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An NDB application program should begin with the creation of a singleNdb_cluster_connectionobject, and typically makes use of a singleNdb_cluster_connection. The application connects to a cluster management server when this object'sconnect()method is called. By using thewait_until_ready()method it is possible to wait for the connection to reach one or more data nodes.

An instance ofNdb_cluster_connectionis used to create anNdbobject. Prior to NDB 7.3.8 and NDB 7.4.3, it was possible to delete theNdb_cluster_connectionused to create a given instance ofNdbwithout first deleting the dependentNdbobject. (Bug #19999242)

The following table lists the public methods of this class and the purpose or use of each method:

This method creates a connection to an NDB Cluster, that is, to a cluster of data nodes. The object returned by this method is required in order to instantiate anNdbobject. Thus, every NDB API application requires the use of anNdb_cluster_connection.

Ndb_cluster_connectionhas two constructors. The first of these is shown here:

Ndb_cluster_connection ( const char*connection_string= 0 )

The second constructor takes a node ID in addition to the connection string argument. Its signature and parameters are shown here:

Ndb_cluster_connection ( const char*connection_string, intforce_api_nodeid)

The first version of the constructor requires a singleconnection_stringparameter, pointing to the location of the management server.

The second version of the constructor takes two arguments, aconnection_stringand the node ID (force_api_nodeid) to be used by this API node. This node ID overrides any node ID value set in theconnection_stringargument.

An instance ofNdb_cluster_connection.

This method connects to a cluster management server.

int connect ( intretries= 30, intdelay= 1, intverbose= 0 )

This method takes three parameters, all of which are optional:

This method returns anint, which can have one of the following 3 values:

This method retrieves the currentAutoReconnectsetting for a givenNdb_cluster_connection. For more detailed information, seeNdb_cluster_connection::set_auto_reconnect().

int get_auto_reconnect ( void )

None.

An integer value0or1, corresponding to the currentAutoReconnectsetting in effect for for this connection.0forces API nodes to use new connections to the cluster, while1enables API nodes to re-use existing connections.

This method can be used to determine whether or not the most recentconnect()attempt made by thisNdb_cluster_connectionsucceeded . If the connection succeeded,get_latest_error()returns0; otherwise, it returns1. If the connection attempt failed, useNdb_cluster_connection::get_latest_error_msg()to obtain an error message giving the reason for the failure.

int get_latest_error ( void ) const

None.

1or0. A return value of1indicates that the latest attempt to connect failed; if the attempt succeeded, a0is returned.

If the most recent connection attempt by thisNdb_cluster_connectionfailed (as determined by callingget_latest_error()), this method provides an error message supplying information about the reason for the failure.

const char* get_latest_error_msg ( void ) const

None.

A string containing an error message describing a failure byNdb_cluster_connection::connect(). If the most recent connection attempt succeeded, an empty string is returned.

Get the minimum time in milliseconds that is permit to lapse before the adaptive send mechanism forces all pending signals to be sent.

Uint32 get_max_adaptive_send_time ( )

None.

Wait time as a number of milliseconds. This should always be a value between 0 and 10, inclusive.

This method is used to iterate over a set ofNdbobjects, retrieving them one at a time.

const Ndb* get_next_ndb_object ( const Ndb*p)

This method takes a single parameter, a pointer to the lastNdbobject to have been retrieved orNULL.

返回下一个Ndbobject, orNULLif no moreNdbobjects are available.

Get the number of receiver threads.

int get_num_recv_threads ( void ) const

None.

The number of receiver threads.

Get the level set for activating the receiver thread bound byset_recv_thread_cpu().

int get_recv_thread_activation_threshold ( void ) const

None.

An integer threshold value. SeeNdb_cluster_connection::set_recv_thread_activation_threshold(), for information about interpreting this value.

Gets the system name from the cluster configuration. This is the value of theNamesystem configuration parameter set in the cluster'sconfig.iniconfiguration file.

const char* get_system_name ( void ) const

None.

The cluster system name. If not set in the cluster configuration file, this is a generated value in the formMC_timestamp(for example,MC_20170426182343), using the time that the management server was started.

Calling this method prevents the creation of new instances of theNdbclass. This method must be called prior to iterating over multipleNdbobjects usingget_next_ndb_object().

void lock_ndb_objects ( void ) const

This method was madeconstin NDB 7.3.15, 7.4.13, and 7.5.4 (Bug #23709232).

For more information, seeNdb_cluster_connection::get_next_ndb_object().

None.

None.

An API node that is disconnected from the cluster is forced to use a new connection object to reconnect, unless this behavior is overridden by settingAutoReconnect = 1in theconfig.inifile or calling this method with 1 as the input value. Calling the method with 0 for the value has the same effect as setting theAutoReconnectconfiguration parameter (also introduced in those NDB Cluster versions) to 0; that is, API nodes are forced to create new connections.

void set_auto_reconnect ( intvalue)

Avalueof 0 or 1 which determines API node reconnection behavior. 0 forces API nodes to use new connections (Ndb_cluster_connectionobjects); 1 permits API nodes to re-use existing connections to the cluster.

None.

Set data node neighbor of the connection, used for optimal placement of the transaction coordinator. This method be used after creating theNdb_cluster_connection, but prior to starting any query threads. This is due to the fact that this method may change the internal state of theNdb_cluster_connection共享的线程使用。这种状态是不thread-safe; changing it can lead to non-optimal node selection at the time of the change.

You can use thendb_data_node_neighbourserver system variable to set a data node neighbor for an NDB Cluster SQL node.

This method was added in NDB 7.5.2.

void set_data_node_neighbour ( Uint32neighbour_node)

The ID of the node to be used as the neighbor.

None.

Set the minimum time in milliseconds that is permit to lapse before the adaptive send mechanism forces all pending signals to be sent.

void set_max_adaptive_send_time ( Uint32milliseconds)

Wait time in milliseconds. The range is 0-10, with 10 being the default value.

None.

Sets a name for the connection. If the name is specified, it is reported in the cluster log.

void set_name ( const char*name)

Thenameto be used as an identifier for the connection.

None.

Set the number of receiver threads bound to the CPU (or CPUs) determined usingset_recv_thread_cpu()and with the threshold set byset_recv_thread_activation_threshold().

This method should be invoked before trying to connect to any other nodes.

int集_num_recv_threads ( Uint32num_recv_threads)

The number of receive threads. The only supported value is1.

-1indicates an error; any other value indicates success.

This method can be used to override theconnect()method's default behavior as regards which node should be connected to first.

void set_optimized_node_selection ( intvalue)

An integervalue.

None.

Set the level for activating the receiver thread bound byset_recv_thread_cpu(). Below this level, normal user threads are used to receive signals.

int集_recv_thread_activation_threshold ( Uint32threshold)

An integerthreshold价值。16或更高意味着接收线程never used as receivers. 0 means that the receive thread is always active, and that retains poll rights for its own exclusive use, effectively blocking all user threads from becoming receivers. In such cases care should be taken to ensure that the receive thread does not compete with the user thread for CPU resources; it is preferable for it to be locked to a CPU for its own exclusive use. The default is 8.

-1indicates an error; any other value indicates success.

Beginning with NDB 7.5.7 and NDB 7.6.2, this method can be used to create a URI for publication inservice_URIcolumn of the the application's row in thendbinfo.processestable.

Provided that this method is called prior to invokingconnect(), the service URI is published immediately upon connection; otherwise, it is published after a delay of up toHeartbeatIntervalDbApimilliseconds.

int集_service_uri ( const char*scheme, const char*host, intport, const char*path)

This method takes the parameters listed here:

0 on success, 1 in the event of a syntax error.

Set the CPU or CPUs to which the receiver thread should be bound. Set the level for activating the receiver thread as a receiver by invokingset_recv_thread_activation_threshold(). Unset the binding for this receiver thread by invokingunset_recv_thread_cpu().

int集_recv_thread_cpu ( Uint16*cpuid_array, Uint32array_len, Uint32recv_thread_id= 0 )

This method takes three parameters, listed here:

-1indicates an error; any other value indicates success.

Used to set a timeout for the connection, to limit the amount of time that we may block when connecting.

This method is actually a wrapper for the MGM API functionndb_mgm_set_timeout().

int集_timeout ( inttimeout_ms)

The length of the timeout, in milliseconds (timeout_ms). Currently, only multiples of 1000 are accepted.

0 on success; any other value indicates failure.

This method undoes the effects of thelock_ndb_objects()method, making it possible to create new instances ofNdb.unlock_ndb_objects()should be called after you have finished retrievingNdbobjects using theget_next_ndb_object()method.

void unlock_ndb_objects ( void ) const

This method was madeconstin NDB 7.3.15, 7.4.13, and 7.5.4 (Bug #23709232).

For more information, seeNdb_cluster_connection::get_next_ndb_object().

None.

None.

Unset the CPU or CPUs to which the receiver thread was bound usingset_recv_thread_cpu().

int unset_recv_thread_cpu ( Uint32recv_thread_id)

The thread ID of the receiver thread to be unbound.

-1indicates an error; any other value indicates success.

This method is needed to establish connections with the data nodes. It waits until the requested connection with one or more data nodes is successful, or until a timeout condition is met.

int wait_until_ready ( inttimeoutBefore, inttimeoutAfter)

This method takes two parameters:

wait_until_ready()returns anint, whose value is interpreted as follows: