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ndb - Update documentation wrt scans

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ndb/include/ndbapi/Ndb.hpp:
  Update documentation wrt scans
ndb/include/ndbapi/NdbIndexScanOperation.hpp:
  Update documentation wrt scans
ndb/include/ndbapi/NdbOperation.hpp:
  Update documentation wrt scans
ndb/include/ndbapi/NdbRecAttr.hpp:
  Update documentation wrt scans
ndb/include/ndbapi/NdbScanOperation.hpp:
  Update documentation wrt scans
ndb/include/ndbapi/NdbTransaction.hpp:
  Update documentation wrt scans
ndb/src/ndbapi/NdbOperationSearch.cpp:
  Update documentation wrt scans
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unknown 2004-12-28 11:59:33 +01:00
parent 29b3edb9b4
commit badf354985
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ndb/include/ndbapi/Ndb.hpp
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@ -52,15 +52,6 @@
The execution can be of two different types,
<var>Commit</var> or <var>NoCommit</var>.
*/
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
/**
(A transaction's execution can also be divided into three
steps: prepare, send, and poll. This allows us to perform asynchronous
transactions. More about this later.)
*/
#endif
/**
If the execution is of type <var>NoCommit</var>,
then the application program executes part of a transaction,
but without committing the transaction.
@ -94,28 +85,13 @@
To execute several parallel synchronous transactions, one can either
use multiple <code>Ndb</code> objects in several threads, or start multiple
applications programs.
*/
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
/**
Another way to execute several parallel transactions is to use
asynchronous transactions.
*/
#endif
/**
@section secNdbOperations Operations
Each <code>NdbTransaction</code> (that is, a transaction)
Each <code>NdbTransaction</code>
consists of a list of operations which are represented by instances
of <code>Ndb*Operation</code>.
*/
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
/**
Operations are of two different kinds:
-# standard operations, and
-# interpreted program operations.
*/
#endif
/**
<h3>Single row operations</h3>
After the operation is created using <code>NdbTransaction::getNdbOperation()</code>
(or <code>NdbTransaction::getNdbIndexOperation()</code>), it is defined in the following
@ -163,11 +139,8 @@
We will now discuss in somewhat greater detail each step involved in the creation
and use of synchronous transactions.
*/
// Edit stop point - JS, 20041228 0425+1000
/**
<h4>Step 1: Define single row operation type</h4>
The following types of operations exist:
-# NdbOperation::insertTuple :
@ -207,14 +180,13 @@
Normally the attribute is defined by its name but it is
also possible to use the attribute identity to define the
attribute.
The mapping from name to identity is performed by the Table object.
NdbIndexOperation::getValue returns an NdbRecAttr object
NdbOperation::getValue returns an NdbRecAttr object
containing the read value.
To get the value, there is actually two methods.
The application can either
- use its own memory (passed through a pointer aValue) to
NdbIndexOperation::getValue, or
NdbOperation::getValue, or
- receive the attribute value in an NdbRecAttr object allocated
by the NDB API.
@ -224,7 +196,466 @@
Ndb::closeTransaction have been called.
The result of reading data from an NdbRecAttr object before
calling NdbTransaction::execute is undefined.
@subsection secScan Scan Operations
Scans are roughly the equivalent of SQL cursors.
Scans can either be performed on a table (@ref NdbScanOperation) or
on an ordered index (@ref NdbIndexScanOperation).
Scan operation are characteriesed by the following:
- They can only perform reads (shared, exclusive or dirty)
- They can potentially work with multiple rows
- They can be used to update or delete multiple rows
- They can operate on several nodes in parallell
After the operation is created using <code>NdbTransaction::getNdbScanOperation()</code>
(or <code>NdbTransaction::getNdbIndexScanOperation()</code>), it is defined in the following
three steps:
-# Define the standard operation type, using <code>NdbScanOperation::readTuples()</code>
-# Specify search conditions, using @ref NdbScanFilter and/or @ref NdbIndexScanOperation::setBound
-# Specify attribute actions, using <code>NdbOperation::getValue()</code>
-# Executing the transaction, using <code>NdbTransaction::execute()</code>
-# Iterating through the result set using <code>NdbScanOperation::nextResult</code>
Here are two brief examples illustrating this process. For the sake of brevity,
we omit error-handling.
This first example uses an <code>NdbScanOperation</code>:
@code
// 1. Create
MyOperation= MyTransaction->getNdbScanOperation("MYTABLENAME");
// 2. Define type of operation and lock mode
MyOperation->readTuples(NdbOperation::LM_Read);
// 3. Specify Search Conditions
NdbScanFilter sf(MyOperation);
sf.begin(NdbScanFilter::OR);
sf.eq(0, i); // Return rows with column 0 equal to i or
sf.eq(1, i+1); // column 1 equal to (i+1)
sf.end();
// 4. Attribute Actions
MyRecAttr= MyOperation->getValue("ATTR2", NULL);
@endcode
The second example uses an <code>NdbIndexScanOperation</code>:
@code
// 1. Create
MyOperation= MyTransaction->getNdbIndexScanOperation("MYORDEREDINDEX", "MYTABLENAME");
// 2. Define type of operation and lock mode
MyOperation->readTuples(NdbOperation::LM_Read);
// 3. Specify Search Conditions
// All rows with ATTR1 between i and (i+1)
MyOperation->setBound("ATTR1", NdbIndexScanOperation::BoundGE, i);
MyOperation->setBound("ATTR1", NdbIndexScanOperation::BoundLE, i+1);
// 4. Attribute Actions
MyRecAttr = MyOperation->getValue("ATTR2", NULL);
@endcode
<h4>Step 1: Define scan operation operation type</h4>
Scan operations only support 1 operation, @ref NdbScanOperation::readTuples or @ref NdbIndexScanOperation::readTuples
@note If you want to define multiple scan operations within the same transaction,
then you need to call NdbTransaction::getNdb*ScanOperation for each
operation.
<h4>Step 2: Specify Search Conditions</h4>
The search condition is used to select tuples.
If no search condition is specified, the scan will return all rows
in the table.
Search condition can be @ref NdbScanFilter which can be used on both
@ref NdbScanOperation and @ref NdbIndexScanOperation or bounds which
can only be used on index scans, @ref NdbIndexScanOperation::setBound.
An index scan can have both NdbScanFilter and bounds
@note When NdbScanFilter is used each row is examined but maybe not
returned. But when using bounds, only rows within bounds will be examined.
<h4>Step 3: Specify Attribute Actions</h4>
Now it is time to define which attributes should be read.
Normally the attribute is defined by its name but it is
also possible to use the attribute identity to define the
attribute.
NdbOperation::getValue returns an NdbRecAttr object
containing the read value.
To get the value, there is actually two methods.
The application can either
- use its own memory (passed through a pointer aValue) to
NdbOperation::getValue, or
- receive the attribute value in an NdbRecAttr object allocated
by the NDB API.
The NdbRecAttr object is released when Ndb::closeTransaction
is called.
Thus, the application can not reference this object after
Ndb::closeTransaction have been called.
The result of reading data from an NdbRecAttr object before
calling NdbTransaction::execute is undefined.
<h3> Using Scan to update/delete </h3>
Scanning can also be used to update/delete rows.
This is performed by
-# Scan using exclusive locks, NdbOperation::LM_Exclusive
-# When iterating through the result set, for each row optionally call
either NdbScanOperation::updateCurrentTuple or
NdbScanOperation::deleteCurrentTuple
-# If performing <code>NdbScanOperation::updateCurrentTuple</code>,
set new values on record using ordinary @ref NdbOperation::setValue.
NdbOperation::equal should _not_ be called as the primary key is
retreived from the scan.
@note that the actual update/delete will not be performed until next
NdbTransaction::execute (as with single row operations),
NdbTransaction::execute needs to be called before locks are released,
see @ref secScanLocks
<h4> Index scans specific features </h4>
The following features are available when performing an index scan
- Scan subset of table using @ref NdbIndexScanOperation::setBound
- Ordering result set ascending or descending, @ref NdbIndexScanOperation::readTuples
- When using NdbIndexScanOperation::BoundEQ on distribution key
only fragment containing rows will be scanned.
Rows are returned unordered unless sorted is set to true.
@note When performing sorted scan, parameter parallelism to readTuples will
be ignored and max parallelism will be used instead.
@subsection secScanLocks Lock handling with scans
When scanning a table or an index potentially
a lot of records will be returned.
But Ndb will only lock a batch of rows per fragment at a time.
How many rows will be locked per fragment is controlled by the
<code>batch</code> parameter to @ref NdbScanOperation::readTuples.
To let the application handle how locks are released
@ref NdbScanOperation::nextResult have a parameter <code>fetch_allow</code>.
If NdbScanOperation::nextResult is called with fetch_allow = false, no
locks may be released as result of the function call. Otherwise the locks
for the current batch may be released.
This example shows scan delete, handling locks in an efficient manner.
For the sake of brevity, we omit error-handling.
@code
int check;
// Outer loop for each batch of rows
while((check = MyScanOperation->nextResult(true)) == 0)
{
do
{
// Inner loop for each row within batch
MyScanOperation->deleteCurrentTuple();
} while((check = MyScanOperation->nextResult(false) == 0));
// When no more rows in batch, exeute all defined deletes
MyTransaction->execute(NoCommit);
}
@endcode
See @ref ndbapi_scan.cpp for full example of scan.
@section secError Error Handling
Errors can occur when
-# operations are being defined, or when the
-# transaction is being executed.
One recommended way to handle a transaction failure
(i.e. an error is reported) is to:
-# Rollback transaction (NdbTransaction::execute with a special parameter)
-# Close transaction
-# Restart transaction (if the error was temporary)
@note Transaction are not automatically closed when an error occur.
Several errors can occur when a transaction holds multiple
operations which are simultaneously executed.
In this case the application has to go through the operation
objects and query for their NdbError objects to find out what really
happened.
NdbTransaction::getNdbErrorOperation returns a reference to the
operation causing the latest error.
NdbTransaction::getNdbErrorLine delivers the method number of the
erroneous method in the operation.
@code
theTransaction = theNdb->startTransaction();
theOperation = theTransaction->getNdbOperation("TEST_TABLE");
if (theOperation == NULL) goto error;
theOperation->readTuple(NdbOperation::LM_Read);
theOperation->setValue("ATTR_1", at1);
theOperation->setValue("ATTR_2", at1); //Here an error occurs
theOperation->setValue("ATTR_3", at1);
theOperation->setValue("ATTR_4", at1);
if (theTransaction->execute(Commit) == -1) {
errorLine = theTransaction->getNdbErrorLine();
errorOperation = theTransaction->getNdbErrorOperation();
@endcode
Here errorLine will be 3 as the error occurred in the third method
on the operation object.
Getting errorLine == 0 means that the error occurred when executing the
operations.
Here errorOperation will be a pointer to the theOperation object.
NdbTransaction::getNdbError will return the NdbError object
including holding information about the error.
Since errors could have occurred even when a commit was reported,
there is also a special method, NdbTransaction::commitStatus,
to check the commit status of the transaction.
*******************************************************************************/
/**
* @page ndbapi_example1.cpp ndbapi_example1.cpp
* @include ndbapi_example1.cpp
*/
/**
* @page ndbapi_example2.cpp ndbapi_example2.cpp
* @include ndbapi_example2.cpp
*/
/**
* @page ndbapi_example3.cpp ndbapi_example3.cpp
* @include ndbapi_example3.cpp
*/
/**
* @page ndbapi_example4.cpp ndbapi_example4.cpp
* @include ndbapi_example4.cpp
*/
/**
* @page ndbapi_scan.cpp ndbapi_scan.cpp
* @include ndbapi_scan.cpp
*/
/**
@page secAdapt Adaptive Send Algorithm
At the time of "sending" the transaction
(using NdbTransaction::execute), the transactions
are in reality <em>not</em> immediately transfered to the NDB Kernel.
Instead, the "sent" transactions are only kept in a
special send list (buffer) in the Ndb object to which they belong.
The adaptive send algorithm decides when transactions should
be transfered to the NDB kernel.
For each of these "sent" transactions, there are three
possible states:
-# Waiting to be transferred to NDB Kernel.
-# Has been transferred to the NDB Kernel and is currently
being processed.
-# Has been transferred to the NDB Kernel and has
finished processing.
Now it is waiting for a call to a poll method.
(When the poll method is invoked,
then the transaction callback method will be executed.)
The poll method invoked (either Ndb::pollNdb or Ndb::sendPollNdb)
will return when:
-# at least 'minNoOfEventsToWakeup' of the transactions
in the send list have transitioned to state 3 as described above, and
-# all of these transactions have executed their callback methods.
Since the NDB API is designed as a multi-threaded interface,
it is desirable to transfer database operations from more than
one thread at a time.
The NDB API keeps track of which Ndb objects are active in transfering
information to the NDB kernel and the expected amount of threads to
interact with the NDB kernel.
Note that an Ndb object should be used in at most one thread.
Two different threads should <em>not</em> use the same Ndb object.
There are four reasons leading to transfering of database
operations:
-# The NDB Transporter (TCP/IP, OSE, SCI or shared memory)
decides that a buffer is full and sends it off.
The buffer size is implementation dependent and
might change between NDB Cluster releases.
On TCP/IP the buffer size is usually around 64 kByte and
on OSE/Delta it is usually less than 2000 bytes.
In each Ndb object there is one buffer per DB node,
so this criteria of a full buffer is only
local to the connection to one DB node.
-# Statistical information on the transfered information
may force sending of buffers to all DB nodes.
-# Every 10 ms a special send-thread checks whether
any send activity has occurred. If not, then the thread will
force sending to all nodes.
This means that 20 ms is the maximum time database operations
are waiting before being sent off. The 10 millisecond limit
is likely to become a configuration parameter in
later releases of NDB Cluster.
However, to support faster than 10 ms checks,
there has to be support from the operating system.
-# When calling NdbTransaction::execute synchronously or calling any
of the poll-methods, there is a force parameter that overrides the
adaptive algorithm and forces the send to all nodes.
@note The times mentioned above are examples. These might
change in later releases of NDB Cluster.
*/
/**
@page secConcepts NDB Cluster Concepts
The <em>NDB Kernel</em> is the collection of database (DB) nodes
belonging to an NDB Cluster.
The application programmer can for most purposes view the
set of all DB nodes as one entity.
Each DB node has three main components:
- TC : The transaction coordinator
- ACC : The index storage
- TUP : The data storage
When the application program executes a transaction,
it connects to one TC on one DB node.
Usually, the programmer does not need to specify which TC to use,
but some cases when performance is important,
transactions can be hinted to use a certain TC.
(If the node with the TC is down, then another TC will
automatically take over the work.)
Every DB node has an ACC and a TUP which stores
the index and the data part of the database.
Even though one TC is responsible for the transaction,
several ACCs and TUPs on other DB nodes might be involved in the
execution of the transaction.
@section secNdbKernelConnection Selecting Transaction Coordinator
The default method is to select the transaction coordinator (TC) as being
the "closest" DB node. There is a heuristics for closeness based on
the type of transporter connection. In order of closest first, we have
SCI, SHM, TCP/IP (localhost), and TCP/IP (remote host). If there are several
connections available with the same "closeness", they will each be
selected in a round robin fashion for every transaction. Optionally
one may set the methos for TC selection round robin over all available
connections, where each new set of transactions
is placed on the next DB node.
The application programmer can however hint the NDB API which
transaction coordinator to use
by providing a <em>distribution key</em> (usually the primary key).
By using the primary key as distribution key,
the transaction will be placed on the node where the primary replica
of that record resides.
Note that this is only a hint, the system can be
reconfigured and then the NDB API will choose a transaction
coordinator without using the hint.
For more information, see NdbDictionary::Column::setDistributionKey.
@section secRecordStruct Record Structure
NDB Cluster is a relational database with tables of records.
Table rows represent tuples of relational data stored as records.
When created, the attribute schema of the table is specified,
and thus each record of the table has the same schema.
@subsection secKeys Primary Keys
Each record has from 1 up to 32 attributes which belong
to the primary key of the table.
@section secTrans Transactions
Transactions are committed to main memory,
and are committed to disk after a global checkpoint, GCP.
Since all data is (in most NDB Cluster configurations)
synchronously replicated and stored on multiple NDB nodes,
the system can still handle processor failures without loss
of data.
However, in the case of a system failure (e.g. the whole system goes down),
then all (committed or not) transactions after the latest GCP are lost.
@subsection secConcur Concurrency Control
NDB Cluster uses pessimistic concurrency control based on locking.
If a requested lock (implicit and depending on database operation)
cannot be attained within a specified time,
then a timeout error occurs.
Concurrent transactions (parallel application programs, thread-based
applications)
sometimes deadlock when they try to access the same information.
Applications need to be programmed so that timeout errors
occurring due to deadlocks are handled. This generally
means that the transaction encountering timeout
should be rolled back and restarted.
@section secHint Hints and performance
Placing the transaction coordinator close
to the actual data used in the transaction can in many cases
improve performance significantly. This is particularly true for
systems using TCP/IP. A system using Solaris and a 500 MHz processor
has a cost model for TCP/IP communication which is:
30 microseconds + (100 nanoseconds * no of Bytes)
This means that if we can ensure that we use "popular" links we increase
buffering and thus drastically reduce the communication cost.
Systems using SCI has a different cost model which is:
5 microseconds + (10 nanoseconds * no of Bytes)
Thus SCI systems are much less dependent on selection of
transaction coordinators.
Typically TCP/IP systems spend 30-60% of the time during communication,
whereas SCI systems typically spend 5-10% of the time during
communication.
Thus SCI means that less care from the NDB API programmer is
needed and great scalability can be achieved even for applications using
data from many parts of the database.
A simple example is an application that uses many simple updates where
a transaction needs to update one record.
This record has a 32 bit primary key,
which is also the distribution key.
Then the keyData will be the address of the integer
of the primary key and keyLen will be 4.
*/
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
/**
(A transaction's execution can also be divided into three
steps: prepare, send, and poll. This allows us to perform asynchronous
transactions. More about this later.)
*/
#endif
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
/**
Another way to execute several parallel transactions is to use
asynchronous transactions.
*/
#endif
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
/**
Operations are of two different kinds:
-# standard operations, and
-# interpreted program operations.
*/
#endif
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
/**
<h3>Interpreted Program Operations</h3>
@ -233,10 +664,6 @@
updates a tuple using an interpreted program
-# NdbOperation::interpretedDeleteTuple :
delete a tuple using an interpreted program
-# NdbOperation::openScanRead :
scans a table with read lock on each tuple
-# NdbOperation::openScanExclusive :
scans a table with exclusive update lock on each tuple
The operations interpretedUpdateTuple and interpretedDeleteTuple both
work using the unique tuple key.
@ -289,122 +716,6 @@
NdbOperation::def_subroutine and NdbOperation::ret_sub.
*/
#endif
/**
@subsection secScan Scanning
The most common use of interpreted programs is for scanning
tables. Scanning is a search of all tuples in a table.
Tuples which satisfy conditions (a search filter)
stated in the interpreted program
are sent to the application.
Reasons for using scan transactions include
need to use a search key different from the primary key
and any secondary index.
Or that the query needs to access so many tuples so that
it is more efficient to scan the entire table.
Scanning can also be used to update information.
The scanning transaction itself is however
not allowed to update any tuples.
To do updates via scanning transactions, the tuples
need to be handed over to another transaction which is
executing the actual update.
Even though a scan operation is part of a transaction,
the scan transaction is not a normal transaction.
The locks are <em>not</em> kept throughout the entire
scan transaction, since this would imply non-optimal performance.
<em>
A transaction containing a scan operation can only
contain that operation.
No other operations are allowed in the same transaction.
</em>
The NdbOperation::openScanRead operation
only sets a temporary read lock while
reading the tuple.
The tuple lock is released already when the
result of the read reaches the application.
The NdbOperation::openScanExclusive operation sets an
exclusive lock on the tuple
and sends the result to the application.
Thus when the application reads the data it is still
locked with the exclusive lock.
If the application desires to update the tuple it may transfer
the tuple to another transaction which updates the tuple.
The updating transaction can consist of a combination of tuples
received from the scan and normal operations.
For transferred operations it is not necessary to provide the
primary key. It is part of the transfer.
You only need to give the operation type and the
actions to perform on the tuple.
The scan transaction starts like a usual transaction,
but is of the following form:
-# Start transaction
-# Get NdbOperation for the table to be scanned
-# Set the operation type using NdbOperation::openScanRead or
NdbOperation::openScanExclusive
-# Search conditions are defined by an interpreted program
(setValue and write_attr are not allowed, since scan transactions
are only allowed to read information).
The instruction interpret_exit_nok does in this case
not abort the transaction, it only skips the tuple and
proceeds with the next.
The skipped tuple will not be reported to the application.
-# Call NdbTransaction::executeScan to define (and start) the scan.
-# Call NdbTransaction::nextScanResult to proceed with next tuple.
When calling NdbTransaction::nextScanResult, the lock on any
previous tuples are released.
<br>
If the tuple should be updated then it must be transferred over
to another updating transaction.
This is performed by calling
NdbOperation::takeOverForUpdate or takeOverForDelete on
the scanning transactions NdbOperation object with the updating
transactions NdbTransaction object as parameter.
<p>
If NdbOperation::takeOverFor* returns NULL then the
operation was not successful, otherwise it returns a reference
to the NdbOperation which the updating transaction has received
-# Use Ndb::closeTransaction as usual to close the transaction.
This can be performed even if there are more tuples to scan.
See also example program in section @ref select_all.cpp.
However, a new scan api is under development, using NdbScanOperation
and NdbScanFilter. NdbScanFilter makes it easier to define a search
criteria and is recommended instead of using Interpreted Programs.
The scan transaction starts like a usual transaction,
but is of the following form:
-# Start transaction
-# Get NdbScanOperation for the table to be scanned
-# NdbScanOperation::readTuples(NdbOperation::LM_Exclusive) returns a handle to a
NdbResultSet.
-# Search conditions are defined by NdbScanFilter
-# Call NdbTransaction::execute(NoCommit) to start the scan.
-# Call NdbResultSet::nextResult to proceed with next tuple.
When calling NdbResultSet::nextResult(false), the lock on any
previous tuples are released and the next tuple cached in the API
is fetched.
<br>
If the tuple should be updated then define a new update operation
(NdbOperation) using NdbResultSet::updateTuple().
The new update operation can the be used to modify the tuple.
When nextResult(false) returns != 0, then no more tuples
are cached in the API. Updated tuples is now commit using
NdbTransaction::execute(Commit).
After the commit, more tuples are fetched from NDB using
nextResult(true).
-# Use Ndb::closeTransaction as usual to close the transaction.
This can be performed even if there are more tuples to scan.
See the scan example program in @ref ndbapi_scan.cppn for example
usage of the new scan api.
*/
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
/**
<h3>Interpreted Programs</h3>
@ -584,234 +895,11 @@
*/
#endif
/**
@section secError Error Handling
Errors can occur when
-# operations are being defined, or when the
-# transaction is being executed.
One recommended way to handle a transaction failure
(i.e. an error is reported) is to:
-# Rollback transaction (NdbTransaction::execute with a special parameter)
-# Close transaction
-# Restart transaction (if the error was temporary)
@note Transaction are not automatically closed when an error occur.
Several errors can occur when a transaction holds multiple
operations which are simultaneously executed.
In this case the application has to go through the operation
objects and query for their NdbError objects to find out what really
happened.
NdbTransaction::getNdbErrorOperation returns a reference to the
operation causing the latest error.
NdbTransaction::getNdbErrorLine delivers the method number of the
erroneous method in the operation.
@code
theTransaction = theNdb->startTransaction();
theOperation = theTransaction->getNdbOperation("TEST_TABLE");
if (theOperation == NULL) goto error;
theOperation->readTuple(NdbOperation::LM_Read);
theOperation->setValue("ATTR_1", at1);
theOperation->setValue("ATTR_2", at1); //Here an error occurs
theOperation->setValue("ATTR_3", at1);
theOperation->setValue("ATTR_4", at1);
if (theTransaction->execute(Commit) == -1) {
errorLine = theTransaction->getNdbErrorLine();
errorOperation = theTransaction->getNdbErrorOperation();
@endcode
Here errorLine will be 3 as the error occurred in the third method
on the operation object.
Getting errorLine == 0 means that the error occurred when executing the
operations.
Here errorOperation will be a pointer to the theOperation object.
NdbTransaction::getNdbError will return the NdbError object
including holding information about the error.
Since errors could have occurred even when a commit was reported,
there is also a special method, NdbTransaction::commitStatus,
to check the commit status of the transaction.
*******************************************************************************/
/**
* @page ndbapi_example1.cpp ndbapi_example1.cpp
* @include ndbapi_example1.cpp
*/
/**
* @page ndbapi_example2.cpp ndbapi_example2.cpp
* @include ndbapi_example2.cpp
*/
/**
* @page ndbapi_example3.cpp ndbapi_example3.cpp
* @include ndbapi_example3.cpp
*/
/**
* @page ndbapi_example4.cpp ndbapi_example4.cpp
* @include ndbapi_example4.cpp
*/
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
/**
* @page select_all.cpp select_all.cpp
* @include select_all.cpp
*/
/**
* @page ndbapi_async.cpp ndbapi_async.cpp
* @include ndbapi_async.cpp
*/
#endif
/**
* @page ndbapi_scan.cpp ndbapi_scan.cpp
* @include ndbapi_scan.cpp
*/
/**
@page secAdapt Adaptive Send Algorithm
At the time of "sending" the transaction
(using NdbTransaction::execute), the transactions
are in reality <em>not</em> immediately transfered to the NDB Kernel.
Instead, the "sent" transactions are only kept in a
special send list (buffer) in the Ndb object to which they belong.
The adaptive send algorithm decides when transactions should
be transfered to the NDB kernel.
For each of these "sent" transactions, there are three
possible states:
-# Waiting to be transferred to NDB Kernel.
-# Has been transferred to the NDB Kernel and is currently
being processed.
-# Has been transferred to the NDB Kernel and has
finished processing.
Now it is waiting for a call to a poll method.
(When the poll method is invoked,
then the transaction callback method will be executed.)
The poll method invoked (either Ndb::pollNdb or Ndb::sendPollNdb)
will return when:
-# at least 'minNoOfEventsToWakeup' of the transactions
in the send list have transitioned to state 3 as described above, and
-# all of these transactions have executed their callback methods.
Since the NDB API is designed as a multi-threaded interface,
it is desirable to transfer database operations from more than
one thread at a time.
The NDB API keeps track of which Ndb objects are active in transfering
information to the NDB kernel and the expected amount of threads to
interact with the NDB kernel.
Note that an Ndb object should be used in at most one thread.
Two different threads should <em>not</em> use the same Ndb object.
There are four reasons leading to transfering of database
operations:
-# The NDB Transporter (TCP/IP, OSE, SCI or shared memory)
decides that a buffer is full and sends it off.
The buffer size is implementation dependent and
might change between NDB Cluster releases.
On TCP/IP the buffer size is usually around 64 kByte and
on OSE/Delta it is usually less than 2000 bytes.
In each Ndb object there is one buffer per DB node,
so this criteria of a full buffer is only
local to the connection to one DB node.
-# Statistical information on the transfered information
may force sending of buffers to all DB nodes.
-# Every 10 ms a special send-thread checks whether
any send activity has occurred. If not, then the thread will
force sending to all nodes.
This means that 20 ms is the maximum time database operations
are waiting before being sent off. The 10 millisecond limit
is likely to become a configuration parameter in
later releases of NDB Cluster.
However, to support faster than 10 ms checks,
there has to be support from the operating system.
-# When calling NdbTransaction::execute synchronously or calling any
of the poll-methods, there is a force parameter that overrides the
adaptive algorithm and forces the send to all nodes.
@note The times mentioned above are examples. These might
change in later releases of NDB Cluster.
*/
/**
@page secConcepts NDB Cluster Concepts
The <em>NDB Kernel</em> is the collection of database (DB) nodes
belonging to an NDB Cluster.
The application programmer can for most purposes view the
set of all DB nodes as one entity.
Each DB node has three main components:
- TC : The transaction coordinator
- ACC : The index storage
- TUP : The data storage
When the application program executes a transaction,
it connects to one TC on one DB node.
Usually, the programmer does not need to specify which TC to use,
but some cases when performance is important,
transactions can be hinted to use a certain TC.
(If the node with the TC is down, then another TC will
automatically take over the work.)
Every DB node has an ACC and a TUP which stores
the index and the data part of the database.
Even though one TC is responsible for the transaction,
several ACCs and TUPs on other DB nodes might be involved in the
execution of the transaction.
@section secNdbKernelConnection Selecting Transaction Coordinator
The default method is to select the transaction coordinator (TC) as being
the "closest" DB node. There is a heuristics for closeness based on
the type of transporter connection. In order of closest first, we have
SCI, SHM, TCP/IP (localhost), and TCP/IP (remote host). If there are several
connections available with the same "closeness", they will each be
selected in a round robin fashion for every transaction. Optionally
one may set the methos for TC selection round robin over all available
connections, where each new set of transactions
is placed on the next DB node.
The application programmer can however hint the NDB API which
transaction coordinator to use
by providing a <em>distribution key</em> (usually the primary key).
By using the primary key as distribution key,
the transaction will be placed on the node where the primary replica
of that record resides.
Note that this is only a hint, the system can be
reconfigured and then the NDB API will choose a transaction
coordinator without using the hint.
For more information, see NdbDictionary::Column::setDistributionKey.
@section secRecordStruct Record Structure
NDB Cluster is a relational database with tables of records.
Table rows represent tuples of relational data stored as records.
When created, the attribute schema of the table is specified,
and thus each record of the table has the same schema.
@subsection secKeys Tuple Keys
Each record has from zero up to four attributes which belong
to the primary key of the table.
If no attribute belongs to the primary key, then
the NDB Cluster creates an attribute named <em>NDB$TID</em>
which stores a tuple identity.
The <em>tuple key</em> of a table is thus either
the primary key attributes or the special NDB$TID attribute.
Put this back when real array ops are supported
i.e. get/setValue("kalle[3]");
@subsection secArrays Array Attributes
A table attribute in NDB Cluster can be of <em>array type</em>.
@ -819,66 +907,7 @@
<em>elements</em>. The <em>attribute size</em> is the size
of one element of the array (expressed in bits) and the
<em>array size</em> is the number of elements of the array.
@section secTrans Transactions
Transactions are committed to main memory,
and are committed to disk after a global checkpoint, GCP.
Since all data is (in most NDB Cluster configurations)
synchronously replicated and stored on multiple NDB nodes,
the system can still handle processor failures without loss
of data.
However, in the case of a system failure (e.g. the whole system goes down),
then all (committed or not) transactions after the latest GCP are lost.
@subsection secConcur Concurrency Control
NDB Cluster uses pessimistic concurrency control based on locking.
If a requested lock (implicit and depending on database operation)
cannot be attained within a specified time,
then a timeout error occurs.
Concurrent transactions (parallel application programs, thread-based
applications)
sometimes deadlock when they try to access the same information.
Applications need to be programmed so that timeout errors
occurring due to deadlocks are handled. This generally
means that the transaction encountering timeout
should be rolled back and restarted.
@section secHint Hints and performance
Placing the transaction coordinator close
to the actual data used in the transaction can in many cases
improve performance significantly. This is particularly true for
systems using TCP/IP. A system using Solaris and a 500 MHz processor
has a cost model for TCP/IP communication which is:
30 microseconds + (100 nanoseconds * no of Bytes)
This means that if we can ensure that we use "popular" links we increase
buffering and thus drastically reduce the communication cost.
Systems using SCI has a different cost model which is:
5 microseconds + (10 nanoseconds * no of Bytes)
Thus SCI systems are much less dependent on selection of
transaction coordinators.
Typically TCP/IP systems spend 30-60% of the time during communication,
whereas SCI systems typically spend 5-10% of the time during
communication.
Thus SCI means that less care from the NDB API programmer is
needed and great scalability can be achieved even for applications using
data from many parts of the database.
A simple example is an application that uses many simple updates where
a transaction needs to update one record.
This record has a 32 bit primary key,
which is also the distribution key.
Then the keyData will be the address of the integer
of the primary key and keyLen will be 4.
*/
#ifndef Ndb_H

30
ndb/include/ndbapi/NdbIndexScanOperation.hpp
View file

@ -34,16 +34,15 @@ class NdbIndexScanOperation : public NdbScanOperation {
public:
/**
* readTuples returns a NdbResultSet where tuples are stored.
* Tuples are not stored in NdbResultSet until execute(NoCommit)
* has been executed and nextResult has been called.
* readTuples using ordered index
*
* @param parallel Scan parallelism
* @param lock_mode Lock mode
* @param batch No of rows to fetch from each fragment at a time
* @param LockMode Scan lock handling
* @param parallel No of fragments to scan in parallel
* @param order_by Order result set in index order
* @param order_desc Order descending, ignored unless order_by
* @returns NdbResultSet.
* @param order_desc Order descending, ignored unless order_by
* @param read_range_no Enable reading of range no using @ref get_range_no
* @returns 0 for success and -1 for failure
* @see NdbScanOperation::readTuples
*/
int readTuples(LockMode = LM_Read,
@ -53,16 +52,6 @@ public:
bool order_desc = false,
bool read_range_no = false);
#ifndef DOXYGEN_SHOULD_SKIP_DEPRECATED
inline int readTuples(int parallell){
return readTuples(LM_Read, 0, parallell, false);
}
inline int readTuplesExclusive(int parallell = 0){
return readTuples(LM_Exclusive, 0, parallell, false);
}
#endif
/**
* Type of ordered index key bound. The values (0-4) will not change
* and can be used explicitly (e.g. they could be computed).
@ -134,7 +123,14 @@ public:
*/
int get_range_no();
/**
* Is current scan sorted
*/
bool getSorted() const { return m_ordered; }
/**
* Is current scan sorted descending
*/
bool getDescending() const { return m_descending; }
private:
NdbIndexScanOperation(Ndb* aNdb);

25
ndb/include/ndbapi/NdbOperation.hpp
View file

@ -265,21 +265,6 @@ public:
int equal(Uint32 anAttrId, Int64 aValue);
int equal(Uint32 anAttrId, Uint64 aValue);
/**
* Generate a tuple id and set it as search argument.
*
* The Tuple id has NDB$TID as attribute name and 0 as attribute id.
*
* The generated tuple id is returned by the method.
* If zero is returned there is an error.
*
* This is mostly used for tables without any primary key
* attributes.
*
* @return Generated tuple id if successful, otherwise 0.
*/
Uint64 setTupleId();
/** @} *********************************************************************/
/**
* @name Specify Attribute Actions for Operations
@ -708,6 +693,7 @@ public:
/** @} *********************************************************************/
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
/**
* Type of operation
*/
@ -723,11 +709,16 @@ public:
NotDefined2, ///< Internal for debugging
NotDefined ///< Internal for debugging
};
#endif
/**
* Return lock mode for operation
*/
LockMode getLockMode() const { return theLockMode; }
void setAbortOption(Int8 ao) { m_abortOption = ao; }
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
void setAbortOption(Int8 ao) { m_abortOption = ao; }
/**
* Set/get distribution/partition key
*/
@ -758,8 +749,10 @@ protected:
void next(NdbOperation*); // Set next pointer
NdbOperation* next(); // Get next pointer
public:
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
const NdbOperation* next() const;
const NdbRecAttr* getFirstRecAttr() const;
#endif
protected:
enum OperationStatus

2
ndb/include/ndbapi/NdbRecAttr.hpp
View file

@ -245,7 +245,9 @@ public:
~NdbRecAttr();
public:
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
const NdbRecAttr* next() const;
#endif
private:
NdbRecAttr();

54
ndb/include/ndbapi/NdbScanOperation.hpp
View file

@ -37,16 +37,14 @@ class NdbScanOperation : public NdbOperation {
public:
/**
* readTuples returns a NdbResultSet where tuples are stored.
* Tuples are not stored in NdbResultSet until execute(NoCommit)
* has been executed and nextResult has been called.
* readTuples
*
* @param parallel Scan parallelism
* @param lock_mode Lock mode
* @param batch No of rows to fetch from each fragment at a time
* @param LockMode Scan lock handling
* @param parallel No of fragments to scan in parallell
* @note specifying 0 for batch and parallall means max performance
*/
int readTuples(LockMode = LM_Read,
int readTuples(LockMode lock_mode = LM_Read,
Uint32 batch = 0, Uint32 parallel = 0);
#ifndef DOXYGEN_SHOULD_SKIP_DEPRECATED
@ -67,7 +65,7 @@ public:
/**
* Get the next tuple in a scan transaction.
*
* After each call to NdbResult::nextResult
* After each call to nextResult
* the buffers and NdbRecAttr objects defined in
* NdbOperation::getValue are updated with values
* from the scanned tuple.
@ -114,53 +112,31 @@ public:
int nextResult(bool fetchAllowed = true, bool forceSend = false);
/**
* Close result set (scan)
* Close scan
*/
void close(bool forceSend = false);
/**
* Restart
*/
int restart(bool forceSend = false);
/**
* Transfer scan operation to an updating transaction. Use this function
* when a scan has found a record that you want to update.
* 1. Start a new transaction.
* 2. Call the function takeOverForUpdate using your new transaction
* as parameter, all the properties of the found record will be copied
* to the new transaction.
* 3. When you execute the new transaction, the lock held by the scan will
* be transferred to the new transaction(it's taken over).
* Update current tuple
*
* @note You must have started the scan with openScanExclusive
* to be able to update the found tuple.
*
* @param updateTrans the update transaction connection.
* @return an NdbOperation or NULL.
*/
NdbOperation* updateCurrentTuple();
NdbOperation* updateCurrentTuple(NdbTransaction* updateTrans);
/**
* Transfer scan operation to a deleting transaction. Use this function
* when a scan has found a record that you want to delete.
* 1. Start a new transaction.
* 2. Call the function takeOverForDelete using your new transaction
* as parameter, all the properties of the found record will be copied
* to the new transaction.
* 3. When you execute the new transaction, the lock held by the scan will
* be transferred to the new transaction(its taken over).
*
* @note You must have started the scan with openScanExclusive
* to be able to delete the found tuple.
*
* @param deleteTrans the delete transaction connection.
* @return an NdbOperation or NULL.
* Delete current tuple
* @return 0 on success or -1 on failure
*/
int deleteCurrentTuple();
int deleteCurrentTuple(NdbTransaction* takeOverTransaction);
/**
* Restart scan with exactly the same
* getValues and search conditions
*/
int restart(bool forceSend = false);
protected:
NdbScanOperation(Ndb* aNdb);
virtual ~NdbScanOperation();

22
ndb/include/ndbapi/NdbTransaction.hpp
View file

@ -110,23 +110,6 @@ enum ExecType {
* -# AbortOption::IgnoreError
* Continue execution of transaction even if operation fails
*
* NdbTransaction::execute can sometimes indicate an error
* (return with -1) while the error code on the NdbTransaction is 0.
* This is an indication that one of the operations found a record
* problem. The transaction is still ok and can continue as usual.
* The NdbTransaction::execute returns -1 together with error code
* on NdbTransaction object equal to 0 always means that an
* operation was not successful but that the total transaction was OK.
* By checking error codes on the individual operations it is possible
* to find out which operation was not successful.
*
* NdbTransaction::executeScan is used to setup a scan in the NDB kernel
* after it has been defined.
* NdbTransaction::nextScanResult is used to iterate through the
* scanned tuples.
* After each call to NdbTransaction::nextScanResult, the pointers
* of NdbRecAttr objects defined in the NdbOperation::getValue
* operations are updated with the values of the new the scanned tuple.
*/
/* FUTURE IMPLEMENTATION:
@ -376,6 +359,7 @@ public:
#endif
void close();
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
/**
* Restart transaction
*
@ -385,6 +369,7 @@ public:
* Note this method also releases completed operations
*/
int restart();
#endif
/** @} *********************************************************************/
@ -494,7 +479,7 @@ public:
*/
const NdbOperation * getNextCompletedOperation(const NdbOperation * op)const;
#ifndef DOXYGEN_SHOULD_SKIP_INTERNAL
const NdbOperation* getFirstDefinedOperation()const{return theFirstOpInList;}
const NdbOperation* getLastDefinedOperation()const{return theLastOpInList;}
@ -508,6 +493,7 @@ public:
* ops are used (read, insert, update, delete).
*/
int executePendingBlobOps(Uint8 flags = 0xFF);
#endif
private:
/**

26
ndb/src/ndbapi/NdbOperationSearch.cpp
View file

@ -300,32 +300,6 @@ NdbOperation::equal_impl(const NdbColumnImpl* tAttrInfo,
return -1;
}
/******************************************************************************
* Uint64 setTupleId( void )
*
* Return Value: Return > 0: OK
* Return 0 : setTupleId failed
* Parameters:
* Remark:
*****************************************************************************/
Uint64
NdbOperation::setTupleId()
{
if (theStatus != OperationDefined)
{
return 0;
}
Uint64 tTupleId = theNdb->getTupleIdFromNdb(m_currentTable->m_tableId);
if (tTupleId == ~(Uint64)0){
setErrorCodeAbort(theNdb->theError.code);
return 0;
}
if (equal((Uint32)0, tTupleId) == -1)
return 0;
return tTupleId;
}
/******************************************************************************
* int insertKEYINFO(const char* aValue, aStartPosition,
* anAttrSizeInWords, Uint32 anAttrBitsInLastWord);