7.3.6. Effect of Connection & Statement Options
The autocommit option is set at the connection level and affects every statement executed after it being set. Setting the option does not communicate itself with the server and is therefore fast.
Autocommit is on by default. Autocommitting SELECT statements are executed with read committed isolation. This is appropriate since any update based on the autocommitting read would be in a different transaction and hence would block to wait for access to the selected row. Also re-evaluating a select in autocommit mode would read the data in a different transaction. Hence there is no point in repeatable read isolation for autocommitting cursors. Cursors inside procedures have the normal repeatable read isolation regardless of whether the procedure was called in autocommit mode.
When an autocommitting statement starts it is executed in the transaction That is the connection's current transaction when it is received. Before starting the autocommitting statement sets the connection's current transaction to a new one. In this manner a client can issue multiple asynchronous autocommitting statements at the same time and the statements will execute concurrently, each in its own transaction.
If array parameters are used in a statement on an autocommitting connection each parameter row will be processed in its own transaction in sequential order. Multiple Asynchronous statements must be used to execute one client's statements in parallel.
To commit or roll back a transaction in manual-commit mode, an application should call SQLEndTran. Applications should not attempt to commit or roll back transactions by executing COMMIT or ROLLBACK statements with SQLExecute or SQLExecDirect. The effects of doing this are undefined.
This option allows all the values defined in ODBC,
The isolation of an operation is the property of the operation rather than of the transaction within which it takes place. Once an operation has started, e.g. a cursor has been opened, its isolation cannot be changed.
The value of this option will affect any subsequently executed statement. Note that setting this option to different values during a transaction will work, thus a transaction can have cursors with different isolations although that is presumably not the intention of the ODBC specification.
See the transaction model for a definition of the different isolation levels.
A statement in autocommit mode executes in the same transaction as the previous statement. The transaction is committed when the statement successfully completes. The next statement in the connection will execute in the fresh transaction that was associated to the connection at the start of the previous autocommitting statement.
As a consequence of this multiple concurrent autocommitting transactions may execute on the same connection at the same time.
Statements executed with array parameters execute each set of parameters as a separate transaction if the connection is in autocommit mode.
This has the effect of reversing any SQL_CONCUR_LOCK concurrency to SQL_CONCUR_READ_ONLY. The statement option's value is not changed though.
This sets or gets the current qualifier. The initial value is obtained from the server at connect time. The values reflect the effects of any USE statements.
This has the same effect as the NO_CHAR_C_ESCAPE option in the SET statement. It takes boolean int values (0/non-0)
This has the same effect as the CHARSET option in SET statement. It takes string values (the name of the character set to use).
Usable only with the Virtuoso CLI (because the ODBC/iODBC driver manager does not pass-through the custom options to the driver on SQLConnect/SQLDriverConnect). When set to the string "1" means use SSL but no X509 certificates. Setting it to a NULL (default) means no encryption of the ODBC connection. Any other string is treated as a file name of one PKCS12 package to get the data from for establishing an encrypted SSL connection using X509 certificates (see the -E/-X ISQL options).
Usable only with the Virtuoso CLI (because the ODBC/iODBC driver manager does not pass through the custom options to the driver on SQLConnect/SQLDriverConnect). Shuts down the server on connection after authenticating the DBA user (see the -K ISQL option).
SQLSetStmtOption Statement Options
Virtuoso supports all ODBC 2.x and ODBC 3.x statement options. The following options are mentioned below due to implementation specific details.
The supported values are SQL_CONCUR_READ_ONLY, SQL_CONCUR_LOCK and SQL_CONCUR_VALUES, the last option is only available for scrollable cursors. A select statement with SQL_CONCUR_READ_ONLY will make shared locks when locking for repeatable read or serializable transactions. The SQL_CONCUR_LOCK for a select statement will cause it to make exclusive locks, as if it had the FOR UPDATE clause specified.
See the section on scrollable cursors for the effect of SQL_CONCUR_VALUES. For all statements except scrollable cursors this value reverts to SQL_CONCUR_READ_ONLY.
Any searched update or delete statements will make exclusive locks in all cases.
This option only affects static cursors.
This is an extension that allows setting a time limit on the current transaction. The time limit starts at the execution of the statement specifying this option. The transaction will terminate the indicated number of seconds after the execute whether the statement has completed or not.
This is an extension option that controls how many rows of a forward only cursor are prefetched by the execute and fetch calls. A high value is advantageous for long consecutive reads since it cuts down on the number of client server messages exchanged. On the other hand a large value can result in unnecessary data transfer and locking if only the first few rows of a cursor are fetched. A value of -1 will cause the entire rowset to be fetched at the execute, so that no matter the select size, only one message is exchanged. The default value is 20. This can also be set in the virtuoso.ini file.
A select with array parameters will always work as with a SQL_PREFETCH_SIZE of -1, meaning that all the result sets are computed and sent to the client by the SQLExecute call that opens the cursor.
The cursor type options should be set before preparing a statement. Other options may be set at any time. The rowset and prefetch options should not be modified after executing a SELECT.
This is an extension that returns the last assigned identity column value. The return buffer pvParam is of type SQLINTEGER. For this to be meaningful, the statement in question must be an INSERT into a table that has an identity column. Note that if there are more than one identity columns or if triggers make inserts with identity columns the value will be undefined.