backtrace.php

<?php

/**
 * Plugin Name: DB Query Backtrace
 * Description: Add backtraces to MySQL Queries to enable backtracing from mysql slowlogs / process lists.
 * Author: Joe Hoyle
 * Version: 1.0
 */

namespace DB_Query_Backtrace;

add_filter( 'query', __NAMESPACE__ . '\\add_backtrace_to_query', 100 );

/**
 * Inject the backtrace on the end of all queres
 *
 * @param string $query
 * @return string
 */
function add_backtrace_to_query( $query ) {
	/*
	   Backtrace:
	   0: this file
	   1: wp-db.php calling apply filters
	   2: wpdb::query() function call
	   3: wpdb::(get_col/get_var/get_results)
	 */
	$backtrace = array_slice( debug_backtrace( false, 6 ), 4, 1 );

	$call = implode( ', ', array_map( __NAMESPACE__ . '\\backtrace_item_string_value', $backtrace ) );
	var_dump($call);
	return $query . ' # Backtrace: ' . $call;
}

/**
 * Transform an item from debug_backtrace() to a short human readable version.
 *
 * @param  array $backtrace
 * @return string
 */
function backtrace_item_string_value( $backtrace ) {
	return sprintf(
		'%s%s( %s )',
		$backtrace['class'] ? $backtrace['class'] . '::' : '',
		$backtrace['function'],
		implode( ', ', array_map( __NAMESPACE__ . '\\param_string_value', $backtrace['args'] ) )
	);
}

/**
 * Get a human readable string for a param passed to a function.
 *
 * @param  mixed $val
 * @return string
 */
function param_string_value( $val ) {
	if ( is_object( $val ) ) {
		return get_class( $val );
	}
	$val = str_replace( "\n", '', var_export( $val, true ) );

	if ( strlen( $val ) > 100 ) {
		$val = substr( $val, 0, 100 ) . '...';
	}

	return $val;
}