2.3.16 The Ndb Class

[+/-]

2.3.16.1 Ndb Class Constructor

2.3.16.2 Ndb::closeTransaction()

2.3.16.3 Ndb::computeHash()

2.3.16.4 Ndb::createEventOperation()

2.3.16.5 Ndb::dropEventOperation()

2.3.16.6 Ndb::getDictionary()

2.3.16.7 Ndb::getDatabaseName()

2.3.16.8 Ndb::getDatabaseSchemaName()

2.3.16.9 Ndb::getGCIEventOperations()

2.3.16.10 Ndb::get_eventbuf_max_alloc()

2.3.16.11 Ndb::get_eventbuffer_free_percent()

2.3.16.12 Ndb::get_event_buffer_memory_usage()

2.3.16.13 Ndb::getHighestQueuedEpoch()

2.3.16.14 Ndb::getLatestGCI()

2.3.16.15 Ndb::getNdbError()

2.3.16.16 Ndb::getNdbErrorDetail()

2.3.16.17 Ndb::getNdbObjectName()

2.3.16.18 Ndb::getNextEventOpInEpoch2()

2.3.16.19 Ndb::getReference()

2.3.16.20 Ndb::init()

2.3.16.21 Ndb::isConsistent()

2.3.16.22 Ndb::isConsistentGCI()

2.3.16.23 Ndb::isExpectingHigherQueuedEpochs()

2.3.16.24 Ndb::nextEvent()

2.3.16.25 Ndb::nextEvent2()

2.3.16.26 Ndb::pollEvents()

2.3.16.27 Ndb::pollEvents2()

2.3.16.28 Ndb::setDatabaseName()

2.3.16.29 Ndb::setDatabaseSchemaName()

2.3.16.30 Ndb::setEventBufferQueueEmptyEpoch()

2.3.16.31 Ndb::set_eventbuf_max_alloc()

2.3.16.32 Ndb::set_eventbuffer_free_percent()

2.3.16.33 Ndb::setNdbObjectName()

2.3.16.34 Ndb::startTransaction()

Abstract

This class represents the NDB kernel; it is the primary class of the NDB API.

Parent class.  None

Child classes.  None

Description.  Any nontrivial NDB API program makes use of at least one instance of Ndb. By using several Ndb objects, it is possible to implement a multi-threaded application. You should remember that one Ndb object cannot be shared between threads; however, it is possible for a single thread to use multiple Ndb objects. A single application process can support a maximum of 4711 Ndb objects.

Resource consumption by Ndb objects.  An Ndb object consumes memory in proportion to the size of the largest operation performed over the lifetime of the object. This is particularly noticeable in cases of large transactions; use of one or both of BLOB or TEXT columns; or both. This memory is held for the lifetime of the object, and once used in this way by the Ndb object, the only way to free this memory is to destroy the object (and then to create a new instance if desired).

Note

The Ndb object is multi-thread safe in that each Ndb object can be handled by one thread at a time. If an Ndb object is handed over to another thread, then the application must ensure that a memory barrier is used to ensure that the new thread sees all updates performed by the previous thread.

Semaphores and mutexes are examples of easy ways to provide memory barriers without having to bother about the memory barrier concept.

It is also possible to use multiple Ndb objects to perform operations on different clusters in a single application. See Application-level partitioning, for conditions and restrictions applying to such usage.

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

Method	Purpose / Use
Ndb()	Class constructor; represents a connection to an NDB Cluster.
~Ndb()	Class destructor; terminates a Cluster connection when it is no longer to be used
closeTransaction()	Closes a transaction.
computeHash()	Computes a distribution hash value.
createEventOperation()	Creates a subscription to a database event. (See Section 2.3.21, “The NdbEventOperation Class”.)
dropEventOperation()	Drops a subscription to a database event.
getDictionary()	Gets a dictionary, which is used for working with database schema information.
getDatabaseName()	Gets the name of the current database.
getDatabaseSchemaName()	Gets the name of the current database schema.
get_eventbuf_max_alloc()	Gets the current allocated maximum size of the event buffer. Added in NDB 7.2.14 and NDB 7.3.3.
get_eventbuffer_free_percent()	Gets the percentage of event buffer memory that should be available before buffering resumes, once the limit has been reached. Added in NDB 7.4.3.
get_event_buffer_memory_usage()	Provides event buffer memory usage information. Added in NDB 7.4.3.
getGCIEventOperations()	Gets the next event operation from a GCI. Deprecated in NDB 7.4.3.
getHighestQueuedEpoch()	Gets the latest epoch in the event queue. Added in NDB 7.4.3.
getLatestGCI()	Gets the most recent GCI. Deprecated in NDB 7.4.3.
getNdbError()	Retrieves an error. (See Section 2.3.20, “The NdbError Structure”.)
getNdbErrorDetail()	Retrieves extra error details.
getNdbObjectName()	Retrieves the Ndb object name if one was set. Added in NDB 7.2.17 and NDB 7.3.6.
getNextEventOpInEpoch2()	Gets the next event operation in this global checkpoint.
getReference()	Retrieves a reference or identifier for the Ndb object instance.
init()	Initializes an Ndb object and makes it ready for use.
isConsistent()	Whether all received events are consistent. Deprecated in NDB 7.4.3.
isConsistentGCI()	Whether all received events for a given global checkpoint are consistent. Deprecated in NDB 7.4.3.
isExpectingHigherQueuedEpochs()	Check whether there are new queued epochs, or there was a cluster failure event. Added in NDB 7.2.21, NDB 7.3.10, and NDB 7.4.7.
nextEvent()	Gets the next event from the queue. Deprecated in NDB 7.4.3.
nextEvent2()	Gets the next event from the queue. Added in NDB 7.4.3.
pollEvents()	Waits for an event to occur. Deprecated in NDB 7.4.3.
pollEvents2()	Waits for an event to occur. Added in NDB 7.4.3.
setDatabaseName()	Sets the name of the current database.
setDatabaseSchemaName()	Sets the name of the current database schema.
setEventBufferQueueEmptyEpoch()	Enables queuing of empty events. Added in NDB 7.4.11 and NDB 7.5.2.
set_eventbuf_max_alloc()	Sets the current allocated maximum size of the event buffer. Added in NDB 7.2.14 and NDB 7.3.3.
set_eventbuffer_free_percent()	Sets the percentage of event buffer memory that should be available before buffering resumes, once the limit has been reached. Added in NDB 7.4.3.
setNdbObjectName()	For debugging purposes: sets an arbitrary name for this Ndb object. Added in NDB 7.2.17 and NDB 7.3.6.
startTransaction()	Begins a transaction. (See Section 2.3.30, “The NdbTransaction Class”.)

Class diagram.  This diagram shows all the available members of the Ndb class:

Figure 2.11 Ndb