The patch adresses the TODO list item "Allow external interfaces to
extend the GUC variable set". Plugin modules like the pl<lang> modules needs a way to declare configuration parameters. The postmaster has no knowledge of such modules when it reads the postgresql.conf file. Rather than allowing totally unknown configuration parameters, the concept of a variable "class" is introduced. Variables that belongs to a declared classes will create a placeholder value of string type and will not generate an error. When a module is loaded, it will declare variables for such a class and make those variables "consume" any placeholders that has been defined. Finally, the module will generate warnings for unrecognized placeholders defined for its class. More detail: The design is outlined after the suggestions made by Tom Lane and Joe Conway in this thread: http://archives.postgresql.org/pgsql-hackers/2004-02/msg00229.php A new string variable 'custom_variable_classes' is introduced. This variable is a comma separated string of identifiers. Each identifier denots a 'class' that will allow its members to be added without error. This variable must be defined in postmaster.conf. The lexer (guc_file.l) is changed so that it can accept a qualified name in the form <ID>.<ID> as the name of a variable. I also changed so that the 'custom_variable_classes', if found, is added first of all variables in order to remove the order of declaration issue. The guc_variables table is made more dynamic. It is originally created with 20% slack and can grow dynamically. A capacity is introduced to avoid resizing every time a new variable is added. guc_variables and num_guc_variables becomes static (hidden). The GucInfoMain now uses the new function get_guc_variables() and GetNumConfigOptions instead or using the guc_variables directly. The find_option() function, when passed a missing name, will check if the name is qualified. If the name is qualified and if the qualifier denotes a class included in the 'custom_variable_classes', a placeholder variable will be created. Such a placeholder will not participate in a list operation but will otherwise function as a normal string variable. Define<type>GucVariable() functions will be added, one for each variable type. They are inteded to be used by add-on modules like the pl<lang> mappings. Example: extern void DefineCustomBoolVariable( const char* name, const char* short_desc, const char* long_desc, bool* valueAddr, GucContext context, GucBoolAssignHook assign_hook, GucShowHook show_hook); (I created typedefs for the assign-hook and show-hook functions). A call to these functions will define a new GUC-variable. If a placeholder exists it will be replaced but it's value will be used in place of the default value. The valueAddr is assumed ot point at a default value when the define function is called. The only constraint that is imposed on a Custom variable is that its name is qualified. Finally, a function: void EmittWarningsOnPlacholders(const char* className) was added. This function should be called when a module has completed its variable definitions. At that time, no placeholders should remain for the class that the module uses. If they do, elog(INFO, ...) messages will be issued to inform the user that unrecognized variables are present. Thomas Hallgren
Showing
This diff is collapsed.
Please register or sign in to comment