plancache.c

来自「postgresql8.3.4源码,开源数据库」· C语言 代码 · 共 1,016 行 · 第 1/2 页

/*-------------------------------------------------------------------------
 *
 * plancache.c
 *	  Plan cache management.
 *
 * We can store a cached plan in either fully-planned format, or just
 * parsed-and-rewritten if the caller wishes to postpone planning until
 * actual parameter values are available.  CachedPlanSource has the same
 * contents either way, but CachedPlan contains a list of PlannedStmts
 * and bare utility statements in the first case, or a list of Query nodes
 * in the second case.
 *
 * The plan cache manager itself is principally responsible for tracking
 * whether cached plans should be invalidated because of schema changes in
 * the tables they depend on.  When (and if) the next demand for a cached
 * plan occurs, the query will be replanned.  Note that this could result
 * in an error, for example if a column referenced by the query is no
 * longer present.	The creator of a cached plan can specify whether it
 * is allowable for the query to change output tupdesc on replan (this
 * could happen with "SELECT *" for example) --- if so, it's up to the
 * caller to notice changes and cope with them.
 *
 * Currently, we use only relcache invalidation events to invalidate plans.
 * This means that changes such as modification of a function definition do
 * not invalidate plans using the function.  This is not 100% OK --- for
 * example, changing a SQL function that's been inlined really ought to
 * cause invalidation of the plan that it's been inlined into --- but the
 * cost of tracking additional types of object seems much higher than the
 * gain, so we're just ignoring them for now.
 *
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/utils/cache/plancache.c,v 1.15.2.1 2008/09/15 23:37:49 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "utils/plancache.h"
#include "access/transam.h"
#include "catalog/namespace.h"
#include "executor/executor.h"
#include "optimizer/clauses.h"
#include "storage/lmgr.h"
#include "tcop/pquery.h"
#include "tcop/tcopprot.h"
#include "tcop/utility.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/resowner.h"


typedef struct
{
	void		(*callback) ();
	void	   *arg;
} ScanQueryWalkerContext;

typedef struct
{
	Oid			inval_relid;
	CachedPlan *plan;
} InvalRelidContext;


static List *cached_plans_list = NIL;

static void StoreCachedPlan(CachedPlanSource *plansource, List *stmt_list,
				MemoryContext plan_context);
static List *do_planning(List *querytrees, int cursorOptions);
static void AcquireExecutorLocks(List *stmt_list, bool acquire);
static void AcquirePlannerLocks(List *stmt_list, bool acquire);
static void LockRelid(Oid relid, LOCKMODE lockmode, void *arg);
static void UnlockRelid(Oid relid, LOCKMODE lockmode, void *arg);
static void ScanQueryForRelids(Query *parsetree,
				   void (*callback) (),
				   void *arg);
static bool ScanQueryWalker(Node *node, ScanQueryWalkerContext *context);
static bool rowmark_member(List *rowMarks, int rt_index);
static bool plan_list_is_transient(List *stmt_list);
static void PlanCacheCallback(Datum arg, Oid relid);
static void InvalRelid(Oid relid, LOCKMODE lockmode,
		   InvalRelidContext *context);


/*
 * InitPlanCache: initialize module during InitPostgres.
 *
 * All we need to do is hook into inval.c's callback list.
 */
void
InitPlanCache(void)
{
	CacheRegisterRelcacheCallback(PlanCacheCallback, (Datum) 0);
}

/*
 * CreateCachedPlan: initially create a plan cache entry.
 *
 * The caller must already have successfully parsed/planned the query;
 * about all that we do here is copy it into permanent storage.
 *
 * raw_parse_tree: output of raw_parser()
 * query_string: original query text (can be NULL if not available, but
 *		that is discouraged because it degrades error message quality)
 * commandTag: compile-time-constant tag for query, or NULL if empty query
 * param_types: array of parameter type OIDs, or NULL if none
 * num_params: number of parameters
 * cursor_options: options bitmask that was/will be passed to planner
 * stmt_list: list of PlannedStmts/utility stmts, or list of Query trees
 * fully_planned: are we caching planner or rewriter output?
 * fixed_result: TRUE to disallow changes in result tupdesc
 */
CachedPlanSource *
CreateCachedPlan(Node *raw_parse_tree,
				 const char *query_string,
				 const char *commandTag,
				 Oid *param_types,
				 int num_params,
				 int cursor_options,
				 List *stmt_list,
				 bool fully_planned,
				 bool fixed_result)
{
	CachedPlanSource *plansource;
	OverrideSearchPath *search_path;
	MemoryContext source_context;
	MemoryContext oldcxt;

	/*
	 * Make a dedicated memory context for the CachedPlanSource and its
	 * subsidiary data.  We expect it can be pretty small.
	 */
	source_context = AllocSetContextCreate(CacheMemoryContext,
										   "CachedPlanSource",
										   ALLOCSET_SMALL_MINSIZE,
										   ALLOCSET_SMALL_INITSIZE,
										   ALLOCSET_SMALL_MAXSIZE);

	/*
	 * Fetch current search_path into new context, but do any recalculation
	 * work required in caller's context.
	 */
	search_path = GetOverrideSearchPath(source_context);

	/*
	 * Create and fill the CachedPlanSource struct within the new context.
	 */
	oldcxt = MemoryContextSwitchTo(source_context);
	plansource = (CachedPlanSource *) palloc(sizeof(CachedPlanSource));
	plansource->raw_parse_tree = copyObject(raw_parse_tree);
	plansource->query_string = query_string ? pstrdup(query_string) : NULL;
	plansource->commandTag = commandTag;		/* no copying needed */
	if (num_params > 0)
	{
		plansource->param_types = (Oid *) palloc(num_params * sizeof(Oid));
		memcpy(plansource->param_types, param_types, num_params * sizeof(Oid));
	}
	else
		plansource->param_types = NULL;
	plansource->num_params = num_params;
	plansource->cursor_options = cursor_options;
	plansource->fully_planned = fully_planned;
	plansource->fixed_result = fixed_result;
	plansource->search_path = search_path;
	plansource->generation = 0; /* StoreCachedPlan will increment */
	plansource->resultDesc = PlanCacheComputeResultDesc(stmt_list);
	plansource->plan = NULL;
	plansource->context = source_context;
	plansource->orig_plan = NULL;

	/*
	 * Copy the current output plans into the plancache entry.
	 */
	StoreCachedPlan(plansource, stmt_list, NULL);

	/*
	 * Now we can add the entry to the list of cached plans.  The List nodes
	 * live in CacheMemoryContext.
	 */
	MemoryContextSwitchTo(CacheMemoryContext);

	cached_plans_list = lappend(cached_plans_list, plansource);

	MemoryContextSwitchTo(oldcxt);

	return plansource;
}

/*
 * FastCreateCachedPlan: create a plan cache entry with minimal data copying.
 *
 * For plans that aren't expected to live very long, the copying overhead of
 * CreateCachedPlan is annoying.  We provide this variant entry point in which
 * the caller has already placed all the data in a suitable memory context.
 * The source data and completed plan are in the same context, since this
 * avoids extra copy steps during plan construction.  If the query ever does
 * need replanning, we'll generate a separate new CachedPlan at that time, but
 * the CachedPlanSource and the initial CachedPlan share the caller-provided
 * context and go away together when neither is needed any longer.	(Because
 * the parser and planner generate extra cruft in addition to their real
 * output, this approach means that the context probably contains a bunch of
 * useless junk as well as the useful trees.  Hence, this method is a
 * space-for-time tradeoff, which is worth making for plans expected to be
 * short-lived.)
 *
 * raw_parse_tree, query_string, param_types, and stmt_list must reside in the
 * given context, which must have adequate lifespan (recommendation: make it a
 * child of CacheMemoryContext).  Otherwise the API is the same as
 * CreateCachedPlan.
 */
CachedPlanSource *
FastCreateCachedPlan(Node *raw_parse_tree,
					 char *query_string,
					 const char *commandTag,
					 Oid *param_types,
					 int num_params,
					 int cursor_options,
					 List *stmt_list,
					 bool fully_planned,
					 bool fixed_result,
					 MemoryContext context)
{
	CachedPlanSource *plansource;
	OverrideSearchPath *search_path;
	MemoryContext oldcxt;

	/*
	 * Fetch current search_path into given context, but do any recalculation
	 * work required in caller's context.
	 */
	search_path = GetOverrideSearchPath(context);

	/*
	 * Create and fill the CachedPlanSource struct within the given context.
	 */
	oldcxt = MemoryContextSwitchTo(context);
	plansource = (CachedPlanSource *) palloc(sizeof(CachedPlanSource));
	plansource->raw_parse_tree = raw_parse_tree;
	plansource->query_string = query_string;
	plansource->commandTag = commandTag;		/* no copying needed */
	plansource->param_types = param_types;
	plansource->num_params = num_params;
	plansource->cursor_options = cursor_options;
	plansource->fully_planned = fully_planned;
	plansource->fixed_result = fixed_result;
	plansource->search_path = search_path;
	plansource->generation = 0; /* StoreCachedPlan will increment */
	plansource->resultDesc = PlanCacheComputeResultDesc(stmt_list);
	plansource->plan = NULL;
	plansource->context = context;
	plansource->orig_plan = NULL;

	/*
	 * Store the current output plans into the plancache entry.
	 */
	StoreCachedPlan(plansource, stmt_list, context);

	/*
	 * Since the context is owned by the CachedPlan, advance its refcount.
	 */
	plansource->orig_plan = plansource->plan;
	plansource->orig_plan->refcount++;

	/*
	 * Now we can add the entry to the list of cached plans.  The List nodes
	 * live in CacheMemoryContext.
	 */
	MemoryContextSwitchTo(CacheMemoryContext);

	cached_plans_list = lappend(cached_plans_list, plansource);

	MemoryContextSwitchTo(oldcxt);

	return plansource;
}

/*
 * StoreCachedPlan: store a built or rebuilt plan into a plancache entry.
 *
 * Common subroutine for CreateCachedPlan and RevalidateCachedPlan.
 */
static void
StoreCachedPlan(CachedPlanSource *plansource,
				List *stmt_list,
				MemoryContext plan_context)
{
	CachedPlan *plan;
	MemoryContext oldcxt;

	if (plan_context == NULL)
	{
		/*
		 * Make a dedicated memory context for the CachedPlan and its
		 * subsidiary data.  It's probably not going to be large, but just in
		 * case, use the default maxsize parameter.
		 */
		plan_context = AllocSetContextCreate(CacheMemoryContext,
											 "CachedPlan",
											 ALLOCSET_SMALL_MINSIZE,
											 ALLOCSET_SMALL_INITSIZE,
											 ALLOCSET_DEFAULT_MAXSIZE);

		/*
		 * Copy supplied data into the new context.
		 */
		oldcxt = MemoryContextSwitchTo(plan_context);

		stmt_list = (List *) copyObject(stmt_list);
	}
	else
	{
		/* Assume subsidiary data is in the given context */
		oldcxt = MemoryContextSwitchTo(plan_context);
	}

	/*
	 * Create and fill the CachedPlan struct within the new context.
	 */
	plan = (CachedPlan *) palloc(sizeof(CachedPlan));
	plan->stmt_list = stmt_list;
	plan->fully_planned = plansource->fully_planned;
	plan->dead = false;
	if (plansource->fully_planned && plan_list_is_transient(stmt_list))
	{
		Assert(TransactionIdIsNormal(TransactionXmin));
		plan->saved_xmin = TransactionXmin;
	}
	else
		plan->saved_xmin = InvalidTransactionId;
	plan->refcount = 1;			/* for the parent's link */
	plan->generation = ++(plansource->generation);
	plan->context = plan_context;

	Assert(plansource->plan == NULL);
	plansource->plan = plan;

	MemoryContextSwitchTo(oldcxt);
}

/*
 * DropCachedPlan: destroy a cached plan.
 *
 * Actually this only destroys the CachedPlanSource: the referenced CachedPlan
 * is released, but not destroyed until its refcount goes to zero.	That
 * handles the situation where DropCachedPlan is called while the plan is
 * still in use.
 */
void
DropCachedPlan(CachedPlanSource *plansource)
{
	/* Validity check that we were given a CachedPlanSource */
	Assert(list_member_ptr(cached_plans_list, plansource));

	/* Remove it from the list */
	cached_plans_list = list_delete_ptr(cached_plans_list, plansource);

	/* Decrement child CachePlan's refcount and drop if no longer needed */
	if (plansource->plan)
		ReleaseCachedPlan(plansource->plan, false);

	/*
	 * If CachedPlanSource has independent storage, just drop it.  Otherwise
	 * decrement the refcount on the CachePlan that owns the storage.
	 */
	if (plansource->orig_plan == NULL)
	{
		/* Remove the CachedPlanSource and all subsidiary data */
		MemoryContextDelete(plansource->context);
	}
	else
	{
		Assert(plansource->context == plansource->orig_plan->context);
		ReleaseCachedPlan(plansource->orig_plan, false);
	}
}

/*
 * RevalidateCachedPlan: prepare for re-use of a previously cached plan.
 *
 * What we do here is re-acquire locks and rebuild the plan if necessary.
 * On return, the plan is valid and we have sufficient locks to begin
 * execution (or planning, if not fully_planned).
 *
 * On return, the refcount of the plan has been incremented; a later
 * ReleaseCachedPlan() call is expected.  The refcount has been reported
 * to the CurrentResourceOwner if useResOwner is true.
 *
 * Note: if any replanning activity is required, the caller's memory context
 * is used for that work.
 */
CachedPlan *
RevalidateCachedPlan(CachedPlanSource *plansource, bool useResOwner)
{
	CachedPlan *plan;

	/* Validity check that we were given a CachedPlanSource */
	Assert(list_member_ptr(cached_plans_list, plansource));

	/*
	 * If the plan currently appears valid, acquire locks on the referenced
	 * objects; then check again.  We need to do it this way to cover the race
	 * condition that an invalidation message arrives before we get the lock.
	 */
	plan = plansource->plan;
	if (plan && !plan->dead)
	{
		/*
		 * Plan must have positive refcount because it is referenced by
		 * plansource; so no need to fear it disappears under us here.
		 */
		Assert(plan->refcount > 0);

		if (plan->fully_planned)
			AcquireExecutorLocks(plan->stmt_list, true);
		else
			AcquirePlannerLocks(plan->stmt_list, true);

		/*
		 * If plan was transient, check to see if TransactionXmin has
		 * advanced, and if so invalidate it.
		 */
		if (!plan->dead &&
			TransactionIdIsValid(plan->saved_xmin) &&
			!TransactionIdEquals(plan->saved_xmin, TransactionXmin))
			plan->dead = true;

		/*
		 * By now, if any invalidation has happened, PlanCacheCallback will
		 * have marked the plan dead.
		 */
		if (plan->dead)
		{
			/* Ooops, the race case happened.  Release useless locks. */
			if (plan->fully_planned)
				AcquireExecutorLocks(plan->stmt_list, false);
			else
				AcquirePlannerLocks(plan->stmt_list, false);
		}
	}

	/*
	 * If plan has been invalidated, unlink it from the parent and release it.
	 */
	if (plan && plan->dead)
	{
		plansource->plan = NULL;
		ReleaseCachedPlan(plan, false);
		plan = NULL;
	}

	/*
	 * Build a new plan if needed.
	 */
	if (!plan)
	{
		List	   *slist;
		TupleDesc	resultDesc;

		/*
		 * Restore the search_path that was in use when the plan was made.
		 * (XXX is there anything else we really need to restore?)
		 */
		PushOverrideSearchPath(plansource->search_path);

		/*
		 * Run parse analysis and rule rewriting.  The parser tends to
		 * scribble on its input, so we must copy the raw parse tree to
		 * prevent corruption of the cache.  Note that we do not use
		 * parse_analyze_varparams(), assuming that the caller never wants the
		 * parameter types to change from the original values.
		 */
		slist = pg_analyze_and_rewrite(copyObject(plansource->raw_parse_tree),
									   plansource->query_string,
									   plansource->param_types,
									   plansource->num_params);

		if (plansource->fully_planned)
		{
			/* Generate plans for queries */
			slist = do_planning(slist, plansource->cursor_options);
		}

		/*
		 * Check or update the result tupdesc.	XXX should we use a weaker
		 * condition than equalTupleDescs() here?
		 */
		resultDesc = PlanCacheComputeResultDesc(slist);
		if (resultDesc == NULL && plansource->resultDesc == NULL)
		{
			/* OK, doesn't return tuples */
		}
		else if (resultDesc == NULL || plansource->resultDesc == NULL ||
				 !equalTupleDescs(resultDesc, plansource->resultDesc))
		{
			MemoryContext oldcxt;

			/* can we give a better error message? */
			if (plansource->fixed_result)
				ereport(ERROR,
						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
						 errmsg("cached plan must not change result type")));
			oldcxt = MemoryContextSwitchTo(plansource->context);
			if (resultDesc)
				resultDesc = CreateTupleDescCopy(resultDesc);