k6 Postgres plugin: Pagination Parameter Binding Ambiguity

Parameter Binding Behavior

The k6 Postgres plugin preserves the placeholder order exactly as they appear in the SQL string. It does not shift indices to accommodate LIMIT or OFFSET clauses, nor does it treat pagination parameters as special entities. Because the plugin forwards the query and the parameters array to the underlying Go driver, the binding is strictly positional: $1 maps to the first element of the array, $2 to the second, and so on.

Likely Cause of Ambiguity

Binding errors typically occur when developers assume LIMIT and OFFSET are handled separately from the WHERE clause. If your query is structured as SELECT * FROM users WHERE status = $1 LIMIT $2 OFFSET $3, the plugin expects an array of three values in that exact sequence. If you provide only the pagination values, the driver will attempt to bind the limit value to the status filter, leading to runtime type errors or empty result sets.

Steps to Eliminate Binding Errors

1. Strict Positional Mapping: Ensure your parameters array matches the numerical order of the placeholders in the string.
2. Consistent Ordering: Place your pagination placeholders at the end of the query to keep the core business logic parameters (filters) at the start of the array.
3. Avoid Mixing Styles: Do not mix positional placeholders ($1) with named parameters in a single query, as this is not supported and will trigger binding failures.

// Correct implementation for pagination
const query = 'SELECT * FROM logs WHERE level = $1 LIMIT $2 OFFSET $3';
const params = ['ERROR', 10, 50]; // $1=level, $2=limit, $3=offset
const rows = client.query(query, params);

Memory and Streaming Constraints

The k6 Postgres plugin does not currently support streaming for large result sets. Every query() call loads the entire returned dataset into the k6 JavaScript runtime memory. To mitigate memory exhaustion during high-volume pagination tests, you must keep the LIMIT value small and iterate through pages using sequential OFFSET calls across different virtual user (VU) iterations.

Verification

To verify that parameters are binding to the correct columns, run your k6 script with the debug environment variable enabled:

DEBUG=k6:postgres k6 run script.js

Inspect the console output to confirm the final SQL string and the bound parameter array match your expectations.

Diagnostic Detail Needed: If you are still experiencing shifted indices, please provide your current plugin version. Versions prior to v0.5.0 may exhibit different binding behaviors.