Description. This method is used to begin a new transaction. There are three variants, the simplest of these using a table and a partition key or partition ID to specify the transaction coordinator (TC). The third variant makes it possible for you to specify the TC by means of a pointer to the data of the key.
When the transaction is completed it must be closed using
Failure to do so aborts the transaction. This must be done
regardless of the transaction's final outcome, even if it
fails due to an error.
NdbTransaction* startTransaction ( const NdbDictionary::Table* table = 0, const char* keyData = 0, Uint32* keyLen = 0 )
Parameters. This method takes the following three parameters:
table: A pointer to a
Tableobject. This is used to determine on which node the transaction coordinator should run.
keyData: A pointer to a partition key corresponding to
keyLen: The length of the partition key, expressed in bytes.
NdbTransaction* startTransaction ( const NdbDictionary::Table* table, const struct Key_part_ptr* keyData, void* xfrmbuf = 0, Uint32 xfrmbuflen = 0 )
Parameters. When specifying the transaction coordinator, this method takes the four parameters listed here:
A pointer to a
Tableobject) used for deciding which node should act as the transaction coordinator.
A null-terminated array of pointers to the values of the distribution key columns. The length of the key part is read from metadata and checked against the passed value.
A pointer to a temporary buffer, used to calculate the hash value.
The length of the buffer.
(the default), then a call to
free() is made automatically, as appropriate.
startTransaction() fails if
xfrmbuf is not
xfrmbuflen is too small.
Suppose that the table's partition key is a single
BIGINT column. Then you would declare the
distribution key array as shown here:
The value of the distribution key would be defined as shown here:
unsigned long long distkeyValue= 23;
The pointer to the distribution key array would be set as follows:
distkey.ptr= (const void*) &distkeyValue;
The length of this pointer would be set accordingly:
The distribution key array must terminate with a
NULL element. This is necessary to avoid to
having an additional parameter providing the number of columns in
the distribution key:
distkey.ptr= NULL; distkey.len= NULL;
Setting the buffer to
startTransaction() to allocate and free memory
xfrmbuf= NULL; xfrmbuflen= 0;
You can also specify a buffer to save having to make explicit
but calculating an appropriate size for this buffer is not a
simple matter; if the buffer is not
its length is too short, then the startTransaction() call fails.
However, if you choose to specify the buffer, 1 MB is usually a
Now, when you start the transaction, you can access the node that contains the desired information directly.
Another distribution-aware version of this method makes it possible for you to specify a table and partition (using the partition ID) as a hint for selecting the transaction coordinator, and is defined as shown here:
NdbTransaction* startTransaction ( const NdbDictionary::Table* table, Uint32 partitionId )
In the event that the cluster has the same number of data nodes as
it has replicas, specifying the transaction coordinator gains no
improvement in performance, since each data node contains the
entire database. However, where the number of data nodes is
greater than the number of replicas (for example, where
NoOfReplicas is set equal
to 2 in a cluster with 4 data nodes), you should see a marked
improvement in performance by using the distribution-aware version
of this method.
It is still possible to use this method as before, without
specifying the transaction coordinator. In either case, you must
still explicitly close the transaction, whether or not the call to
startTransaction() was successful.
On success, an
object. In the event of failure,