15.00 - ALTER METHOD - Teradata Database

Teradata Database SQL Data Definition Language Detailed Topics

prodname
Teradata Database
vrm_release
15.00
category
Programming Reference
featnum
B035-1184-015K

ALTER METHOD

When to Specify Unprotected Mode

To protect the system from new external routines that have not passed your quality metrics, the default execution mode for all external routines is EXECUTE PROTECTED. If the default specification for CREATE METHOD and REPLACE METHOD were EXECUTE NOT PROTECTED, then an error in the created function could crash the system.

Protected mode is a database state that traps on memory address violations, corrupted data structures, and illegal computations, such as divide-by-zero, to ensure they do not crash the system. Protected mode does not detect or protect against CPU and memory loops or operating system I/Os such as opening external files to read from or write to them.

This execution mode isolates all of the data the external routine might access as a separate process, or “server” in its own local work space (see SQL External Routine Programming for details). If any memory violation or other system error occurs, then the error is localized to the routine and the transaction executing it, not the entire database (see “Protected and Unprotected Execution Modes” on page 246 for more information).

Because this isolation also makes the routine run slower, you should change its protection mode to unprotected once it has passed all your quality metrics for being put into production use. You change the execution mode for the routine with a simple ALTER METHOD request (see “ALTER METHOD” on page 20) and specifying the EXECUTE NOT PROTECTED option.

Do not make this change for any method that makes OS system calls. Any such method should always be run in protected or secure mode. You do not need to recompile or relink the external routine after changing its protection mode.

As a rule, the DBA should only specify direct execution mode (assigned by the EXECUTE NOT PROTECTED option) for a method that performs CPU‑only operations after it has been thoroughly debugged. No other user than the DBA, not even the software engineer that writes a UDF, should be granted the privileges to alter it to run in unprotected mode. Never run external routines that cause the OS to consume system resources in unprotected mode. This includes anything that causes the OS to allocate system context, including open files, pipes, semaphores, tokens, threads (processes), and so on.

The following table summarizes how the method protection mode options should be used:

 

IF …

THEN specify …

you are still developing and debugging a method

EXECUTE PROTECTED.

the method opens a file or uses another operating system resource that requires tracking by the operating system

This includes anything that causes the OS to allocate system context, including open files, pipes, semaphores, tokens, threads (processes), and so on.

EXECUTE PROTECTED.

Running such a method in unprotected mode could interfere with the proper operation of the Teradata Database.

the method does not use any operating system resources

EXECUTE NOT PROTECTED.

Running a method in unprotected mode speeds up processing considerably.

Use this option only after thoroughly debugging the method and making sure it produces the correct output.