citus/src/backend/distributed/planner/multi_planner.c

/*-------------------------------------------------------------------------
 *
 * multi_planner.c
 *	  General Citus planner code.
 *
 * Copyright (c) 2012-2015, Citus Data, Inc.
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <limits.h>

#include "catalog/pg_type.h"

#include "distributed/citus_nodefuncs.h"
#include "distributed/citus_nodes.h"
#include "distributed/metadata_cache.h"
#include "distributed/multi_planner.h"
#include "distributed/multi_logical_optimizer.h"
#include "distributed/multi_logical_planner.h"
#include "distributed/multi_physical_planner.h"
#include "distributed/modify_planner.h"

#include "executor/executor.h"

#include "optimizer/planner.h"

#include "utils/memutils.h"

/* local function forward declarations */
static void CheckNodeIsDumpable(Node *node);


/* local function forward declarations */
static MultiPlan * CreatePhysicalPlan(Query *parse);
static char * GetMultiPlanString(PlannedStmt *result);
static PlannedStmt * MultiQueryContainerNode(PlannedStmt *result, MultiPlan *multiPlan);


/* Distributed planner hook */
PlannedStmt *
multi_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
{
	PlannedStmt *result = NULL;

	/*
	 * First call into standard planner. This is required because the Citus
	 * planner relies on parse tree transformations made by postgres' planner.
	 */
	result = standard_planner(parse, cursorOptions, boundParams);

	if (NeedsDistributedPlanning(parse))
	{
		MultiPlan *physicalPlan = CreatePhysicalPlan(parse);

		/* store required data into the planned statement */
		result = MultiQueryContainerNode(result, physicalPlan);
	}

	return result;
}


/*
 * CreatePhysicalPlan encapsulates the logic needed to transform a particular
 * query into a physical plan. For modifications, queries immediately enter
 * the physical planning stage, since they are essentially "routed" to remote
 * target shards. SELECT queries go through the full logical plan/optimize/
 * physical plan process needed to produce distributed query plans.
 */
static MultiPlan *
CreatePhysicalPlan(Query *parse)
{
	Query *parseCopy = copyObject(parse);
	MultiPlan *physicalPlan = NULL;
	CmdType commandType = parse->commandType;

	if (commandType == CMD_INSERT || commandType == CMD_UPDATE ||
		commandType == CMD_DELETE)
	{
		/* modifications go directly from a query to a physical plan */
		physicalPlan = MultiModifyPlanCreate(parse);
	}
	else
	{
		/* Create and optimize logical plan */
		MultiTreeRoot *logicalPlan = MultiLogicalPlanCreate(parseCopy);
		MultiLogicalPlanOptimize(logicalPlan);

		/*
		 * This check is here to make it likely that all node types used in
		 * Citus are dumpable. Explain can dump logical and physical plans
		 * using the extended outfuncs infrastructure, but it's infeasible to
		 * test most plans. MultiQueryContainerNode always serializes the
		 * physical plan, so there's no need to check that separately.
		 */
		CheckNodeIsDumpable((Node *) logicalPlan);

		/* Create the physical plan */
		physicalPlan = MultiPhysicalPlanCreate(logicalPlan);
	}

	return physicalPlan;
}


/*
 * GetMultiPlan returns the associated MultiPlan for a PlannedStmt if the
 * statement requires distributed execution, NULL otherwise.
 */
MultiPlan *
GetMultiPlan(PlannedStmt *result)
{
	char *serializedMultiPlan = NULL;
	MultiPlan *multiPlan = NULL;

	serializedMultiPlan = GetMultiPlanString(result);
	multiPlan = (MultiPlan *) CitusStringToNode(serializedMultiPlan);
	Assert(CitusIsA(multiPlan, MultiPlan));

	return multiPlan;
}


/* Does the passed in statement require distributed execution? */
bool
HasCitusToplevelNode(PlannedStmt *result)
{
	/*
	 * Can't be a distributed query if the extension hasn't been loaded
	 * yet. Directly return false, part of the required infrastructure for
	 * further checks might not be present.
	 */
	if (!CitusHasBeenLoaded())
	{
		return false;
	}

	if (GetMultiPlanString(result) == NULL)
	{
		return false;
	}
	else
	{
		return true;
	}
}


/*
 * CreateCitusToplevelNode creates the top-level planTree node for a
 * distributed statement. That top-level node is a) recognizable by the
 * executor hooks, allowing them to redirect execution, b) contains the
 * parameters required for distributed execution.
 *
 * The exact representation of the top-level node is an implementation detail
 * which should not be referred to outside this file, as it's likely to become
 * version dependant. Use GetMultiPlan() and HasCitusToplevelNode() to access.
 *
 * Internally the data is stored as arguments to a 'citus_extradata_container'
 * function, which has to be removed from the really executed plan tree before
 * query execution.
 */
static PlannedStmt *
MultiQueryContainerNode(PlannedStmt *result, MultiPlan *multiPlan)
{
	FunctionScan *fauxFunctionScan = NULL;
	RangeTblFunction *fauxFunction = NULL;
	FuncExpr *fauxFuncExpr = NULL;
	Const *multiPlanData = NULL;
	char *serializedPlan = NULL;

	/* pass multiPlan serialized as a constant function argument */
	serializedPlan = CitusNodeToString(multiPlan);
	multiPlanData = makeNode(Const);
	multiPlanData->consttype = CSTRINGOID;
	multiPlanData->constlen = strlen(serializedPlan);
	multiPlanData->constvalue = CStringGetDatum(serializedPlan);
	multiPlanData->constbyval = false;
	multiPlanData->location = -1;

	fauxFuncExpr = makeNode(FuncExpr);
	fauxFuncExpr->funcid = CitusExtraDataContainerFuncId();
	fauxFuncExpr->funcretset = true;
	fauxFuncExpr->location = -1;

	fauxFuncExpr->args = list_make1(multiPlanData);
	fauxFunction = makeNode(RangeTblFunction);
	fauxFunction->funcexpr = (Node *) fauxFuncExpr;

	fauxFunctionScan = makeNode(FunctionScan);
	fauxFunctionScan->functions = lappend(fauxFunctionScan->functions, fauxFunction);

	/*
	 * Add set returning function to target list if the original (postgres
	 * created) plan doesn't support backward scans; doing so prevents
	 * backward scans being supported by the new plantree as well.  This is
	 * ugly as hell, but until we can rely on custom scans (which can signal
	 * this via CUSTOMPATH_SUPPORT_BACKWARD_SCAN), there's not really a pretty
	 * method to achieve this.
	 *
	 * FIXME: This should really be done on the master select plan.
	 */
	if (!ExecSupportsBackwardScan(result->planTree))
	{
		FuncExpr *funcExpr = makeNode(FuncExpr);
		funcExpr->funcretset = true;

		fauxFunctionScan->scan.plan.targetlist =
			lappend(fauxFunctionScan->scan.plan.targetlist,
					funcExpr);
	}

	result->planTree = (Plan *) fauxFunctionScan;

	return result;
}


/*
 * GetMultiPlanString returns either NULL, if the plan is not a distributed
 * one, or the string representing the distributed plan.
 */
static char *
GetMultiPlanString(PlannedStmt *result)
{
	FunctionScan *fauxFunctionScan = NULL;
	RangeTblFunction *fauxFunction = NULL;
	FuncExpr *fauxFuncExpr = NULL;
	Const *multiPlanData = NULL;

	if (!IsA(result->planTree, FunctionScan))
	{
		return NULL;
	}

	fauxFunctionScan = (FunctionScan *) result->planTree;

	if (list_length(fauxFunctionScan->functions) != 1)
	{
		return NULL;
	}

	fauxFunction = linitial(fauxFunctionScan->functions);

	if (!IsA(fauxFunction->funcexpr, FuncExpr))
	{
		return NULL;
	}

	fauxFuncExpr = (FuncExpr *) fauxFunction->funcexpr;

	if (fauxFuncExpr->funcid != CitusExtraDataContainerFuncId())
	{
		return NULL;
	}

	if (list_length(fauxFuncExpr->args) != 1)
	{
		ereport(ERROR, (errmsg("unexpected number of function arguments to "
							   "citus_extradata_container")));
	}

	multiPlanData = (Const *) linitial(fauxFuncExpr->args);
	Assert(IsA(multiPlanData, Const));
	Assert(multiPlanData->consttype == CSTRINGOID);

	return DatumGetCString(multiPlanData->constvalue);
}


/*
 * CheckNodeIsDumpable checks that the passed node can be dumped using
 * CitusNodeToString(). As this checks is expensive, it's only active when
 * assertions are enabled.
 */
static void
CheckNodeIsDumpable(Node *node)
{
#ifdef USE_ASSERT_CHECKING
	char *out = CitusNodeToString(node);
	pfree(out);
#endif
}