plancat.c

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/*-------------------------------------------------------------------------
 *
 * plancat.c
 *	   routines for accessing the system catalogs
 *
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/optimizer/util/plancat.c,v 1.140.2.1 2008/04/01 00:48:44 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <math.h>

#include "access/genam.h"
#include "access/heapam.h"
#include "access/transam.h"
#include "catalog/pg_inherits.h"
#include "nodes/makefuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/plancat.h"
#include "optimizer/predtest.h"
#include "optimizer/prep.h"
#include "parser/parse_expr.h"
#include "parser/parse_relation.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteManip.h"
#include "utils/fmgroids.h"
#include "utils/lsyscache.h"
#include "utils/relcache.h"
#include "utils/syscache.h"
#include "catalog/catalog.h"
#include "miscadmin.h"


/* GUC parameter */
bool		constraint_exclusion = false;

/* Hook for plugins to get control in get_relation_info() */
get_relation_info_hook_type get_relation_info_hook = NULL;


static void estimate_rel_size(Relation rel, int32 *attr_widths,
				  BlockNumber *pages, double *tuples);
static List *get_relation_constraints(PlannerInfo *root,
						 Oid relationObjectId, RelOptInfo *rel,
						 bool include_notnull);


/*
 * get_relation_info -
 *	  Retrieves catalog information for a given relation.
 *
 * Given the Oid of the relation, return the following info into fields
 * of the RelOptInfo struct:
 *
 *	min_attr	lowest valid AttrNumber
 *	max_attr	highest valid AttrNumber
 *	indexlist	list of IndexOptInfos for relation's indexes
 *	pages		number of pages
 *	tuples		number of tuples
 *
 * Also, initialize the attr_needed[] and attr_widths[] arrays.  In most
 * cases these are left as zeroes, but sometimes we need to compute attr
 * widths here, and we may as well cache the results for costsize.c.
 *
 * If inhparent is true, all we need to do is set up the attr arrays:
 * the RelOptInfo actually represents the appendrel formed by an inheritance
 * tree, and so the parent rel's physical size and index information isn't
 * important for it.
 */
void
get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
				  RelOptInfo *rel)
{
	Index		varno = rel->relid;
	Relation	relation;
	bool		hasindex;
	List	   *indexinfos = NIL;

	/*
	 * We need not lock the relation since it was already locked, either by
	 * the rewriter or when expand_inherited_rtentry() added it to the query's
	 * rangetable.
	 */
	relation = heap_open(relationObjectId, NoLock);

	rel->min_attr = FirstLowInvalidHeapAttributeNumber + 1;
	rel->max_attr = RelationGetNumberOfAttributes(relation);

	Assert(rel->max_attr >= rel->min_attr);
	rel->attr_needed = (Relids *)
		palloc0((rel->max_attr - rel->min_attr + 1) * sizeof(Relids));
	rel->attr_widths = (int32 *)
		palloc0((rel->max_attr - rel->min_attr + 1) * sizeof(int32));

	/*
	 * Estimate relation size --- unless it's an inheritance parent, in which
	 * case the size will be computed later in set_append_rel_pathlist, and we
	 * must leave it zero for now to avoid bollixing the total_table_pages
	 * calculation.
	 */
	if (!inhparent)
		estimate_rel_size(relation, rel->attr_widths - rel->min_attr,
						  &rel->pages, &rel->tuples);

	/*
	 * Make list of indexes.  Ignore indexes on system catalogs if told to.
	 * Don't bother with indexes for an inheritance parent, either.
	 */
	if (inhparent ||
		(IgnoreSystemIndexes && IsSystemClass(relation->rd_rel)))
		hasindex = false;
	else
		hasindex = relation->rd_rel->relhasindex;

	if (hasindex)
	{
		List	   *indexoidlist;
		ListCell   *l;
		LOCKMODE	lmode;

		indexoidlist = RelationGetIndexList(relation);

		/*
		 * For each index, we get the same type of lock that the executor will
		 * need, and do not release it.  This saves a couple of trips to the
		 * shared lock manager while not creating any real loss of
		 * concurrency, because no schema changes could be happening on the
		 * index while we hold lock on the parent rel, and neither lock type
		 * blocks any other kind of index operation.
		 */
		if (rel->relid == root->parse->resultRelation)
			lmode = RowExclusiveLock;
		else
			lmode = AccessShareLock;

		foreach(l, indexoidlist)
		{
			Oid			indexoid = lfirst_oid(l);
			Relation	indexRelation;
			Form_pg_index index;
			IndexOptInfo *info;
			int			ncolumns;
			int			i;

			/*
			 * Extract info from the relation descriptor for the index.
			 */
			indexRelation = index_open(indexoid, lmode);
			index = indexRelation->rd_index;

			/*
			 * Ignore invalid indexes, since they can't safely be used for
			 * queries.  Note that this is OK because the data structure we
			 * are constructing is only used by the planner --- the executor
			 * still needs to insert into "invalid" indexes!
			 */
			if (!index->indisvalid)
			{
				index_close(indexRelation, NoLock);
				continue;
			}

			/*
			 * If the index is valid, but cannot yet be used, ignore it; but
			 * mark the plan we are generating as transient. See
			 * src/backend/access/heap/README.HOT for discussion.
			 */
			if (index->indcheckxmin &&
				!TransactionIdPrecedes(HeapTupleHeaderGetXmin(indexRelation->rd_indextuple->t_data),
									   TransactionXmin))
			{
				root->glob->transientPlan = true;
				index_close(indexRelation, NoLock);
				continue;
			}

			info = makeNode(IndexOptInfo);

			info->indexoid = index->indexrelid;
			info->rel = rel;
			info->ncolumns = ncolumns = index->indnatts;

			/*
			 * Allocate per-column info arrays.  To save a few palloc cycles
			 * we allocate all the Oid-type arrays in one request.	Note that
			 * the opfamily array needs an extra, terminating zero at the end.
			 * We pre-zero the ordering info in case the index is unordered.
			 */
			info->indexkeys = (int *) palloc(sizeof(int) * ncolumns);
			info->opfamily = (Oid *) palloc0(sizeof(Oid) * (4 * ncolumns + 1));
			info->opcintype = info->opfamily + (ncolumns + 1);
			info->fwdsortop = info->opcintype + ncolumns;
			info->revsortop = info->fwdsortop + ncolumns;
			info->nulls_first = (bool *) palloc0(sizeof(bool) * ncolumns);

			for (i = 0; i < ncolumns; i++)
			{
				info->indexkeys[i] = index->indkey.values[i];
				info->opfamily[i] = indexRelation->rd_opfamily[i];
				info->opcintype[i] = indexRelation->rd_opcintype[i];
			}

			info->relam = indexRelation->rd_rel->relam;
			info->amcostestimate = indexRelation->rd_am->amcostestimate;
			info->amoptionalkey = indexRelation->rd_am->amoptionalkey;
			info->amsearchnulls = indexRelation->rd_am->amsearchnulls;

			/*
			 * Fetch the ordering operators associated with the index, if any.
			 * We expect that all ordering-capable indexes use btree's
			 * strategy numbers for the ordering operators.
			 */
			if (indexRelation->rd_am->amcanorder)
			{
				int			nstrat = indexRelation->rd_am->amstrategies;

				for (i = 0; i < ncolumns; i++)
				{
					int16		opt = indexRelation->rd_indoption[i];
					int			fwdstrat;
					int			revstrat;

					if (opt & INDOPTION_DESC)
					{
						fwdstrat = BTGreaterStrategyNumber;
						revstrat = BTLessStrategyNumber;
					}
					else
					{
						fwdstrat = BTLessStrategyNumber;
						revstrat = BTGreaterStrategyNumber;
					}

					/*
					 * Index AM must have a fixed set of strategies for it to
					 * make sense to specify amcanorder, so we need not allow
					 * the case amstrategies == 0.
					 */
					if (fwdstrat > 0)
					{
						Assert(fwdstrat <= nstrat);
						info->fwdsortop[i] = indexRelation->rd_operator[i * nstrat + fwdstrat - 1];
					}
					if (revstrat > 0)
					{
						Assert(revstrat <= nstrat);
						info->revsortop[i] = indexRelation->rd_operator[i * nstrat + revstrat - 1];
					}
					info->nulls_first[i] = (opt & INDOPTION_NULLS_FIRST) != 0;
				}
			}

			/*
			 * Fetch the index expressions and predicate, if any.  We must
			 * modify the copies we obtain from the relcache to have the
			 * correct varno for the parent relation, so that they match up
			 * correctly against qual clauses.
			 */
			info->indexprs = RelationGetIndexExpressions(indexRelation);
			info->indpred = RelationGetIndexPredicate(indexRelation);
			if (info->indexprs && varno != 1)
				ChangeVarNodes((Node *) info->indexprs, 1, varno, 0);
			if (info->indpred && varno != 1)
				ChangeVarNodes((Node *) info->indpred, 1, varno, 0);
			info->predOK = false;		/* set later in indxpath.c */
			info->unique = index->indisunique;

			/*
			 * Estimate the index size.  If it's not a partial index, we lock
			 * the number-of-tuples estimate to equal the parent table; if it
			 * is partial then we have to use the same methods as we would for
			 * a table, except we can be sure that the index is not larger
			 * than the table.
			 */
			if (info->indpred == NIL)
			{
				info->pages = RelationGetNumberOfBlocks(indexRelation);
				info->tuples = rel->tuples;
			}
			else
			{
				estimate_rel_size(indexRelation, NULL,
								  &info->pages, &info->tuples);
				if (info->tuples > rel->tuples)
					info->tuples = rel->tuples;
			}

			index_close(indexRelation, NoLock);

			indexinfos = lcons(info, indexinfos);
		}

		list_free(indexoidlist);
	}

	rel->indexlist = indexinfos;

	heap_close(relation, NoLock);

	/*
	 * Allow a plugin to editorialize on the info we obtained from the
	 * catalogs.  Actions might include altering the assumed relation size,
	 * removing an index, or adding a hypothetical index to the indexlist.
	 */
	if (get_relation_info_hook)
		(*get_relation_info_hook) (root, relationObjectId, inhparent, rel);
}

/*
 * estimate_rel_size - estimate # pages and # tuples in a table or index
 *
 * If attr_widths isn't NULL, it points to the zero-index entry of the
 * relation's attr_width[] cache; we fill this in if we have need to compute
 * the attribute widths for estimation purposes.
 */
static void
estimate_rel_size(Relation rel, int32 *attr_widths,
				  BlockNumber *pages, double *tuples)
{
	BlockNumber curpages;
	BlockNumber relpages;
	double		reltuples;
	double		density;

	switch (rel->rd_rel->relkind)
	{
		case RELKIND_RELATION:
		case RELKIND_INDEX:
		case RELKIND_TOASTVALUE:
			/* it has storage, ok to call the smgr */
			curpages = RelationGetNumberOfBlocks(rel);

			/*
			 * HACK: if the relation has never yet been vacuumed, use a
			 * minimum estimate of 10 pages.  This emulates a desirable aspect
			 * of pre-8.0 behavior, which is that we wouldn't assume a newly
			 * created relation is really small, which saves us from making
			 * really bad plans during initial data loading.  (The plans are
			 * not wrong when they are made, but if they are cached and used
			 * again after the table has grown a lot, they are bad.) It would
			 * be better to force replanning if the table size has changed a
			 * lot since the plan was made ... but we don't currently have any
			 * infrastructure for redoing cached plans at all, so we have to
			 * kluge things here instead.
			 *
			 * We approximate "never vacuumed" by "has relpages = 0", which
			 * means this will also fire on genuinely empty relations.	Not
			 * great, but fortunately that's a seldom-seen case in the real
			 * world, and it shouldn't degrade the quality of the plan too
			 * much anyway to err in this direction.
			 */
			if (curpages < 10 && rel->rd_rel->relpages == 0)
				curpages = 10;

			/* report estimated # pages */
			*pages = curpages;
			/* quick exit if rel is clearly empty */
			if (curpages == 0)
			{
				*tuples = 0;
				break;
			}
			/* coerce values in pg_class to more desirable types */
			relpages = (BlockNumber) rel->rd_rel->relpages;
			reltuples = (double) rel->rd_rel->reltuples;

			/*
			 * If it's an index, discount the metapage.  This is a kluge
			 * because it assumes more than it ought to about index contents;
			 * it's reasonably OK for btrees but a bit suspect otherwise.
			 */
			if (rel->rd_rel->relkind == RELKIND_INDEX &&
				relpages > 0)
			{
				curpages--;
				relpages--;
			}
			/* estimate number of tuples from previous tuple density */
			if (relpages > 0)
				density = reltuples / (double) relpages;
			else
			{
				/*
				 * When we have no data because the relation was truncated,
				 * estimate tuple width from attribute datatypes.  We assume
				 * here that the pages are completely full, which is OK for
				 * tables (since they've presumably not been VACUUMed yet) but
				 * is probably an overestimate for indexes.  Fortunately
				 * get_relation_info() can clamp the overestimate to the
				 * parent table's size.
				 *
				 * Note: this code intentionally disregards alignment
				 * considerations, because (a) that would be gilding the lily
				 * considering how crude the estimate is, and (b) it creates
				 * platform dependencies in the default plans which are kind
				 * of a headache for regression testing.
				 */
				int32		tuple_width = 0;
				int			i;

				for (i = 1; i <= RelationGetNumberOfAttributes(rel); i++)
				{
					Form_pg_attribute att = rel->rd_att->attrs[i - 1];
					int32		item_width;

					if (att->attisdropped)
						continue;
					/* This should match set_rel_width() in costsize.c */
					item_width = get_attavgwidth(RelationGetRelid(rel), i);
					if (item_width <= 0)
					{
						item_width = get_typavgwidth(att->atttypid,
													 att->atttypmod);
						Assert(item_width > 0);
					}
					if (attr_widths != NULL)
						attr_widths[i] = item_width;
					tuple_width += item_width;
				}
				tuple_width += sizeof(HeapTupleHeaderData);
				tuple_width += sizeof(ItemPointerData);
				/* note: integer division is intentional here */
				density = (BLCKSZ - sizeof(PageHeaderData)) / tuple_width;
			}
			*tuples = rint(density * (double) curpages);
			break;
		case RELKIND_SEQUENCE:
			/* Sequences always have a known size */
			*pages = 1;
			*tuples = 1;
			break;
		default:
			/* else it has no disk storage; probably shouldn't get here? */
			*pages = 0;
			*tuples = 0;
			break;
	}
}


/*
 * get_relation_constraints
 *
 * Retrieve the CHECK constraint expressions of the given relation.
 *
 * Returns a List (possibly empty) of constraint expressions.  Each one
 * has been canonicalized, and its Vars are changed to have the varno
 * indicated by rel->relid.  This allows the expressions to be easily
 * compared to expressions taken from WHERE.
 *
 * If include_notnull is true, "col IS NOT NULL" expressions are generated
 * and added to the result for each column that's marked attnotnull.
 *
 * Note: at present this is invoked at most once per relation per planner
 * run, and in many cases it won't be invoked at all, so there seems no
 * point in caching the data in RelOptInfo.
 */
static List *
get_relation_constraints(PlannerInfo *root,
						 Oid relationObjectId, RelOptInfo *rel,
						 bool include_notnull)
{
	List	   *result = NIL;
	Index		varno = rel->relid;
	Relation	relation;
	TupleConstr *constr;

	/*
	 * We assume the relation has already been safely locked.
	 */
	relation = heap_open(relationObjectId, NoLock);

	constr = relation->rd_att->constr;