Re: [COMMITTERS] pgsql: Create hooks to let a loadable plugin monitor (or even replace)

I was referring to these two:

http://archives.postgresql.org/pgsql-patches/2007-05/msg00431.php and
http://archives.postgresql.org/pgsql-committers/2007-05/msg00315.php
 

This being a community effort, we would expect that.

I also wished to propose to allow the plugin to completely replace (or augment) the plan produced by the planner (by passing in a double-pointer of the plan to the plugin); but I was wary that the idea might get rejected, for being too radical an idea.

In the last version of the planner plugin patch, the plugins were maintained as a list, hence allowing for multiple post-planner-plugins to work one after the other (the variable PPPList); much like the layered I/O driver architecture of Windows' NTFS sans the guarantee of ordering between the plugins. To this we may add the ability to pass on the result plan of one plugin to the next, letting them improve the plan incrementally. Next, we can add string identifiers like I/O drivers to guarantee the order in which the plugins will be executed. But again, maybe we don't need multiple planners working simultaneously ATM.

As for the current patch,I had only a few cosmetic changes in mind:

The comment above planner.c:planner() says '...hook variable that lets a plugin get control before and after the standard planning ...'; but if we look at the code, we are just replacing the call to standard_planner(); we are not calling the plugin before and after standard_planner().

Also, another cosmetic change like reducing an 'if' as follows:

Change:
PlannedStmt *
planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
{
    PlannedStmt *result;

    if (planner_hook)
        result = (*planner_hook) (parse, cursorOptions, boundParams);
    else
        result = standard_planner(parse, cursorOptions, boundParams);
    return result;
}

To:
PlannedStmt *
planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
{
    planner_hook_type planner_func = planner_hook ? planner_hook : standard_planner;

    return (*planner_func) (parse, cursorOptions, boundParams);
}