Added a config for custom_dimensions_max_length issue-16150

config/global.ini.php

@@ -1100,6 +1100,12 @@
 ; If you define Custom Variables for your visitor, for example set the visit type
 ;Segments[]="customVariableName1==VisitType;customVariableValue1==Customer"
 
+[CustomDimensions]
+; The maximum length for custom dimension values stored in the database.
+; If this value is -1, no truncation will be applied.
+; If the value is too high, it will be capped to 65535.
+custom_dimensions_max_length = 250
+
 [Deletelogs]
 ; delete_logs_enable - enable (1) or disable (0) delete log feature. Make sure that all archives for the given period have been processed (setup a cronjob!),
 ; otherwise you may lose tracking data.

plugins/CustomDimensions/Tracker/CustomDimensionsRequestProcessor.php

@@ -174,7 +174,17 @@ private function getCustomDimensionsInScope($scope, Request $request)
 
     private static function prepareValue($value)
     {
-        return mb_substr(trim($value), 0, 250);
+        $inputMaxLength = 250;
+        // Get the maximum length from the config, defaulting to 250 if not set
+        $maxLengthConfig = intval(\Piwik\Config::getInstance()->CustomDimensions['custom_dimensions_max_length'] ?? $inputMaxLength);
+
+        // Ensure max length is a reasonable number: -1 means no limit, cap at 65535 for TEXT fields
+        if ($maxLengthConfig === -1) {
+            $inputMaxLength = 65535; // No limit, but cap it for safety
+        } else {
+            $inputMaxLength = min($maxLengthConfig, 65535);
+        }
+        return mb_substr(trim($value), 0, $inputMaxLength);
     }
 
     public static function buildCustomDimensionTrackingApiName($idDimensionOrDimension)