this->mErrorConnection. |
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| 673 | * |
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| 674 | * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError. |
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| 675 | * |
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| 676 | * @param int $i Server index |
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| 677 | * @param string|bool $wiki Wiki ID, or false for the current wiki |
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| 678 | * @return DatabaseBase|bool Returns false on errors |
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| 679 | */ |
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| 680 | public function openConnection( $i, $wiki = false ) { |
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| 711 | |||
| 712 | /** |
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| 713 | * Open a connection to a foreign DB, or return one if it is already open. |
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| 714 | * |
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| 715 | * Increments a reference count on the returned connection which locks the |
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| 716 | * connection to the requested wiki. This reference count can be |
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| 717 | * decremented by calling reuseConnection(). |
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| 718 | * |
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| 719 | * If a connection is open to the appropriate server already, but with the wrong |
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| 720 | * database, it will be switched to the right database and returned, as long as |
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| 721 | * it has been freed first with reuseConnection(). |
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| 722 | * |
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| 723 | * On error, returns false, and the connection which caused the |
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| 724 | * error will be available via $this->mErrorConnection. |
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| 725 | * |
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| 726 | * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError. |
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| 727 | * |
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| 728 | * @param int $i Server index |
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| 729 | * @param string $wiki Wiki ID to open |
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| 730 | * @return DatabaseBase |
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| 731 | */ |
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| 732 | private function openForeignConnection( $i, $wiki ) { |
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| 788 | |||
| 789 | /** |
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| 790 | * Test if the specified index represents an open connection |
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| 791 | * |
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| 792 | * @param int $index Server index |
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| 793 | * @access private |
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| 794 | * @return bool |
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| 795 | */ |
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| 796 | private function isOpen( $index ) { |
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| 803 | |||
| 804 | /** |
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| 805 | * Really opens a connection. Uncached. |
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| 806 | * Returns a Database object whether or not the connection was successful. |
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| 807 | * @access private |
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| 808 | * |
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| 809 | * @param array $server |
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| 810 | * @param bool $dbNameOverride |
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| 811 | * @throws MWException |
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| 812 | * @return DatabaseBase |
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| 813 | */ |
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| 814 | protected function reallyOpenConnection( $server, $dbNameOverride = false ) { |
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| 856 | |||
| 857 | /** |
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| 858 | * @throws DBConnectionError |
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| 859 | * @return bool |
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| 860 | */ |
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| 861 | private function reportConnectionError() { |
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| 890 | |||
| 891 | /** |
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| 892 | * @return int |
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| 893 | * @since 1.26 |
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| 894 | */ |
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| 895 | public function getWriterIndex() { |
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| 898 | |||
| 899 | /** |
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| 900 | * Returns true if the specified index is a valid server index |
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| 901 | * |
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| 902 | * @param string $i |
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| 903 | * @return bool |
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| 904 | */ |
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| 905 | public function haveIndex( $i ) { |
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| 908 | |||
| 909 | /** |
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| 910 | * Returns true if the specified index is valid and has non-zero load |
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| 911 | * |
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| 912 | * @param string $i |
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| 913 | * @return bool |
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| 914 | */ |
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| 915 | public function isNonZeroLoad( $i ) { |
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| 918 | |||
| 919 | /** |
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| 920 | * Get the number of defined servers (not the number of open connections) |
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| 921 | * |
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| 922 | * @return int |
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| 923 | */ |
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| 924 | public function getServerCount() { |
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| 927 | |||
| 928 | /** |
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| 929 | * Get the host name or IP address of the server with the specified index |
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| 930 | * Prefer a readable name if available. |
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| 931 | * @param string $i |
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| 932 | * @return string |
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| 933 | */ |
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| 934 | public function getServerName( $i ) { |
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| 945 | |||
| 946 | /** |
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| 947 | * Return the server info structure for a given index, or false if the index is invalid. |
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| 948 | * @param int $i |
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| 949 | * @return array|bool |
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| 950 | */ |
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| 951 | public function getServerInfo( $i ) { |
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| 958 | |||
| 959 | /** |
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| 960 | * Sets the server info structure for the given index. Entry at index $i |
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| 961 | * is created if it doesn't exist |
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| 962 | * @param int $i |
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| 963 | * @param array $serverInfo |
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| 964 | */ |
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| 965 | public function setServerInfo( $i, array $serverInfo ) { |
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| 968 | |||
| 969 | /** |
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| 970 | * Get the current master position for chronology control purposes |
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| 971 | * @return mixed |
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| 972 | */ |
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| 973 | public function getMasterPos() { |
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| 991 | |||
| 992 | /** |
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| 993 | * Disable this load balancer. All connections are closed, and any attempt to |
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| 994 | * open a new connection will result in a DBAccessError. |
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| 995 | * |
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| 996 | * @since 1.27 |
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| 997 | */ |
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| 998 | public function disable() { |
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| 1002 | |||
| 1003 | /** |
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| 1004 | * Close all open connections |
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| 1005 | */ |
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| 1006 | public function closeAll() { |
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| 1022 | |||
| 1023 | /** |
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| 1024 | * Close a connection |
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| 1025 | * Using this function makes sure the LoadBalancer knows the connection is closed. |
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| 1026 | * If you use $conn->close() directly, the load balancer won't update its state. |
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| 1027 | * @param DatabaseBase $conn |
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| 1028 | */ |
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| 1029 | public function closeConnection( $conn ) { |
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| 1048 | |||
| 1049 | /** |
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| 1050 | * Commit transactions on all open connections |
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| 1051 | * @param string $fname Caller name |
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| 1052 | */ |
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| 1053 | public function commitAll( $fname = __METHOD__ ) { |
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| 1065 | |||
| 1066 | /** |
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| 1067 | * Issue COMMIT only on master, only if queries were done on connection |
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| 1068 | * @param string $fname Caller name |
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| 1069 | */ |
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| 1070 | public function commitMasterChanges( $fname = __METHOD__ ) { |
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| 1084 | |||
| 1085 | /** |
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| 1086 | * Issue ROLLBACK only on master, only if queries were done on connection |
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| 1087 | * @param string $fname Caller name |
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| 1088 | * @throws DBExpectedError |
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| 1089 | * @since 1.23 |
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| 1090 | */ |
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| 1091 | public function rollbackMasterChanges( $fname = __METHOD__ ) { |
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| 1117 | |||
| 1118 | /** |
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| 1119 | * @return bool Whether a master connection is already open |
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| 1120 | * @since 1.24 |
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| 1121 | */ |
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| 1122 | public function hasMasterConnection() { |
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| 1125 | |||
| 1126 | /** |
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| 1127 | * Determine if there are pending changes in a transaction by this thread |
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| 1128 | * @since 1.23 |
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| 1129 | * @return bool |
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| 1130 | */ |
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| 1131 | public function hasMasterChanges() { |
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| 1146 | |||
| 1147 | /** |
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| 1148 | * Get the timestamp of the latest write query done by this thread |
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| 1149 | * @since 1.25 |
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| 1150 | * @return float|bool UNIX timestamp or false |
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| 1151 | */ |
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| 1152 | View Code Duplication | public function lastMasterChangeTimestamp() { |
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| 1166 | |||
| 1167 | /** |
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| 1168 | * Check if this load balancer object had any recent or still |
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| 1169 | * pending writes issued against it by this PHP thread |
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| 1170 | * |
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| 1171 | * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout] |
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| 1172 | * @return bool |
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| 1173 | * @since 1.25 |
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| 1174 | */ |
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| 1175 | public function hasOrMadeRecentMasterChanges( $age = null ) { |
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| 1181 | |||
| 1182 | /** |
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| 1183 | * Get the list of callers that have pending master changes |
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| 1184 | * |
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| 1185 | * @return array |
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| 1186 | * @since 1.27 |
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| 1187 | */ |
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| 1188 | View Code Duplication | public function pendingMasterChangeCallers() { |
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| 1204 | |||
| 1205 | /** |
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| 1206 | * @param mixed $value |
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| 1207 | * @return mixed |
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| 1208 | */ |
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| 1209 | public function waitTimeout( $value = null ) { |
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| 1212 | |||
| 1213 | /** |
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| 1214 | * @note This method will trigger a DB connection if not yet done |
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| 1215 | * |
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| 1216 | * @param string|bool $wiki Wiki ID, or false for the current wiki |
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| 1217 | * @return bool Whether the generic connection for reads is highly "lagged" |
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| 1218 | */ |
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| 1219 | public function getLaggedSlaveMode( $wiki = false ) { |
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| 1235 | |||
| 1236 | /** |
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| 1237 | * @note This method will never cause a new DB connection |
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| 1238 | * @return bool Whether any generic connection used for reads was highly "lagged" |
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| 1239 | * @since 1.27 |
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| 1240 | */ |
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| 1241 | public function laggedSlaveUsed() { |
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| 1244 | |||
| 1245 | /** |
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| 1246 | * @note This method may trigger a DB connection if not yet done |
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| 1247 | * @param string|bool $wiki Wiki ID, or false for the current wiki |
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| 1248 | * @return string|bool Reason the master is read-only or false if it is not |
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| 1249 | * @since 1.27 |
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| 1250 | */ |
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| 1251 | public function getReadOnlyReason( $wiki = false ) { |
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| 1266 | |||
| 1267 | /** |
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| 1268 | * Disables/enables lag checks |
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| 1269 | * @param null|bool $mode |
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| 1270 | * @return bool |
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| 1271 | */ |
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| 1272 | public function allowLagged( $mode = null ) { |
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| 1280 | |||
| 1281 | /** |
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| 1282 | * @return bool |
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| 1283 | */ |
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| 1284 | public function pingAll() { |
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| 1299 | |||
| 1300 | /** |
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| 1301 | * Call a function with each open connection object |
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| 1302 | * @param callable $callback |
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| 1303 | * @param array $params |
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| 1304 | */ |
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| 1305 | public function forEachOpenConnection( $callback, array $params = [] ) { |
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| 1315 | |||
| 1316 | /** |
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| 1317 | * Get the hostname and lag time of the most-lagged slave |
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| 1318 | * |
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| 1319 | * This is useful for maintenance scripts that need to throttle their updates. |
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| 1320 | * May attempt to open connections to slaves on the default DB. If there is |
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| 1321 | * no lag, the maximum lag will be reported as -1. |
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| 1322 | * |
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| 1323 | * @param bool|string $wiki Wiki ID, or false for the default database |
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| 1324 | * @return array ( host, max lag, index of max lagged host ) |
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| 1325 | */ |
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| 1326 | public function getMaxLag( $wiki = false ) { |
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| 1346 | |||
| 1347 | /** |
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| 1348 | * Get an estimate of replication lag (in seconds) for each server |
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| 1349 | * |
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| 1350 | * Results are cached for a short time in memcached/process cache |
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| 1351 | * |
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| 1352 | * Values may be "false" if replication is too broken to estimate |
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| 1353 | * |
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| 1354 | * @param string|bool $wiki |
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| 1355 | * @return int[] Map of (server index => float|int|bool) |
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| 1356 | */ |
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| 1357 | public function getLagTimes( $wiki = false ) { |
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| 1365 | |||
| 1366 | /** |
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| 1367 | * Get the lag in seconds for a given connection, or zero if this load |
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| 1368 | * balancer does not have replication enabled. |
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| 1369 | * |
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| 1370 | * This should be used in preference to Database::getLag() in cases where |
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| 1371 | * replication may not be in use, since there is no way to determine if |
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| 1372 | * replication is in use at the connection level without running |
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| 1373 | * potentially restricted queries such as SHOW SLAVE STATUS. Using this |
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| 1374 | * function instead of Database::getLag() avoids a fatal error in this |
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| 1375 | * case on many installations. |
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| 1376 | * |
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| 1377 | * @param IDatabase $conn |
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| 1378 | * @return int|bool Returns false on error |
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| 1379 | */ |
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| 1380 | public function safeGetLag( IDatabase $conn ) { |
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| 1387 | |||
| 1388 | /** |
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| 1389 | * Wait for a slave DB to reach a specified master position |
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| 1390 | * |
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| 1391 | * This will connect to the master to get an accurate position if $pos is not given |
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| 1392 | * |
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| 1393 | * @param IDatabase $conn Slave DB |
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| 1394 | * @param DBMasterPos|bool $pos Master position; default: current position |
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| 1395 | * @param integer $timeout Timeout in seconds |
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| 1396 | * @return bool Success |
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| 1397 | * @since 1.27 |
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| 1398 | */ |
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| 1399 | public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) { |
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| 1422 | |||
| 1423 | /** |
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| 1424 | * Clear the cache for slag lag delay times |
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| 1425 | * |
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| 1426 | * This is only used for testing |
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| 1427 | */ |
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| 1428 | public function clearLagTimeCache() { |
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| 1431 | } |
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| 1432 |
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In PHP it is possible to write to properties without declaring them. For example, the following is perfectly valid PHP code:
Generally, it is a good practice to explictly declare properties to avoid accidental typos and provide IDE auto-completion: