private $waitForPos;
/** @var bool Whether the generic reader fell back to a lagged replica DB */
private $laggedReplicaMode = false;
- /** @var bool Whether the generic reader fell back to a lagged replica DB */
- private $allReplicasDownMode = false;
- /** @var string The last DB domain selection or connection error */
+ /** @var string The last DB selection or connection error */
private $lastError = 'Unknown error';
/** @var string|bool Reason this instance is read-only or false if not */
private $readOnlyReason = false;
const MAX_LAG_DEFAULT = 6;
/** @var int Default 'waitTimeout' when unspecified */
const MAX_WAIT_DEFAULT = 10;
- /** @var int Seconds to cache master server read-only status */
+ /** @var int Seconds to cache master DB server read-only status */
const TTL_CACHE_READONLY = 5;
const KEY_LOCAL = 'local';
throw new InvalidArgumentException( "Invalid query groups provided" );
}
- if ( $groups && $i > 0 ) {
+ if ( $groups !== [] && $groups !== false && $i > 0 ) {
$groupList = implode( ', ', $groups );
throw new LogicException( "Got query groups ($groupList) with a server index (#$i)" );
}
}
/**
- * @param int $flags
- * @return bool
+ * @param int $flags Bitfield of class CONN_* constants
+ * @param int $i Specific server index or DB_MASTER/DB_REPLICA
+ * @return int Sanitized bitfield
*/
- private function sanitizeConnectionFlags( $flags ) {
- if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
- // Assuming all servers are of the same type (or similar), which is overwhelmingly
- // the case, use the master 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.
+ private function sanitizeConnectionFlags( $flags, $i ) {
+ // Whether an outside caller is explicitly requesting the master database server
+ if ( $i === self::DB_MASTER || $i === $this->getWriterIndex() ) {
+ $flags |= self::CONN_INTENT_WRITABLE;
+ }
+
+ if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == 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.
+
+ // Master DB server attributes (should match those of the replica DB servers)
$attributes = $this->getServerAttributes( $this->getWriterIndex() );
if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
- // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
- // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
- // to reduce lock contention. None of these apply for sqlite and using separate
- // connections just causes self-deadlocks.
+ // 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;
- $this->connLogger->info( __METHOD__ .
- ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
+ $type = $this->getServerType( $this->getWriterIndex() );
+ $this->connLogger->info( __METHOD__ . ": CONN_TRX_AUTOCOMMIT disallowed ($type)" );
}
}
}
}
- /**
+ /**
* Get a LoadMonitor instance
*
* @return ILoadMonitor
/**
* @param array $loads List of server weights
* @param string|bool $domain
- * @return array (reader index, lagged replica mode) or false on failure
+ * @return array (reader index, lagged replica mode) or (false, false) on failure
*/
private function pickReaderIndex( array $loads, $domain = false ) {
if ( $loads === [] ) {
$serverName = $this->getServerName( $i );
$this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
- $conn = $this->getConnection( $i, [], $domain, self::CONN_SILENCE_ERRORS );
+ // Get a connection to this server without triggering other server connections
+ $flags = self::CONN_SILENCE_ERRORS;
+ $conn = $this->getServerConnection( $i, $domain, $flags );
if ( !$conn ) {
$this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
unset( $currentLoads[$i] ); // avoid this server next iteration
public function getAnyOpenConnection( $i, $flags = 0 ) {
$i = ( $i === self::DB_MASTER ) ? $this->getWriterIndex() : $i;
+ // Connection handles required to be in auto-commit mode use a separate connection
+ // pool since the main pool is effected by implicit and explicit transaction rounds
$autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
$conn = false;
/**
* Wait for a given replica DB to catch up to the master pos stored in "waitForPos"
- * @param int $index Server index
+ * @param int $index Specific server index
* @param bool $open Check the server even if a new connection has to be made
* @param int|null $timeout Max seconds to wait; default is "waitTimeout"
* @return bool
// Find a connection to wait on, creating one if needed and allowed
$close = false; // close the connection afterwards
- $conn = $this->getAnyOpenConnection( $index );
+ $flags = self::CONN_SILENCE_ERRORS;
+ $conn = $this->getAnyOpenConnection( $index, $flags );
if ( !$conn ) {
if ( !$open ) {
$this->replLogger->debug(
return false;
}
- // Open a temporary new connection in order to wait for replication
- $conn = $this->getConnection( $index, [], self::DOMAIN_ANY, self::CONN_SILENCE_ERRORS );
+ // Get a connection to this server without triggering other server connections
+ $conn = $this->getServerConnection( $index, self::DOMAIN_ANY, $flags );
if ( !$conn ) {
$this->replLogger->warning(
__METHOD__ . ': failed to connect to {dbserver}',
}
public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
- $groups = $this->resolveGroups( $groups, $i );
$domain = $this->resolveDomainID( $domain );
- $flags = $this->sanitizeConnectionFlags( $flags );
- $masterOnly = ( $i === self::DB_MASTER || $i === $this->getWriterIndex() );
+ $groups = $this->resolveGroups( $groups, $i );
+ $flags = $this->sanitizeConnectionFlags( $flags, $i );
+ // If given DB_MASTER/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 = $this->getConnectionIndex( $i, $groups, $domain );
+ // Get an open connection to that server (might trigger a new connection)
+ $conn = $this->getServerConnection( $serverIndex, $domain, $flags );
+ // Set master DB handles as read-only if there is high replication lag
+ if ( $serverIndex === $this->getWriterIndex() && $this->getLaggedReplicaMode( $domain ) ) {
+ $reason = ( $this->getExistingReaderIndex( self::GROUP_GENERIC ) >= 0 )
+ ? 'The database is read-only until replication lag decreases.'
+ : 'The database is read-only until replica database servers becomes reachable.';
+ $conn->setLBInfo( 'readOnlyReason', $reason );
+ }
+
+ return $conn;
+ }
+ /**
+ * @param int $i Specific server index
+ * @param string $domain Resolved DB domain
+ * @param int $flags Bitfield of class CONN_* constants
+ * @return IDatabase|bool
+ * @throws InvalidArgumentException When the server index is invalid
+ */
+ public function getServerConnection( $i, $domain, $flags = 0 ) {
// Number of connections made before getting the server index and handle
$priorConnectionsMade = $this->connectionCounter;
- // Choose a server if $i is DB_MASTER/DB_REPLICA (might trigger new connections)
- $serverIndex = $this->getConnectionIndex( $i, $groups, $domain );
- // Get an open connection to that server (might trigger a new connection)
+ // Get an open connection to this server (might trigger a new connection)
$conn = $this->localDomain->equals( $domain )
- ? $this->getLocalConnection( $serverIndex, $flags )
- : $this->getForeignConnection( $serverIndex, $domain, $flags );
- // Throw an error or bail out if the connection attempt failed
+ ? $this->getLocalConnection( $i, $flags )
+ : $this->getForeignConnection( $i, $domain, $flags );
+ // Throw an error or otherwise bail out if the connection attempt failed
if ( !( $conn instanceof IDatabase ) ) {
if ( ( $flags & self::CONN_SILENCE_ERRORS ) != self::CONN_SILENCE_ERRORS ) {
$this->reportConnectionError();
// Profile any new connections caused by this method
if ( $this->connectionCounter > $priorConnectionsMade ) {
- $host = $conn->getServer();
- $dbname = $conn->getDBname();
- $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
+ $this->trxProfiler->recordConnection(
+ $conn->getServer(),
+ $conn->getDBname(),
+ ( ( $flags & self::CONN_INTENT_WRITABLE ) == self::CONN_INTENT_WRITABLE )
+ );
}
if ( !$conn->isOpen() ) {
- // 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.
$this->errorConnection = $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.
return false;
}
+ // Make sure that flags like CONN_TRX_AUTOCOMMIT are respected by this handle
$this->enforceConnectionFlags( $conn, $flags );
- if ( $serverIndex === $this->getWriterIndex() ) {
- // If the load balancer is read-only, perhaps due to replication lag, then master
- // DB handles will reflect that. Note that Database::assertIsWritableMaster() takes
- // care of replica DB handles whereas getReadOnlyReason() would cause infinite loops.
- $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
+ // Set master DB handles as read-only if the load balancer is configured as read-only
+ // or the master database server is running in server-side read-only mode. Note that
+ // replica DB handles are always read-only via Database::assertIsWritableMaster().
+ // Read-only mode due to replication lag is *avoided* here to avoid recursion.
+ if ( $conn->getLBInfo( 'serverIndex' ) === $this->getWriterIndex() ) {
+ if ( $this->readOnlyReason !== false ) {
+ $conn->setLBInfo( 'readOnlyReason', $this->readOnlyReason );
+ } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
+ $conn->setLBInfo(
+ 'readOnlyReason',
+ 'The master database server is running in read-only mode.'
+ );
+ }
}
return $conn;
/**
* @param int $i
- * @param bool $domain
+ * @param string|bool $domain
* @param int $flags
* @return Database|bool Live database handle or false on failure
* @deprecated Since 1.34 Use getConnection() instead
* @param int $i Server index
* @param int $flags Class CONN_* constant bitfield
* @return Database
+ * @throws InvalidArgumentException When the server index is invalid
+ * @throws UnexpectedValueException When the DB domain of the connection is corrupted
*/
private function getLocalConnection( $i, $flags = 0 ) {
// Connection handles required to be in auto-commit mode use a separate connection
* @param int $flags Class CONN_* constant bitfield
* @return Database|bool Returns false on connection 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
*/
private function getForeignConnection( $i, $domain, $flags = 0 ) {
$domainInstance = DatabaseDomain::newFromId( $domain );
}
public function getLaggedReplicaMode( $domain = false ) {
- if (
- // Avoid recursion if there is only one DB
- $this->hasStreamingReplicaServers() &&
- // Avoid recursion if the (non-zero load) master DB was picked for generic reads
- $this->genericReadIndex !== $this->getWriterIndex() &&
- // Stay in lagged replica mode during the load balancer instance lifetime
- !$this->laggedReplicaMode
- ) {
+ if ( $this->laggedReplicaMode ) {
+ return true; // stay in lagged replica mode
+ }
+
+ if ( $this->hasStreamingReplicaServers() ) {
try {
- // Calling this method will set "laggedReplicaMode" as needed
- $this->getReaderIndex( false, $domain );
+ // Set "laggedReplicaMode"
+ $this->getReaderIndex( self::GROUP_GENERIC, $domain );
} catch ( DBConnectionError $e ) {
- // Avoid expensive re-connect attempts and failures
- $this->allReplicasDownMode = true;
+ // Sanity: avoid expensive re-connect attempts and failures
$this->laggedReplicaMode = true;
}
}
public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
if ( $this->readOnlyReason !== false ) {
return $this->readOnlyReason;
- } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
- if ( $this->allReplicasDownMode ) {
- return 'The database has been automatically locked ' .
- 'until the replica database servers become available';
- } else {
- return 'The database has been automatically locked ' .
- 'while the replica database servers catch up to the master.';
- }
} elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
- return 'The database master is running in read-only mode.';
+ return 'The master database server is running in read-only mode.';
+ } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
+ return ( $this->getExistingReaderIndex( self::GROUP_GENERIC ) >= 0 )
+ ? 'The database is read-only until replication lag decreases.'
+ : 'The database is read-only until a replica database server becomes reachable.';
}
return false;
function () use ( $domain, $conn ) {
$old = $this->trxProfiler->setSilenced( true );
try {
- $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
+ $index = $this->getWriterIndex();
+ $dbw = $conn ?: $this->getServerConnection( $index, $domain );
$readOnly = (int)$dbw->serverIsReadOnly();
if ( !$conn ) {
$this->reuseConnection( $dbw );
$readOnly = 0;
}
$this->trxProfiler->setSilenced( $old );
+
return $readOnly;
},
[ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
if ( !$pos ) {
// Get the current master position, opening a connection if needed
$index = $this->getWriterIndex();
- $masterConn = $this->getAnyOpenConnection( $index );
+ $flags = self::CONN_SILENCE_ERRORS;
+ $masterConn = $this->getAnyOpenConnection( $index, $flags );
if ( $masterConn ) {
$pos = $masterConn->getMasterPos();
} else {
- $flags = self::CONN_SILENCE_ERRORS;
- $masterConn = $this->getConnection( $index, [], self::DOMAIN_ANY, $flags );
+ $masterConn = $this->getServerConnection( $index, self::DOMAIN_ANY, $flags );
if ( !$masterConn ) {
throw new DBReplicationWaitError(
null,
dépôts / lhc / web / wiklou.git / commitdiff