What Is Assert in PostgreSQL With Code Example

Assert in PostgreSQL

The PostgreSQL Assert function is an internal debugging tool for developers, not for application use. Its main function is to detect programming flaws by testing for “cannot happen” execution conditions. PostgreSQL code regularly uses assertions to validate the server’s internal status, unlike ereport() and elog(). A failed assertion signals a major server logic issue.

Purpose and Function of Assertions

Error detection in the PostgreSQL C code is the main function of the Assert function. Developers utilize assertions to look for situations that, in their opinion, should never arise during code execution if the code is right. They’re frequently called “cannot happen” circumstances.

Developers can use assertions to check data structure consistency before an operation or pointer non-null status before dereferencing. A failed assertion check indicates a PostgreSQL backend code problem or logical conflict, not a user input or outside circumstances. Unlike other PostgreSQL error-handling mechanisms like ereport() and elog(), this function sets Assert apart.

Internal run-time faults are handled by the macro elog(), whereas user-visible problems are handled by ereport(). A clean-up procedure is started when elog(ERROR) is called, ending the current transaction, and enabling the server process to handle further requests. For foreseeable mistakes like a syntax error or a duplicate key insertion, these are used.

Conversely, assert is for logical errors in the code that are unexpected or surprising. Given that a failed assertion indicates a state that the program’s logic is not ready to handle, the backend process usually ends instantly, frequently with a core dump. This sudden stop makes it easier for developers to locate the bug precisely and in what context.

Enabling and Disabling Assertions

By default, a typical production build of PostgreSQL does not have assertion checks enabled. While building PostgreSQL. They are enabled at compilation time by passing a particular option to the configure script. “-enable-cassert” is the command-line argument. This setting activates a lot of assert() checks in the server code.

Key considerations for enabling assertions include:

Performance Impact: The server may become noticeably slower if assertions are enabled. The reason behind this is that the checks are carried out often while the program is running in order to continuously verify its current condition.

Intended Use: Code development, debugging, and testing PostgreSQL beta versions to find new bugs all benefit greatly from assertions due to their speed overhead. Production situations are not advised to use them.

Compiler Optimization: Deactivating compiler optimizations by changing the environment variable CFLAGS to -O0 is also advised when building with assertions enabled for debugging. When an assertion fails or a debugger is used, this shortens compilation time and more importantly improves the quality of the debugging information that is accessible.

Code Example:

DROP FUNCTION IF EXISTS check_salary(salary numeric);
CREATE OR REPLACE FUNCTION check_salary(salary numeric)
RETURNS text AS $$
BEGIN
    IF salary <= 1000 THEN
        RAISE EXCEPTION 'Assertion failed: salary must be greater than 1000. Got %', salary;
    END IF;

    IF salary > 100000 THEN
        RAISE EXCEPTION 'Assertion failed: salary must not exceed 100000. Got %', salary;
    END IF;

    IF salary = 50000 THEN
        RAISE EXCEPTION 'Assertion failed: salary cannot be exactly 50000';
    END IF;

    RETURN format('All assertions passed. Salary = %s', salary);
END;
$$ LANGUAGE plpgsql;

Output:

DROP FUNCTION
CREATE FUNCTION

Context within the Developer’s Toolkit

For PostgreSQL developers, assertions are a component of a larger set of debugging tools. The following additional are included and have comparable functions:

Debug Print Parameters: The PostgreSQL developer’s Debug Print Parameters reveal query processing’s inner workings. Debug_print_parse, debug_print_rewritten, and debug_print_plan are disabled by default but can be enabled to give extensive debugging output for each query transformation stage. Debug_print_parse prints the parse tree, debug_print_rewritten shows the query rewriter’s output, and debug_print_plan reveals each query’s execution plan. Enabling debug_pretty_print indents this output for greater readability in the server log at the LOG message level.

Profiling: PostgreSQL developers use profiling to assess performance and find which functions take the most time. This feature must be enabled while compiling PostgreSQL . It requires the GCC compiler and the configure script’s –enable-profiling option.

Logging Parameters: PostgreSQL’s logging options give developers significant flexibility over error reporting and performance monitoring for troubleshooting, analyzing, and tweaking database operations. Developers can activate debug_print_parse, debug_print_rewritten, and debug_print_plan to log the complete parse tree, query rewriter output, and query execution plan for each query for in-depth query execution analysis.

Assert is designed to validate logical invariants, which must always be true during execution. A proactive approach to problem detection early in development ensures PostgreSQL codebase integrity and stability. When adding new functionality, developers should consider corner cases and component relationships, where assertions are most effective for avoiding errors.

To sum up, developers working on the PostgreSQL project can use the versatile Assert function as a compile-time debugging tool. Enabled via the enable-cassert configure option, it checks for “cannot happen” circumstances to validate internal programming logic. Because it may detect serious defects, it is a vital tool for testing and development, but because of its large performance impact, it is not appropriate for use in production settings.