/*-------------------------------------------------------------------------
 *
 * nodeBitmapIndexscan.c
 *	  Routines to support bitmapped index scans of relations
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/executor/nodeBitmapIndexscan.c,v 1.6 2005/04/24 18:16:38 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *		MultiExecBitmapIndexScan	scans a relation using index.
 *		ExecInitBitmapIndexScan		creates and initializes state info.
 *		ExecBitmapIndexReScan		prepares to rescan the plan.
 *		ExecEndBitmapIndexScan		releases all storage.
 */
#include "postgres.h"

#include "access/genam.h"
#include "access/heapam.h"
#include "executor/execdebug.h"
#include "executor/instrument.h"
#include "executor/nodeBitmapIndexscan.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "parser/parsetree.h"


/* ----------------------------------------------------------------
 *		MultiExecBitmapIndexScan(node)
 * ----------------------------------------------------------------
 */
Node *
MultiExecBitmapIndexScan(BitmapIndexScanState *node)
{
#define MAX_TIDS	1024
	TIDBitmap  *tbm;
	Oid			indxid;
	Relation	indexRelation;
	IndexScanDesc scandesc;
	ItemPointerData tids[MAX_TIDS];
	int32		ntids;
	double		nTuples = 0;

	/* must provide our own instrumentation support */
	if (node->ss.ps.instrument)
		InstrStartNode(node->ss.ps.instrument);

	/*
	 * If we have runtime keys and they've not already been set up, do it
	 * now.
	 */
	if (node->biss_RuntimeKeyInfo && !node->biss_RuntimeKeysReady)
		ExecReScan((PlanState *) node, NULL);

	/*
	 * We do not open or lock the base relation here.  We assume that an
	 * ancestor BitmapHeapScan node is holding AccessShareLock on the
	 * heap relation throughout the execution of the plan tree.
	 */

	/*
	 * open the index relation and initialize relation and scan
	 * descriptors.  Note we acquire no locks here; the index machinery
	 * does its own locks and unlocks.
	 */
	indxid = ((BitmapIndexScan *) node->ss.ps.plan)->indxid;
	indexRelation = index_open(indxid);
	scandesc = index_beginscan_multi(indexRelation,
									 node->ss.ps.state->es_snapshot,
									 node->biss_NumScanKeys,
									 node->biss_ScanKeys);

	/*
	 * Prepare the result bitmap.  Normally we just create a new one to pass
	 * back; however, our parent node is allowed to store a pre-made one
	 * into node->biss_result, in which case we just OR our tuple IDs into
	 * the existing bitmap.  (This saves needing explicit UNION steps.)
	 */
	if (node->biss_result)
	{
		tbm = node->biss_result;
		node->biss_result = NULL;		/* reset for next time */
	}
	else
	{
		/* XXX should we use less than work_mem for this? */
		tbm = tbm_create(work_mem * 1024L);
	}

	/*
	 * Get TIDs from index and insert into bitmap
	 */
	for (;;)
	{
		bool	more = index_getmulti(scandesc, tids, MAX_TIDS, &ntids);

		if (ntids > 0)
		{
			tbm_add_tuples(tbm, tids, ntids);
			nTuples += ntids;
		}

		if (!more)
			break;

		CHECK_FOR_INTERRUPTS();
	}

	/*
	 * close the index relation
	 */
	index_endscan(scandesc);
	index_close(indexRelation);

	/* must provide our own instrumentation support */
	if (node->ss.ps.instrument)
		InstrStopNodeMulti(node->ss.ps.instrument, nTuples);

	return (Node *) tbm;
}

/* ----------------------------------------------------------------
 *		ExecBitmapIndexReScan(node)
 *
 *		Recalculates the value of the scan keys whose value depends on
 *		information known at runtime.
 * ----------------------------------------------------------------
 */
void
ExecBitmapIndexReScan(BitmapIndexScanState *node, ExprContext *exprCtxt)
{
	ExprContext *econtext;
	ExprState **runtimeKeyInfo;

	econtext = node->biss_RuntimeContext;		/* context for runtime
												 * keys */
	runtimeKeyInfo = node->biss_RuntimeKeyInfo;

	if (econtext)
	{
		/*
		 * If we are being passed an outer tuple, save it for runtime key
		 * calc.
		 */
		if (exprCtxt != NULL)
			econtext->ecxt_outertuple = exprCtxt->ecxt_outertuple;

		/*
		 * Reset the runtime-key context so we don't leak memory as each
		 * outer tuple is scanned.	Note this assumes that we will
		 * recalculate *all* runtime keys on each call.
		 */
		ResetExprContext(econtext);
	}

	/*
	 * If we are doing runtime key calculations (ie, the index keys depend
	 * on data from an outer scan), compute the new key values
	 */
	if (runtimeKeyInfo)
	{
		int			n_keys;
		ScanKey		scan_keys;
		ExprState **run_keys;
		int			j;

		n_keys = node->biss_NumScanKeys;
		scan_keys = node->biss_ScanKeys;
		run_keys = runtimeKeyInfo;

		for (j = 0; j < n_keys; j++)
		{
			/*
			 * If we have a run-time key, then extract the run-time
			 * expression and evaluate it with respect to the current
			 * outer tuple.  We then stick the result into the scan
			 * key.
			 *
			 * Note: the result of the eval could be a pass-by-ref value
			 * that's stored in the outer scan's tuple, not in
			 * econtext->ecxt_per_tuple_memory.  We assume that the
			 * outer tuple will stay put throughout our scan.  If this
			 * is wrong, we could copy the result into our context
			 * explicitly, but I think that's not necessary...
			 */
			if (run_keys[j] != NULL)
			{
				Datum		scanvalue;
				bool		isNull;

				scanvalue = ExecEvalExprSwitchContext(run_keys[j],
													  econtext,
													  &isNull,
													  NULL);
				scan_keys[j].sk_argument = scanvalue;
				if (isNull)
					scan_keys[j].sk_flags |= SK_ISNULL;
				else
					scan_keys[j].sk_flags &= ~SK_ISNULL;
			}
		}

		node->biss_RuntimeKeysReady = true;
	}
}

/* ----------------------------------------------------------------
 *		ExecEndBitmapIndexScan
 * ----------------------------------------------------------------
 */
void
ExecEndBitmapIndexScan(BitmapIndexScanState *node)
{
	/*
	 * Free the exprcontext ... now dead code, see ExecFreeExprContext
	 */
#ifdef NOT_USED
	if (node->biss_RuntimeContext)
		FreeExprContext(node->biss_RuntimeContext);
#endif
}

/* ----------------------------------------------------------------
 *		ExecInitBitmapIndexScan
 *
 *		Initializes the index scan's state information.
 * ----------------------------------------------------------------
 */
BitmapIndexScanState *
ExecInitBitmapIndexScan(BitmapIndexScan *node, EState *estate)
{
	BitmapIndexScanState *indexstate;
	ExprState **runtimeKeyInfo;
	bool		have_runtime_keys;

	/*
	 * create state structure
	 */
	indexstate = makeNode(BitmapIndexScanState);
	indexstate->ss.ps.plan = (Plan *) node;
	indexstate->ss.ps.state = estate;

	/* normally we don't make the result bitmap till runtime */
	indexstate->biss_result = NULL;

	/*
	 * Miscellaneous initialization
	 *
	 * We do not need a standard exprcontext for this node, though we may
	 * decide below to create a runtime-key exprcontext
	 */

	/*
	 * initialize child expressions
	 *
	 * We don't need to initialize targetlist or qual since neither are used.
	 *
	 * Note: we don't initialize all of the indxqual expression, only the
	 * sub-parts corresponding to runtime keys (see below).
	 */

#define BITMAPINDEXSCAN_NSLOTS 0

	/*
	 * Initialize index-specific scan state
	 */
	indexstate->biss_ScanKeys = NULL;
	indexstate->biss_NumScanKeys = 0;
	indexstate->biss_RuntimeKeyInfo = NULL;
	indexstate->biss_RuntimeContext = NULL;
	indexstate->biss_RuntimeKeysReady = false;

	CXT1_printf("ExecInitBitmapIndexScan: context is %d\n", CurrentMemoryContext);

	/*
	 * initialize space for runtime key info (may not be needed)
	 */
	have_runtime_keys = false;

	/*
	 * build the index scan keys from the index qualification
	 */
	{
		List	   *quals;
		List	   *strategies;
		List	   *subtypes;
		ListCell   *qual_cell;
		ListCell   *strategy_cell;
		ListCell   *subtype_cell;
		int			n_keys;
		ScanKey		scan_keys;
		ExprState **run_keys;
		int			j;

		quals = node->indxqual;
		strategies = node->indxstrategy;
		subtypes = node->indxsubtype;
		n_keys = list_length(quals);
		scan_keys = (n_keys <= 0) ? NULL :
			(ScanKey) palloc(n_keys * sizeof(ScanKeyData));
		run_keys = (n_keys <= 0) ? NULL :
			(ExprState **) palloc(n_keys * sizeof(ExprState *));

		/*
		 * for each opclause in the given qual, convert each qual's
		 * opclause into a single scan key
		 */
		qual_cell = list_head(quals);
		strategy_cell = list_head(strategies);
		subtype_cell = list_head(subtypes);
		for (j = 0; j < n_keys; j++)
		{
			OpExpr	   *clause; /* one clause of index qual */
			Expr	   *leftop; /* expr on lhs of operator */
			Expr	   *rightop;	/* expr on rhs ... */
			int			flags = 0;
			AttrNumber	varattno;		/* att number used in scan */
			StrategyNumber strategy;	/* op's strategy number */
			Oid			subtype;	/* op's strategy subtype */
			RegProcedure opfuncid;		/* operator proc id used in scan */
			Datum		scanvalue;		/* value used in scan (if const) */

			/*
			 * extract clause information from the qualification
			 */
			clause = (OpExpr *) lfirst(qual_cell);
			qual_cell = lnext(qual_cell);
			strategy = lfirst_int(strategy_cell);
			strategy_cell = lnext(strategy_cell);
			subtype = lfirst_oid(subtype_cell);
			subtype_cell = lnext(subtype_cell);

			if (!IsA(clause, OpExpr))
				elog(ERROR, "indxqual is not an OpExpr");

			opfuncid = clause->opfuncid;

			/*
			 * Here we figure out the contents of the index qual. The
			 * usual case is (var op const) which means we form a scan key
			 * for the attribute listed in the var node and use the value
			 * of the const as comparison data.
			 *
			 * If we don't have a const node, it means our scan key is a
			 * function of information obtained during the execution of
			 * the plan, in which case we need to recalculate the index
			 * scan key at run time.  Hence, we set have_runtime_keys to
			 * true and place the appropriate subexpression in run_keys.
			 * The corresponding scan key values are recomputed at run
			 * time.
			 */
			run_keys[j] = NULL;

			/*
			 * determine information in leftop
			 */
			leftop = (Expr *) get_leftop((Expr *) clause);

			if (leftop && IsA(leftop, RelabelType))
				leftop = ((RelabelType *) leftop)->arg;

			Assert(leftop != NULL);

			if (!(IsA(leftop, Var) &&
				  var_is_rel((Var *) leftop)))
				elog(ERROR, "indxqual doesn't have key on left side");

			varattno = ((Var *) leftop)->varattno;

			/*
			 * now determine information in rightop
			 */
			rightop = (Expr *) get_rightop((Expr *) clause);

			if (rightop && IsA(rightop, RelabelType))
				rightop = ((RelabelType *) rightop)->arg;

			Assert(rightop != NULL);

			if (IsA(rightop, Const))
			{
				/*
				 * if the rightop is a const node then it means it
				 * identifies the value to place in our scan key.
				 */
				scanvalue = ((Const *) rightop)->constvalue;
				if (((Const *) rightop)->constisnull)
					flags |= SK_ISNULL;
			}
			else
			{
				/*
				 * otherwise, the rightop contains an expression evaluable
				 * at runtime to figure out the value to place in our scan
				 * key.
				 */
				have_runtime_keys = true;
				run_keys[j] = ExecInitExpr(rightop, (PlanState *) indexstate);
				scanvalue = (Datum) 0;
			}

			/*
			 * initialize the scan key's fields appropriately
			 */
			ScanKeyEntryInitialize(&scan_keys[j],
								   flags,
								   varattno,	/* attribute number to
												 * scan */
								   strategy,	/* op's strategy */
								   subtype,		/* strategy subtype */
								   opfuncid,	/* reg proc to use */
								   scanvalue);	/* constant */
		}

		/*
		 * store the key information into the node.
		 */
		indexstate->biss_NumScanKeys = n_keys;
		indexstate->biss_ScanKeys = scan_keys;
		runtimeKeyInfo = run_keys;
	}

	/*
	 * If all of our keys have the form (var op const), then we have no
	 * runtime keys so we store NULL in the runtime key info. Otherwise
	 * runtime key info contains an array of pointers to runtime key
	 * expressions.
	 *
	 * If we do have runtime keys, we need an ExprContext to evaluate them.
	 * We could just create a "standard" plan node exprcontext, but to
	 * keep the code looking similar to nodeIndexscan.c, it seems better
	 * to stick with the approach of using a separate ExprContext.
	 */
	if (have_runtime_keys)
	{
		ExprContext *stdecontext = indexstate->ss.ps.ps_ExprContext;

		ExecAssignExprContext(estate, &indexstate->ss.ps);
		indexstate->biss_RuntimeKeyInfo = runtimeKeyInfo;
		indexstate->biss_RuntimeContext = indexstate->ss.ps.ps_ExprContext;
		indexstate->ss.ps.ps_ExprContext = stdecontext;
	}
	else
	{
		indexstate->biss_RuntimeKeyInfo = NULL;
		indexstate->biss_RuntimeContext = NULL;
		/* Get rid of the speculatively-allocated flag array, too */
		if (runtimeKeyInfo)
			pfree(runtimeKeyInfo);
	}

	/* We don't keep the table or index open across calls */
	indexstate->ss.ss_currentRelation = NULL;
	indexstate->ss.ss_currentScanDesc = NULL;

	/*
	 * all done.
	 */
	return indexstate;
}

int
ExecCountSlotsBitmapIndexScan(BitmapIndexScan *node)
{
	return ExecCountSlotsNode(outerPlan((Plan *) node)) +
		ExecCountSlotsNode(innerPlan((Plan *) node)) + BITMAPINDEXSCAN_NSLOTS;
}