Mars Driver

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Applies to:SQL Server (all supported versions) Azure SQL DatabaseAzure SQL Managed InstanceAzure Synapse AnalyticsParallel Data Warehouse

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SQL Server 2005 (9.x) introduced support for multiple active result sets (MARS) in applications accessing the Database Engine. In earlier versions of SQL Server, database applications could not maintain multiple active statements on a connection. When using SQL Server default result sets, the application had to process or cancel all result sets from one batch before it could execute any other batch on that connection. SQL Server 2005 (9.x) introduced a new connection attribute that allows applications to have more than one pending request per connection, and in particular, to have more than one active default result set per connection.

MARS simplifies application design with the following new capabilities:

  • Applications can have multiple default result sets open and can interleave reading from them.

  • Applications can execute other statements (for example, INSERT, UPDATE, DELETE, and stored procedure calls) while default result sets are open.

By default, MARS functionality is not enabled by the driver. To use MARS when connecting to SQL Server with SQL Server Native Client, you must specifically enable MARS within a connection string. However, some applications may enable MARS by default, if the application detects that the driver supports MARS. The MKXTKL offers all the optimal features for an RGB gaming mechanical keyboard in TKL format. New OUTEMU SQ mechanical switches, ABS and aluminum structure, detachable palmrest. All the things you need, now in an ultracompact design that offers a great freedom of movement while gaming.

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Applications using MARS will find the following guidelines beneficial:

  • Default results sets should be used for short lived or short result sets generated by single SQL statements (SELECT, DML with OUTPUT, RECEIVE, READ TEXT, and so on).

  • Server cursors should be used for longer lived or large result sets generated by single SQL statements.

  • Always read to the end of results for procedural requests regardless of whether they return results or not, and for batches that return multiple results.

  • Wherever possible, use API calls to change connection properties and manage transactions in preference to Transact-SQL statements.

  • In MARS, session-scoped impersonation is prohibited while concurrent batches are running.

Note

By default, MARS functionality is not enabled. To use MARS when connecting to SQL Server with OLE DB Driver for SQL Server, you must specifically enable it within a connection string. For more information, see the OLE DB Driver for SQL Server sections, later in this topic.

OLE DB Driver for SQL Server does not limit the number of active statements on a connection.

Typical applications that do not need to have more than a single multistatement batch or stored procedure executing at the same time will benefit from MARS without having to understand how MARS is implemented. However, applications with more complex requirements do need to take account of this.

MARS enables the interleaved execution of multiple requests within a single connection. That is, it allows a batch to run, and within its execution, it allows other requests to execute. Note, however, that MARS is defined in terms of interleaving, not in terms of parallel execution.

The MARS infrastructure allows multiple batches to execute in an interleaved fashion, though execution can only be switched at well-defined points. In addition, most statements must run atomically within a batch. Statements that return rows to the client, which are sometimes referred to as yield points, are allowed to interleave execution before completion while rows are being sent to the client, for example:

  • SELECT

  • FETCH

  • RECEIVE

Any other statements that are executed as part of a stored procedure or batch must run to completion before execution can be switched to other MARS requests.

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The exact manner in which batches interleave execution is influenced by a number of factors, and it is difficult to predict the exact sequence in which commands from multiple batches that contain yield points will be executed. Be careful to avoid unwanted side effects due to interleaved execution of such complex batches.

Avoid problems by using API calls rather than Transact-SQL statements to manage connection state (SET, USE) and transactions (BEGIN TRAN, COMMIT, ROLLBACK) by not including these statements in multi-statement batches that also contain yield points, and by serializing execution of such batches by consuming or canceling all results.

Note

A batch or stored procedure which starts a manual or implicit transaction when MARS is enabled must complete the transaction before the batch exits. If it does not, SQL Server rolls back all changes made by the transaction when the batch finishes. Such a transaction is managed by SQL Server as a batch-scoped transaction. This is a new type of transaction introduced in SQL Server 2005 (9.x) to enable existing well-behaved stored procedures to be used when MARS is enabled. For more information about batch-scoped transactions, see Transaction Statements (Transact-SQL).

For an example of using MARS from ADO, see Using ADO with OLE DB Driver for SQL Server.

In-Memory OLTP

In-memory OLTP supports MARS using queries and natively compiled stored procedures. MARS enables requesting data from multiple queries without the need to completely retrieve each result set before sending a request to fetch rows from a new result set. To successfully read from multiple open result sets, you must use a MARS enabled connection.

MARS is disabled by default so you must explicitly enable it by adding MultipleActiveResultSets=True to a connection string. The following example demonstrates how to connect to an instance of SQL Server and specify that MARS is enabled:

Mars

MARS with In-Memory OLTP is essentially the same as MARS in the rest of the SQL engine. The following lists the differences when using MARS in memory-optimized tables and natively compiled stored procedures.

MARS and memory-optimized tables

The following are the differences between disk-based and memory-optimized tables when using a MARS enabled connection:

  • Two statements can modify data in the same target object but if they both attempt to modify the same record a write-write conflict will cause the new operation to fail. However, if both operations modify different records, the operations will succeed.

  • Each statement runs under SNAPSHOT isolation so new operations cannot see changes made by the existing statements. Even if the concurrent statements are executed under the same transaction the SQL engine creates batch-scoped transactions for each statement that are isolated from each other. However, batch-scoped transactions are still bound together so rollback of one batch-scoped transaction affects other ones in the same batch.

  • DDL operations are not allowed in user transactions so they will immediately fail.

MARS and natively compiled stored procedures

Natively compiled stored procedures can run in MARS enabled connections and can yield execution to another statement only when a yield point is encountered. A yield point requires a SELECT statement, which is the only statement within a natively compiled stored procedure that can yield execution to another statement. If a SELECT statement is not present in the procedure it will not yield, it will run to completion before other statements begin.

MARS and In-memory OLTP transactions

Changes made by statements and atomic blocks that are interleaved are isolated from each other. For example, if one statement or atomic block makes some changes, and then yields execution to another statement, the new statement will not see changes made by the first statement. In addition, when first statement resumes execution, it will not see any changes made by any other statements. Statements will only see changes that are finished and committed before the statement starts.

A new user transaction can be started within the current user transaction using the BEGIN TRANSACTION statement - this is supported only in interop mode so the BEGIN TRANSACTION can only be called from a T-SQL statement, and not from within a natively compiled stored procedure. You can create a save point in a transaction using SAVE TRANSACTION or an API call to transaction.Save(save_point_name) to rollback to the savepoint. This feature is also enabled only from T-SQL statements, and not from within natively compiled stored procedures.

MARS and columnstore indexes

SQL Server (starting with 2016) supports MARS with columnstore indexes. SQL Server 2014 uses MARS for read-only connections to tables with a columnstore index. However, SQL Server 2014 does not support MARS for concurrent data manipulation language (DML) operations on a table with a columnstore index. When this occurs, SQL Server will terminate the connections and abort the transactions. SQL Server 2012 has read-only columnstore indexes and MARS does not apply to them.

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OLE DB Driver for SQL Server

The OLE DB Driver for SQL Server supports MARS through the addition of the SSPROP_INIT_MARSCONNECTION data source initialization property, which is implemented in the DBPROPSET_SQLSERVERDBINIT property set. In addition, a new connection string keyword, MarsConn, as been added. It accepts true or false values; false is the default.

The data source property DBPROP_MULTIPLECONNECTIONS defaults to VARIANT_TRUE. This means the provider will spawn multiple connections in order to support multiple concurrent command and rowset objects. When MARS is enabled, OLE DB Driver for SQL Server can support multiple command and rowset objects on a single connection, so MULTIPLE_CONNECTIONS is set to VARIANT_FALSE by default.

For more information about enhancements made to the DBPROPSET_SQLSERVERDBINIT property set, see Initialization and Authorization Properties.

OLE DB Driver for SQL Server Example

In this example, a data source object is created using the OLE DB Driver for SQL Server, and MARS is enabled using the DBPROPSET_SQLSERVERDBINIT property set before the session object is created.

See Also

© Getty Images Mars exploration: A driver of innovation and commerce

Despite the disruption of so many aspects of life on Earth caused by the COVID-19 pandemic, our nation and the rest of the world continue to be enthralled with, and fully engaged in, the exploration of Mars. Indeed, not one, not two, but three international robotic missions were launched toward Mars this summer. Two of those missions, one from the United Arab Emirates (UAE) and the other from China, launched within four days of each other (July 19 and July 23, respectively), and the United States successfully launched its Mars 2020 rover on July 30th.

America is also planning to send astronauts back to the moon later this decade, followed by sending humans to Mars in the 2030s. Such missions to the Red Planet have the potential to discover whether life ever existed on Mars and will also seek to determine whether humans will be able to live, work and establish a permanent presence on that planet in the future.

There are many reasons that are given for humanity's efforts to explore Mars, ranging from the philosophical to the practical, such as humankind's instinctive passion and need to explore, our innate need to push our boundaries, to answer fundamental questions about our place in the universe or as an alternative home. What is often overlooked, however, are the resulting economic benefits, and the potential new markets that would be created, from such an ambitious undertaking.

In many cases, these are being advanced by the work of major corporations, which employ innumerable people. But just as often, the innovations come from the work of small businesses that are located around the country (and the world). In fact, such innovations and contributions to our economy by companies large and small are already happening (and have been happening for many years). Actual space exploration work is not only being conducted by NASA and by the large aerospace companies but also by small businesses and entrepreneurs, machinists and pipefitters, colleges and other entities.

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The launch industry is but one example. It requires a highly educated and skilled workforce from many different fields and employs thousands in high-paying jobs. This is highlighted in the recently released NASA Economic Impact Report - 2019, which showed that NASA generated over $64 billion in economic output in 2019 resulting in well over 300,000 jobs.

What must be made abundantly clear, however, is that getting humanity to Mars is not solely within the purview and responsibility of large rocket companies. Such companies are clearly essential in achieving this goal. But to send humans to Mars and return them safely - and to create a sustainable human presence on Mars - will require far more than just launch vehicles. It will also require a vast network of expertise and contributions from small, medium and large companies and extraordinary innovation in new technologies (each of which will also be applied to improve life on Earth), that are ordinarily not associated with space exploration.

Small businesses, for example, played a central role in designing and building instruments on the Mars Science Laboratory (MSL) and its Curiosity rover, which touched down on the martian surface in 2012 and is still exploring today.


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Some of the new technologies and innovations that will be required for future human activities on Mars include:

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Environmental Control and Life Support Systems (ECLSS) will need to be greatly improved, both in efficiency and reliability, over what is currently available as we reach further into space. Through innovations designed for Mars, many lessons (and products) could be applied to commercial, private residential or laboratory environmental systems.

Water conservation, reclamation and production is required for a sustainable human presence on Mars. Mars is an arid planet, but there is significant water in the martian regolith and below the surface. Technologies and procedures for extraction, reclamation, and even production of water on Mars will be beneficial on Earth, particularly in arid regions.

Artificial intelligence (AI) has been making major strides in the last several years for terrestrial utilization. But such advancements will probably play a crucial role in our efforts to send humans to Mars. Mars is so far away that it often will take 10-20 minutes for a communication from Earth to reach Mars - and another 10-20 minutes for a reply to reach Earth. Because of this time factor, crews going to Mars will need to be far more self-sufficient and have systems that are smarter and able to help self-diagnose, and in some cases, fix problems that develop with mission systems.

Remote medicine: When astronauts are on the surface of Mars, no emergency medical evacuation will be possible. In addition, as mentioned before, there will be significant delays in direct communication with Earth because of the distance between the Earth and Mars. To remedy this, new methods of utilizing telemedicine and the utilization of intelligent systems (AI) could be the difference between life and death. As these systems are perfected, they could have a tremendous benefit to medical treatment around the world and - as the COVID-19 crisis has shown us - during times of pandemics and quarantine.

3D printing is already being utilized on the International Space Station. This technology will be indispensable for manufacturing space parts, but it may also be used to print food and even human organs if the need arises. As such innovations are made to address the unique situations that exist and may arise in space, these benefits will almost certainly be applied to products here on Earth.

Agriculture is critical to space exploration. For humanity to viably live and work on Mars (or anywhere else away from Earth), we will need to learn how to grow food away from the protection of Earth. In doing so, the processes and technology that would be developed could also be applied to the agricultural and food production industry here on Earth.

Cell grown meat is another technology that could get a substantial boost as we attempt to solve the challenges of living on Mars. While it is extremely unlikely that large animals would be transported to (and could thrive on) Mars at any time in the near future, astronauts and settlers would be able to have fresh meat if this technology could be applied to the deep space and martian environments. Several companies are now creating cell grown meat that in many cases is indistinguishable from meat obtained through traditional methods. Advancing this process for utilization on Mars could enhance and accelerate the market for this type of non-traditional meat production on Earth.

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National and international morale: Space exploration has a unique power to bring people together and inspire the world. As such, when people are optimistic about the future, it usually has a positive impact on the economy. Space exploration is also a human endeavor that transcends partisan politics, nationality and ethnicity, gender and economic class. In an age where we have little to no agreement on so many issues, space exploration is a unifying force that all of us can count on.

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Rick Zucker is vice president for policy at Explore Mars, Inc. Chris Carberry is CEO of Explore Mars, Inc., and author of 'Alcohol in Space.'