exectuples.c

PostgreSQL7.4.6 for Linux

/*-------------------------------------------------------------------------
 *
 * execTuples.c
 *	  Routines dealing with the executor tuple tables.	These are used to
 *	  ensure that the executor frees copies of tuples (made by
 *	  ExecTargetList) properly.
 *
 *	  Routines dealing with the type information for tuples. Currently,
 *	  the type information for a tuple is an array of FormData_pg_attribute.
 *	  This information is needed by routines manipulating tuples
 *	  (getattribute, formtuple, etc.).
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/executor/execTuples.c,v 1.72 2003/09/29 18:22:48 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *
 *	 TABLE CREATE/DELETE
 *		ExecCreateTupleTable	- create a new tuple table
 *		ExecDropTupleTable		- destroy a table
 *
 *	 SLOT RESERVATION
 *		ExecAllocTableSlot		- find an available slot in the table
 *
 *	 SLOT ACCESSORS
 *		ExecStoreTuple			- store a tuple in the table
 *		ExecFetchTuple			- fetch a tuple from the table
 *		ExecClearTuple			- clear contents of a table slot
 *		ExecSetSlotDescriptor	- set a slot's tuple descriptor
 *		ExecSetSlotDescriptorIsNew - diddle the slot-desc-is-new flag
 *
 *	 SLOT STATUS PREDICATES
 *		TupIsNull				- true when slot contains no tuple(Macro)
 *
 *	 CONVENIENCE INITIALIZATION ROUTINES
 *		ExecInitResultTupleSlot    \	convenience routines to initialize
 *		ExecInitScanTupleSlot		\	the various tuple slots for nodes
 *		ExecInitExtraTupleSlot		/	which store copies of tuples.
 *		ExecInitNullTupleSlot	   /
 *
 *	 Routines that probably belong somewhere else:
 *		ExecTypeFromTL			- form a TupleDesc from a target list
 *
 *	 EXAMPLE OF HOW TABLE ROUTINES WORK
 *		Suppose we have a query such as retrieve (EMP.name) and we have
 *		a single SeqScan node in the query plan.
 *
 *		At ExecStart()
 *		----------------
 *		- InitPlan() calls ExecCreateTupleTable() to create the tuple
 *		  table which will hold tuples processed by the executor.
 *
 *		- ExecInitSeqScan() calls ExecInitScanTupleSlot() and
 *		  ExecInitResultTupleSlot() to reserve places in the tuple
 *		  table for the tuples returned by the access methods and the
 *		  tuples resulting from preforming target list projections.
 *
 *		During ExecRun()
 *		----------------
 *		- SeqNext() calls ExecStoreTuple() to place the tuple returned
 *		  by the access methods into the scan tuple slot.
 *
 *		- ExecSeqScan() calls ExecStoreTuple() to take the result
 *		  tuple from ExecProject() and place it into the result tuple slot.
 *
 *		- ExecutePlan() calls ExecRetrieve() which gets the tuple out of
 *		  the slot passed to it by calling ExecFetchTuple().  this tuple
 *		  is then returned.
 *
 *		At ExecEnd()
 *		----------------
 *		- EndPlan() calls ExecDropTupleTable() to clean up any remaining
 *		  tuples left over from executing the query.
 *
 *		The important thing to watch in the executor code is how pointers
 *		to the slots containing tuples are passed instead of the tuples
 *		themselves.  This facilitates the communication of related information
 *		(such as whether or not a tuple should be pfreed, what buffer contains
 *		this tuple, the tuple's tuple descriptor, etc).   Note that much of
 *		this information is also kept in the ExprContext of each node.
 *		Soon the executor will be redesigned and ExprContext's will contain
 *		only slot pointers.  -cim 3/14/91
 *
 *	 NOTES
 *		The tuple table stuff is relatively new, put here to alleviate
 *		the process growth problems in the executor.  The other routines
 *		are old (from the original lisp system) and may someday become
 *		obsolete.  -cim 6/23/90
 *
 *		In the implementation of nested-dot queries such as
 *		"retrieve (EMP.hobbies.all)", a single scan may return tuples
 *		of many types, so now we return pointers to tuple descriptors
 *		along with tuples returned via the tuple table.  This means
 *		we now have a bunch of routines to diddle the slot descriptors
 *		too.  -cim 1/18/90
 *
 *		The tuple table stuff depends on the executor/tuptable.h macros,
 *		and the TupleTableSlot node in execnodes.h.
 *
 */
#include "postgres.h"

#include "funcapi.h"
#include "access/heapam.h"
#include "executor/executor.h"
#include "utils/lsyscache.h"


/* ----------------------------------------------------------------
 *				  tuple table create/delete functions
 * ----------------------------------------------------------------
 */
/* --------------------------------
 *		ExecCreateTupleTable
 *
 *		This creates a new tuple table of the specified initial
 *		size.  If the size is insufficient, ExecAllocTableSlot()
 *		will grow the table as necessary.
 *
 *		This should be used by InitPlan() to allocate the table.
 *		The table's address will be stored in the EState structure.
 * --------------------------------
 */
TupleTable						/* return: address of table */
ExecCreateTupleTable(int initialSize)	/* initial number of slots in
										 * table */
{
	TupleTable	newtable;		/* newly allocated table */
	TupleTableSlot *array;		/* newly allocated slot array */

	/*
	 * sanity checks
	 */
	Assert(initialSize >= 1);

	/*
	 * Now allocate our new table along with space for the pointers to the
	 * tuples.
	 */

	newtable = (TupleTable) palloc(sizeof(TupleTableData));
	array = (TupleTableSlot *) palloc(initialSize * sizeof(TupleTableSlot));

	/*
	 * clean out the slots we just allocated
	 */
	MemSet(array, 0, initialSize * sizeof(TupleTableSlot));

	/*
	 * initialize the new table and return it to the caller.
	 */
	newtable->size = initialSize;
	newtable->next = 0;
	newtable->array = array;

	return newtable;
}

/* --------------------------------
 *		ExecDropTupleTable
 *
 *		This frees the storage used by the tuple table itself
 *		and optionally frees the contents of the table also.
 *		It is expected that this routine be called by EndPlan().
 * --------------------------------
 */
void
ExecDropTupleTable(TupleTable table,	/* tuple table */
				   bool shouldFree)		/* true if we should free slot
										 * contents */
{
	int			next;			/* next available slot */
	TupleTableSlot *array;		/* start of table array */
	int			i;				/* counter */

	/*
	 * sanity checks
	 */
	Assert(table != NULL);

	/*
	 * get information from the table
	 */
	array = table->array;
	next = table->next;

	/*
	 * first free all the valid pointers in the tuple array and drop
	 * refcounts of any referenced buffers, if that's what the caller
	 * wants.  (There is probably no good reason for the caller ever not
	 * to want it!)
	 */
	if (shouldFree)
	{
		for (i = 0; i < next; i++)
		{
			ExecClearTuple(&array[i]);
			if (array[i].ttc_shouldFreeDesc &&
				array[i].ttc_tupleDescriptor != NULL)
				FreeTupleDesc(array[i].ttc_tupleDescriptor);
		}
	}

	/*
	 * finally free the tuple array and the table itself.
	 */
	pfree(array);
	pfree(table);
}


/* ----------------------------------------------------------------
 *				  tuple table slot reservation functions
 * ----------------------------------------------------------------
 */
/* --------------------------------
 *		ExecAllocTableSlot
 *
 *		This routine is used to reserve slots in the table for
 *		use by the various plan nodes.	It is expected to be
 *		called by the node init routines (ex: ExecInitNestLoop)
 *		once per slot needed by the node.  Not all nodes need
 *		slots (some just pass tuples around).
 * --------------------------------
 */
TupleTableSlot *
ExecAllocTableSlot(TupleTable table)
{
	int			slotnum;		/* new slot number */
	TupleTableSlot *slot;

	/*
	 * sanity checks
	 */
	Assert(table != NULL);

	/*
	 * if our table is full we have to allocate a larger size table. Since
	 * ExecAllocTableSlot() is only called before the table is ever used
	 * to store tuples, we don't have to worry about the contents of the
	 * old table. If this changes, then we will have to preserve the
	 * contents. -cim 6/23/90
	 *
	 * Unfortunately, we *cannot* do this.	All of the nodes in the plan that
	 * have already initialized their slots will have pointers into
	 * _freed_ memory.	This leads to bad ends.  We now count the number
	 * of slots we will need and create all the slots we will need ahead
	 * of time.  The if below should never happen now.	Fail if it does.
	 * -mer 4 Aug 1992
	 */
	if (table->next >= table->size)
		elog(ERROR, "plan requires more slots than are available");

	/*
	 * at this point, space in the table is guaranteed so we reserve the
	 * next slot, initialize and return it.
	 */
	slotnum = table->next;
	table->next++;

	slot = &(table->array[slotnum]);

	/* Make sure the allocated slot is valid (and empty) */
	slot->type = T_TupleTableSlot;
	slot->val = (HeapTuple) NULL;
	slot->ttc_shouldFree = true;
	slot->ttc_descIsNew = true;
	slot->ttc_shouldFreeDesc = true;
	slot->ttc_tupleDescriptor = (TupleDesc) NULL;
	slot->ttc_buffer = InvalidBuffer;

	return slot;
}

/* --------------------------------
 *		MakeTupleTableSlot
 *
 *		This routine makes an empty standalone TupleTableSlot.
 *		It really shouldn't exist, but there are a few places
 *		that do this, so we may as well centralize the knowledge
 *		of what's in one ...
 * --------------------------------
 */
TupleTableSlot *
MakeTupleTableSlot(void)
{
	TupleTableSlot *slot = makeNode(TupleTableSlot);

	/* This should match ExecAllocTableSlot() */
	slot->val = (HeapTuple) NULL;
	slot->ttc_shouldFree = true;
	slot->ttc_descIsNew = true;
	slot->ttc_shouldFreeDesc = true;
	slot->ttc_tupleDescriptor = (TupleDesc) NULL;
	slot->ttc_buffer = InvalidBuffer;

	return slot;
}

/* ----------------------------------------------------------------
 *				  tuple table slot accessor functions
 * ----------------------------------------------------------------
 */

/* --------------------------------
 *		ExecStoreTuple
 *
 *		This function is used to store a tuple into a specified
 *		slot in the tuple table.
 *
 *		tuple:	tuple to store
 *		slot:	slot to store it in
 *		buffer: disk buffer if tuple is in a disk page, else InvalidBuffer
 *		shouldFree: true if ExecClearTuple should pfree() the tuple
 *					when done with it
 *
 * If 'buffer' is not InvalidBuffer, the tuple table code acquires a pin
 * on the buffer which is held until the slot is cleared, so that the tuple
 * won't go away on us.
 *
 * shouldFree is normally set 'true' for tuples constructed on-the-fly.
 * It must always be 'false' for tuples that are stored in disk pages,
 * since we don't want to try to pfree those.
 *
 * Another case where it is 'false' is when the referenced tuple is held
 * in a tuple table slot belonging to a lower-level executor Proc node.
 * In this case the lower-level slot retains ownership and responsibility
 * for eventually releasing the tuple.	When this method is used, we must
 * be certain that the upper-level Proc node will lose interest in the tuple
 * sooner than the lower-level one does!  If you're not certain, copy the
 * lower-level tuple with heap_copytuple and let the upper-level table
 * slot assume ownership of the copy!
 *
 * Return value is just the passed-in slot pointer.
 * --------------------------------
 */
TupleTableSlot *
ExecStoreTuple(HeapTuple tuple,
			   TupleTableSlot *slot,
			   Buffer buffer,
			   bool shouldFree)
{
	/*
	 * sanity checks
	 */
	Assert(slot != NULL);
	/* passing shouldFree=true for a tuple on a disk page is not sane */
	Assert(BufferIsValid(buffer) ? (!shouldFree) : true);

	/* clear out any old contents of the slot */
	ExecClearTuple(slot);

	/*
	 * store the new tuple into the specified slot and return the slot
	 * into which we stored the tuple.
	 */
	slot->val = tuple;
	slot->ttc_buffer = buffer;
	slot->ttc_shouldFree = shouldFree;

	/*
	 * If tuple is on a disk page, keep the page pinned as long as we hold
	 * a pointer into it.
	 */
	if (BufferIsValid(buffer))
		IncrBufferRefCount(buffer);

	return slot;
}

/* --------------------------------
 *		ExecClearTuple
 *
 *		This function is used to clear out a slot in the tuple table.
 *
 *		NB: only the tuple is cleared, not the tuple descriptor (if any).
 * --------------------------------
 */
TupleTableSlot *				/* return: slot passed */
ExecClearTuple(TupleTableSlot *slot)	/* slot in which to store tuple */
{
	HeapTuple	oldtuple;		/* prior contents of slot */

	/*
	 * sanity checks
	 */
	Assert(slot != NULL);

	/*
	 * get information from the tuple table
	 */
	oldtuple = slot->val;

	/*
	 * free the old contents of the specified slot if necessary.
	 */
	if (slot->ttc_shouldFree && oldtuple != NULL)
		heap_freetuple(oldtuple);

	slot->val = (HeapTuple) NULL;

	slot->ttc_shouldFree = true;	/* probably useless code... */

	/*
	 * Drop the pin on the referenced buffer, if there is one.
	 */
	if (BufferIsValid(slot->ttc_buffer))
		ReleaseBuffer(slot->ttc_buffer);

	slot->ttc_buffer = InvalidBuffer;

	return slot;
}