delay_execution.c

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/*-------------------------------------------------------------------------
 *
 * delay_execution.c
 *      Test module to allow delay between parsing and execution of a query.
 *
 * The delay is implemented by taking and immediately releasing a specified
 * advisory lock.  If another process has previously taken that lock, the
 * current process will be blocked until the lock is released; otherwise,
 * there's no effect.  This allows an isolationtester script to reliably
 * test behaviors where some specified action happens in another backend
 * between parsing and execution of any desired query.
 *
 * Copyright (c) 2020-2021, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/test/modules/delay_execution/delay_execution.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <limits.h>
 
#include "optimizer/planner.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/inval.h"
 
 
PG_MODULE_MAGIC;
 
/* GUC: advisory lock ID to use.  Zero disables the feature. */
static int  post_planning_lock_id = 0;
 
/* Save previous planner hook user to be a good citizen */
static planner_hook_type prev_planner_hook = NULL;
 
/* Module load/unload functions */
void        _PG_init(void);
void        _PG_fini(void);
 
 
/* planner_hook function to provide the desired delay */
static PlannedStmt *
delay_execution_planner(Query *parse, const char *query_string,
                        int cursorOptions, ParamListInfo boundParams)
{
    PlannedStmt *result;
 
    /* Invoke the planner, possibly via a previous hook user */
    if (prev_planner_hook)
        result = prev_planner_hook(parse, query_string, cursorOptions,
                                   boundParams);
    else
        result = standard_planner(parse, query_string, cursorOptions,
                                  boundParams);
 
    /* If enabled, delay by taking and releasing the specified lock */
    if (post_planning_lock_id != 0)
    {
        DirectFunctionCall1(pg_advisory_lock_int8,
                            Int64GetDatum((int64) post_planning_lock_id));
        DirectFunctionCall1(pg_advisory_unlock_int8,
                            Int64GetDatum((int64) post_planning_lock_id));
 
        /*
         * Ensure that we notice any pending invalidations, since the advisory
         * lock functions don't do this.
         */
        AcceptInvalidationMessages();
    }
 
    return result;
}
 
/* Module load function */
void
_PG_init(void)
{
    /* Set up the GUC to control which lock is used */
    DefineCustomIntVariable("delay_execution.post_planning_lock_id",
                            "Sets the advisory lock ID to be locked/unlocked after planning.",
                            "Zero disables the delay.",
                            &post_planning_lock_id,
                            0,
                            0, INT_MAX,
                            PGC_USERSET,
                            0,
                            NULL,
                            NULL,
                            NULL);
 
    /* Install our hook */
    prev_planner_hook = planner_hook;
    planner_hook = delay_execution_planner;
}
 
/* Module unload function (pro forma, not used currently) */
void
_PG_fini(void)
{
    planner_hook = prev_planner_hook;
}