tuptable.h

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/*-------------------------------------------------------------------------
 *
 * tuptable.h
 *    tuple table support stuff
 *
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/executor/tuptable.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef TUPTABLE_H
#define TUPTABLE_H

#include "access/htup.h"
#include "access/htup_details.h"
#include "access/sysattr.h"
#include "access/tupdesc.h"
#include "storage/buf.h"

/*----------
 * The executor stores tuples in a "tuple table" which is a List of
 * independent TupleTableSlots.
 *
 * There's various different types of tuple table slots, each being able to
 * store different types of tuples. Additional types of slots can be added
 * without modifying core code. The type of a slot is determined by the
 * TupleTableSlotOps* passed to the slot creation routine. The builtin types
 * of slots are
 *
 * 1. physical tuple in a disk buffer page (TTSOpsBufferHeapTuple)
 * 2. physical tuple constructed in palloc'ed memory (TTSOpsHeapTuple)
 * 3. "minimal" physical tuple constructed in palloc'ed memory
 *    (TTSOpsMinimalTuple)
 * 4. "virtual" tuple consisting of Datum/isnull arrays (TTSOpsVirtual)
 *
 *
 * The first two cases are similar in that they both deal with "materialized"
 * tuples, but resource management is different.  For a tuple in a disk page
 * we need to hold a pin on the buffer until the TupleTableSlot's reference
 * to the tuple is dropped; while for a palloc'd tuple we usually want the
 * tuple pfree'd when the TupleTableSlot's reference is dropped.
 *
 * A "minimal" tuple is handled similarly to a palloc'd regular tuple.
 * At present, minimal tuples never are stored in buffers, so there is no
 * parallel to case 1.  Note that a minimal tuple has no "system columns".
 * (Actually, it could have an OID, but we have no need to access the OID.)
 *
 * A "virtual" tuple is an optimization used to minimize physical data copying
 * in a nest of plan nodes.  Until materialized pass-by-reference Datums in
 * the slot point to storage that is not directly associated with the
 * TupleTableSlot; generally they will point to part of a tuple stored in a
 * lower plan node's output TupleTableSlot, or to a function result
 * constructed in a plan node's per-tuple econtext.  It is the responsibility
 * of the generating plan node to be sure these resources are not released for
 * as long as the virtual tuple needs to be valid or is materialized.  Note
 * also that a virtual tuple does not have any "system columns".
 *
 * The Datum/isnull arrays of a TupleTableSlot serve double duty.  For virtual
 * slots they are the authoritative data.  For the other builtin slots,
 * the arrays contain data extracted from the tuple.  (In this state, any
 * pass-by-reference Datums point into the physical tuple.)  The extracted
 * information is built "lazily", ie, only as needed.  This serves to avoid
 * repeated extraction of data from the physical tuple.
 *
 * A TupleTableSlot can also be "empty", indicated by flag TTS_FLAG_EMPTY set
 * in tts_flags, holding no valid data.  This is the only valid state for a
 * freshly-created slot that has not yet had a tuple descriptor assigned to
 * it.  In this state, TTS_SHOULDFREE should not be set in tts_flags, tts_tuple
 * must be NULL and tts_nvalid zero.
 *
 * The tupleDescriptor is simply referenced, not copied, by the TupleTableSlot
 * code.  The caller of ExecSetSlotDescriptor() is responsible for providing
 * a descriptor that will live as long as the slot does.  (Typically, both
 * slots and descriptors are in per-query memory and are freed by memory
 * context deallocation at query end; so it's not worth providing any extra
 * mechanism to do more.  However, the slot will increment the tupdesc
 * reference count if a reference-counted tupdesc is supplied.)
 *
 * When TTS_SHOULDFREE is set in tts_flags, the physical tuple is "owned" by
 * the slot and should be freed when the slot's reference to the tuple is
 * dropped.
 *
 * tts_values/tts_isnull are allocated either when the slot is created (when
 * the descriptor is provided), or when a descriptor is assigned to the slot;
 * they are of length equal to the descriptor's natts.
 *
 * The TTS_FLAG_SLOW flag is saved state for
 * slot_deform_heap_tuple, and should not be touched by any other code.
 *----------
 */

/* true = slot is empty */
#define         TTS_FLAG_EMPTY          (1 << 1)
#define TTS_EMPTY(slot) (((slot)->tts_flags & TTS_FLAG_EMPTY) != 0)

/* should pfree tuple "owned" by the slot? */
#define         TTS_FLAG_SHOULDFREE     (1 << 2)
#define TTS_SHOULDFREE(slot) (((slot)->tts_flags & TTS_FLAG_SHOULDFREE) != 0)

/* saved state for slot_deform_heap_tuple */
#define         TTS_FLAG_SLOW       (1 << 3)
#define TTS_SLOW(slot) (((slot)->tts_flags & TTS_FLAG_SLOW) != 0)

/* fixed tuple descriptor */
#define         TTS_FLAG_FIXED      (1 << 4)
#define TTS_FIXED(slot) (((slot)->tts_flags & TTS_FLAG_FIXED) != 0)

struct TupleTableSlotOps;
typedef struct TupleTableSlotOps TupleTableSlotOps;

/* base tuple table slot type */
typedef struct TupleTableSlot
{
    NodeTag     type;
#define FIELDNO_TUPLETABLESLOT_FLAGS 1
    uint16      tts_flags;      /* Boolean states */
#define FIELDNO_TUPLETABLESLOT_NVALID 2
    AttrNumber  tts_nvalid;     /* # of valid values in tts_values */
    const TupleTableSlotOps *const tts_ops; /* implementation of slot */
#define FIELDNO_TUPLETABLESLOT_TUPLEDESCRIPTOR 4
    TupleDesc   tts_tupleDescriptor;    /* slot's tuple descriptor */
#define FIELDNO_TUPLETABLESLOT_VALUES 5
    Datum      *tts_values;     /* current per-attribute values */
#define FIELDNO_TUPLETABLESLOT_ISNULL 6
    bool       *tts_isnull;     /* current per-attribute isnull flags */
    MemoryContext tts_mcxt;     /* slot itself is in this context */
    ItemPointerData tts_tid;    /* stored tuple's tid */
    Oid         tts_tableOid;   /* table oid of tuple */
} TupleTableSlot;

/* routines for a TupleTableSlot implementation */
struct TupleTableSlotOps
{
    /* Minimum size of the slot */
    size_t      base_slot_size;

    /* Initialization. */
    void        (*init) (TupleTableSlot *slot);

    /* Destruction. */
    void        (*release) (TupleTableSlot *slot);

    /*
     * Clear the contents of the slot. Only the contents are expected to be
     * cleared and not the tuple descriptor. Typically an implementation of
     * this callback should free the memory allocated for the tuple contained
     * in the slot.
     */
    void        (*clear) (TupleTableSlot *slot);

    /*
     * Fill up first natts entries of tts_values and tts_isnull arrays with
     * values from the tuple contained in the slot. The function may be called
     * with natts more than the number of attributes available in the tuple,
     * in which case it should set tts_nvalid to the number of returned
     * columns.
     */
    void        (*getsomeattrs) (TupleTableSlot *slot, int natts);

    /*
     * Returns value of the given system attribute as a datum and sets isnull
     * to false, if it's not NULL. Throws an error if the slot type does not
     * support system attributes.
     */
    Datum       (*getsysattr) (TupleTableSlot *slot, int attnum, bool *isnull);

    /*
     * Make the contents of the slot solely depend on the slot, and not on
     * underlying resources (like another memory context, buffers, etc).
     */
    void        (*materialize) (TupleTableSlot *slot);

    /*
     * Copy the contents of the source slot into the destination slot's own
     * context. Invoked using callback of the destination slot.
     */
    void        (*copyslot) (TupleTableSlot *dstslot, TupleTableSlot *srcslot);

    /*
     * Return a heap tuple "owned" by the slot. It is slot's responsibility to
     * free the memory consumed by the heap tuple. If the slot can not "own" a
     * heap tuple, it should not implement this callback and should set it as
     * NULL.
     */
    HeapTuple   (*get_heap_tuple) (TupleTableSlot *slot);

    /*
     * Return a minimal tuple "owned" by the slot. It is slot's responsibility
     * to free the memory consumed by the minimal tuple. If the slot can not
     * "own" a minimal tuple, it should not implement this callback and should
     * set it as NULL.
     */
    MinimalTuple (*get_minimal_tuple) (TupleTableSlot *slot);

    /*
     * Return a copy of heap tuple representing the contents of the slot. The
     * copy needs to be palloc'd in the current memory context. The slot
     * itself is expected to remain unaffected. It is *not* expected to have
     * meaningful "system columns" in the copy. The copy is not be "owned" by
     * the slot i.e. the caller has to take responsibility to free memory
     * consumed by the slot.
     */
    HeapTuple   (*copy_heap_tuple) (TupleTableSlot *slot);

    /*
     * Return a copy of minimal tuple representing the contents of the slot.
     * The copy needs to be palloc'd in the current memory context. The slot
     * itself is expected to remain unaffected. It is *not* expected to have
     * meaningful "system columns" in the copy. The copy is not be "owned" by
     * the slot i.e. the caller has to take responsibility to free memory
     * consumed by the slot.
     */
    MinimalTuple (*copy_minimal_tuple) (TupleTableSlot *slot);
};

/*
 * Predefined TupleTableSlotOps for various types of TupleTableSlotOps. The
 * same are used to identify the type of a given slot.
 */
extern PGDLLIMPORT const TupleTableSlotOps TTSOpsVirtual;
extern PGDLLIMPORT const TupleTableSlotOps TTSOpsHeapTuple;
extern PGDLLIMPORT const TupleTableSlotOps TTSOpsMinimalTuple;
extern PGDLLIMPORT const TupleTableSlotOps TTSOpsBufferHeapTuple;

#define TTS_IS_VIRTUAL(slot) ((slot)->tts_ops == &TTSOpsVirtual)
#define TTS_IS_HEAPTUPLE(slot) ((slot)->tts_ops == &TTSOpsHeapTuple)
#define TTS_IS_MINIMALTUPLE(slot) ((slot)->tts_ops == &TTSOpsMinimalTuple)
#define TTS_IS_BUFFERTUPLE(slot) ((slot)->tts_ops == &TTSOpsBufferHeapTuple)


/*
 * Tuple table slot implementations.
 */

typedef struct VirtualTupleTableSlot
{
    TupleTableSlot base;

    char       *data;           /* data for materialized slots */
} VirtualTupleTableSlot;

typedef struct HeapTupleTableSlot
{
    TupleTableSlot base;

#define FIELDNO_HEAPTUPLETABLESLOT_TUPLE 1
    HeapTuple   tuple;          /* physical tuple */
#define FIELDNO_HEAPTUPLETABLESLOT_OFF 2
    uint32      off;            /* saved state for slot_deform_heap_tuple */
    HeapTupleData tupdata;      /* optional workspace for storing tuple */
} HeapTupleTableSlot;

/* heap tuple residing in a buffer */
typedef struct BufferHeapTupleTableSlot
{
    HeapTupleTableSlot base;

    /*
     * If buffer is not InvalidBuffer, then the slot is holding a pin on the
     * indicated buffer page; drop the pin when we release the slot's
     * reference to that buffer.  (TTS_FLAG_SHOULDFREE should not be set in
     * such a case, since presumably tts_tuple is pointing into the buffer.)
     */
    Buffer      buffer;         /* tuple's buffer, or InvalidBuffer */
} BufferHeapTupleTableSlot;

typedef struct MinimalTupleTableSlot
{
    TupleTableSlot base;

    /*
     * In a minimal slot tuple points at minhdr and the fields of that struct
     * are set correctly for access to the minimal tuple; in particular,
     * minhdr.t_data points MINIMAL_TUPLE_OFFSET bytes before mintuple.  This
     * allows column extraction to treat the case identically to regular
     * physical tuples.
     */
#define FIELDNO_MINIMALTUPLETABLESLOT_TUPLE 1
    HeapTuple   tuple;          /* tuple wrapper */
    MinimalTuple mintuple;      /* minimal tuple, or NULL if none */
    HeapTupleData minhdr;       /* workspace for minimal-tuple-only case */
#define FIELDNO_MINIMALTUPLETABLESLOT_OFF 4
    uint32      off;            /* saved state for slot_deform_heap_tuple */
} MinimalTupleTableSlot;

/*
 * TupIsNull -- is a TupleTableSlot empty?
 */
#define TupIsNull(slot) \
    ((slot) == NULL || TTS_EMPTY(slot))

/* in executor/execTuples.c */
extern TupleTableSlot *MakeTupleTableSlot(TupleDesc tupleDesc,
                                          const TupleTableSlotOps *tts_ops);
extern TupleTableSlot *ExecAllocTableSlot(List **tupleTable, TupleDesc desc,
                                          const TupleTableSlotOps *tts_ops);
extern void ExecResetTupleTable(List *tupleTable, bool shouldFree);
extern TupleTableSlot *MakeSingleTupleTableSlot(TupleDesc tupdesc,
                                                const TupleTableSlotOps *tts_ops);
extern void ExecDropSingleTupleTableSlot(TupleTableSlot *slot);
extern void ExecSetSlotDescriptor(TupleTableSlot *slot, TupleDesc tupdesc);
extern TupleTableSlot *ExecStoreHeapTuple(HeapTuple tuple,
                                          TupleTableSlot *slot,
                                          bool shouldFree);
extern void ExecForceStoreHeapTuple(HeapTuple tuple,
                                    TupleTableSlot *slot,
                                    bool shouldFree);
extern TupleTableSlot *ExecStoreBufferHeapTuple(HeapTuple tuple,
                                                TupleTableSlot *slot,
                                                Buffer buffer);
extern TupleTableSlot *ExecStorePinnedBufferHeapTuple(HeapTuple tuple,
                                                      TupleTableSlot *slot,
                                                      Buffer buffer);
extern TupleTableSlot *ExecStoreMinimalTuple(MinimalTuple mtup,
                                             TupleTableSlot *slot,
                                             bool shouldFree);
extern void ExecForceStoreMinimalTuple(MinimalTuple mtup, TupleTableSlot *slot,
                                       bool shouldFree);
extern TupleTableSlot *ExecStoreVirtualTuple(TupleTableSlot *slot);
extern TupleTableSlot *ExecStoreAllNullTuple(TupleTableSlot *slot);
extern void ExecStoreHeapTupleDatum(Datum data, TupleTableSlot *slot);
extern HeapTuple ExecFetchSlotHeapTuple(TupleTableSlot *slot, bool materialize, bool *shouldFree);
extern MinimalTuple ExecFetchSlotMinimalTuple(TupleTableSlot *slot,
                                              bool *shouldFree);
extern Datum ExecFetchSlotHeapTupleDatum(TupleTableSlot *slot);
extern void slot_getmissingattrs(TupleTableSlot *slot, int startAttNum,
                                 int lastAttNum);
extern void slot_getsomeattrs_int(TupleTableSlot *slot, int attnum);


#ifndef FRONTEND

/*
 * This function forces the entries of the slot's Datum/isnull arrays to be
 * valid at least up through the attnum'th entry.
 */
static inline void
slot_getsomeattrs(TupleTableSlot *slot, int attnum)
{
    if (slot->tts_nvalid < attnum)
        slot_getsomeattrs_int(slot, attnum);
}

/*
 * slot_getallattrs
 *      This function forces all the entries of the slot's Datum/isnull
 *      arrays to be valid.  The caller may then extract data directly
 *      from those arrays instead of using slot_getattr.
 */
static inline void
slot_getallattrs(TupleTableSlot *slot)
{
    slot_getsomeattrs(slot, slot->tts_tupleDescriptor->natts);
}


/*
 * slot_attisnull
 *
 * Detect whether an attribute of the slot is null, without actually fetching
 * it.
 */
static inline bool
slot_attisnull(TupleTableSlot *slot, int attnum)
{
    AssertArg(attnum > 0);

    if (attnum > slot->tts_nvalid)
        slot_getsomeattrs(slot, attnum);

    return slot->tts_isnull[attnum - 1];
}

/*
 * slot_getattr - fetch one attribute of the slot's contents.
 */
static inline Datum
slot_getattr(TupleTableSlot *slot, int attnum,
             bool *isnull)
{
    AssertArg(attnum > 0);

    if (attnum > slot->tts_nvalid)
        slot_getsomeattrs(slot, attnum);

    *isnull = slot->tts_isnull[attnum - 1];

    return slot->tts_values[attnum - 1];
}

/*
 * slot_getsysattr - fetch a system attribute of the slot's current tuple.
 *
 *  If the slot type does not contain system attributes, this will throw an
 *  error.  Hence before calling this function, callers should make sure that
 *  the slot type is the one that supports system attributes.
 */
static inline Datum
slot_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
{
    AssertArg(attnum < 0);      /* caller error */

    if (attnum == TableOidAttributeNumber)
    {
        *isnull = false;
        return ObjectIdGetDatum(slot->tts_tableOid);
    }
    else if (attnum == SelfItemPointerAttributeNumber)
    {
        *isnull = false;
        return PointerGetDatum(&slot->tts_tid);
    }

    /* Fetch the system attribute from the underlying tuple. */
    return slot->tts_ops->getsysattr(slot, attnum, isnull);
}

/*
 * ExecClearTuple - clear the slot's contents
 */
static inline TupleTableSlot *
ExecClearTuple(TupleTableSlot *slot)
{
    slot->tts_ops->clear(slot);

    return slot;
}

/* ExecMaterializeSlot - force a slot into the "materialized" state.
 *
 * This causes the slot's tuple to be a local copy not dependent on any
 * external storage (i.e. pointing into a Buffer, or having allocations in
 * another memory context).
 *
 * A typical use for this operation is to prepare a computed tuple for being
 * stored on disk.  The original data may or may not be virtual, but in any
 * case we need a private copy for heap_insert to scribble on.
 */
static inline void
ExecMaterializeSlot(TupleTableSlot *slot)
{
    slot->tts_ops->materialize(slot);
}

/*
 * ExecCopySlotHeapTuple - return HeapTuple allocated in caller's context
 */
static inline HeapTuple
ExecCopySlotHeapTuple(TupleTableSlot *slot)
{
    Assert(!TTS_EMPTY(slot));

    return slot->tts_ops->copy_heap_tuple(slot);
}

/*
 * ExecCopySlotMinimalTuple - return MinimalTuple allocated in caller's context
 */
static inline MinimalTuple
ExecCopySlotMinimalTuple(TupleTableSlot *slot)
{
    return slot->tts_ops->copy_minimal_tuple(slot);
}

/*
 * ExecCopySlot - copy one slot's contents into another.
 *
 * If a source's system attributes are supposed to be accessed in the target
 * slot, the target slot and source slot types need to match.
 */
static inline TupleTableSlot *
ExecCopySlot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
{
    Assert(!TTS_EMPTY(srcslot));
    AssertArg(srcslot != dstslot);

    dstslot->tts_ops->copyslot(dstslot, srcslot);

    return dstslot;
}

#endif                          /* FRONTEND */

#endif                          /* TUPTABLE_H */