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173 lines
8.4 KiB
C
173 lines
8.4 KiB
C
/*-------------------------------------------------------------------------
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*
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* tuptable.h
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* tuple table support stuff
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*
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*
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* Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/executor/tuptable.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef TUPTABLE_H
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#define TUPTABLE_H
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#include "access/htup.h"
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#include "access/tupdesc.h"
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#include "storage/buf.h"
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/*----------
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* The executor stores tuples in a "tuple table" which is a List of
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* independent TupleTableSlots. There are several cases we need to handle:
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* 1. physical tuple in a disk buffer page
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* 2. physical tuple constructed in palloc'ed memory
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* 3. "minimal" physical tuple constructed in palloc'ed memory
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* 4. "virtual" tuple consisting of Datum/isnull arrays
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*
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* The first two cases are similar in that they both deal with "materialized"
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* tuples, but resource management is different. For a tuple in a disk page
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* we need to hold a pin on the buffer until the TupleTableSlot's reference
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* to the tuple is dropped; while for a palloc'd tuple we usually want the
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* tuple pfree'd when the TupleTableSlot's reference is dropped.
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*
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* A "minimal" tuple is handled similarly to a palloc'd regular tuple.
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* At present, minimal tuples never are stored in buffers, so there is no
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* parallel to case 1. Note that a minimal tuple has no "system columns".
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* (Actually, it could have an OID, but we have no need to access the OID.)
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*
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* A "virtual" tuple is an optimization used to minimize physical data
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* copying in a nest of plan nodes. Any pass-by-reference Datums in the
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* tuple point to storage that is not directly associated with the
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* TupleTableSlot; generally they will point to part of a tuple stored in
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* a lower plan node's output TupleTableSlot, or to a function result
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* constructed in a plan node's per-tuple econtext. It is the responsibility
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* of the generating plan node to be sure these resources are not released
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* for as long as the virtual tuple needs to be valid. We only use virtual
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* tuples in the result slots of plan nodes --- tuples to be copied anywhere
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* else need to be "materialized" into physical tuples. Note also that a
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* virtual tuple does not have any "system columns".
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*
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* It is also possible for a TupleTableSlot to hold both physical and minimal
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* copies of a tuple. This is done when the slot is requested to provide
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* the format other than the one it currently holds. (Originally we attempted
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* to handle such requests by replacing one format with the other, but that
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* had the fatal defect of invalidating any pass-by-reference Datums pointing
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* into the existing slot contents.) Both copies must contain identical data
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* payloads when this is the case.
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*
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* The Datum/isnull arrays of a TupleTableSlot serve double duty. When the
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* slot contains a virtual tuple, they are the authoritative data. When the
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* slot contains a physical tuple, the arrays contain data extracted from
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* the tuple. (In this state, any pass-by-reference Datums point into
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* the physical tuple.) The extracted information is built "lazily",
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* ie, only as needed. This serves to avoid repeated extraction of data
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* from the physical tuple.
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*
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* A TupleTableSlot can also be "empty", holding no valid data. This is
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* the only valid state for a freshly-created slot that has not yet had a
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* tuple descriptor assigned to it. In this state, tts_isempty must be
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* TRUE, tts_shouldFree FALSE, tts_tuple NULL, tts_buffer InvalidBuffer,
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* and tts_nvalid zero.
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*
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* The tupleDescriptor is simply referenced, not copied, by the TupleTableSlot
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* code. The caller of ExecSetSlotDescriptor() is responsible for providing
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* a descriptor that will live as long as the slot does. (Typically, both
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* slots and descriptors are in per-query memory and are freed by memory
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* context deallocation at query end; so it's not worth providing any extra
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* mechanism to do more. However, the slot will increment the tupdesc
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* reference count if a reference-counted tupdesc is supplied.)
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*
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* When tts_shouldFree is true, the physical tuple is "owned" by the slot
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* and should be freed when the slot's reference to the tuple is dropped.
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*
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* If tts_buffer is not InvalidBuffer, then the slot is holding a pin
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* on the indicated buffer page; drop the pin when we release the
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* slot's reference to that buffer. (tts_shouldFree should always be
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* false in such a case, since presumably tts_tuple is pointing at the
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* buffer page.)
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*
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* tts_nvalid indicates the number of valid columns in the tts_values/isnull
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* arrays. When the slot is holding a "virtual" tuple this must be equal
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* to the descriptor's natts. When the slot is holding a physical tuple
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* this is equal to the number of columns we have extracted (we always
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* extract columns from left to right, so there are no holes).
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*
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* tts_values/tts_isnull are allocated when a descriptor is assigned to the
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* slot; they are of length equal to the descriptor's natts.
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*
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* tts_mintuple must always be NULL if the slot does not hold a "minimal"
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* tuple. When it does, tts_mintuple points to the actual MinimalTupleData
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* object (the thing to be pfree'd if tts_shouldFreeMin is true). If the slot
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* has only a minimal and not also a regular physical tuple, then tts_tuple
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* points at tts_minhdr and the fields of that struct are set correctly
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* for access to the minimal tuple; in particular, tts_minhdr.t_data points
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* MINIMAL_TUPLE_OFFSET bytes before tts_mintuple. This allows column
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* extraction to treat the case identically to regular physical tuples.
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*
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* tts_slow/tts_off are saved state for slot_deform_tuple, and should not
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* be touched by any other code.
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*----------
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*/
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typedef struct TupleTableSlot
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{
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NodeTag type;
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bool tts_isempty; /* true = slot is empty */
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bool tts_shouldFree; /* should pfree tts_tuple? */
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bool tts_shouldFreeMin; /* should pfree tts_mintuple? */
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bool tts_slow; /* saved state for slot_deform_tuple */
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HeapTuple tts_tuple; /* physical tuple, or NULL if virtual */
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TupleDesc tts_tupleDescriptor; /* slot's tuple descriptor */
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MemoryContext tts_mcxt; /* slot itself is in this context */
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Buffer tts_buffer; /* tuple's buffer, or InvalidBuffer */
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int tts_nvalid; /* # of valid values in tts_values */
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Datum *tts_values; /* current per-attribute values */
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bool *tts_isnull; /* current per-attribute isnull flags */
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MinimalTuple tts_mintuple; /* minimal tuple, or NULL if none */
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HeapTupleData tts_minhdr; /* workspace for minimal-tuple-only case */
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long tts_off; /* saved state for slot_deform_tuple */
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} TupleTableSlot;
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#define TTS_HAS_PHYSICAL_TUPLE(slot) \
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((slot)->tts_tuple != NULL && (slot)->tts_tuple != &((slot)->tts_minhdr))
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/*
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* TupIsNull -- is a TupleTableSlot empty?
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*/
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#define TupIsNull(slot) \
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((slot) == NULL || (slot)->tts_isempty)
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/* in executor/execTuples.c */
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extern TupleTableSlot *MakeTupleTableSlot(void);
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extern TupleTableSlot *ExecAllocTableSlot(List **tupleTable);
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extern void ExecResetTupleTable(List *tupleTable, bool shouldFree);
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extern TupleTableSlot *MakeSingleTupleTableSlot(TupleDesc tupdesc);
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extern void ExecDropSingleTupleTableSlot(TupleTableSlot *slot);
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extern void ExecSetSlotDescriptor(TupleTableSlot *slot, TupleDesc tupdesc);
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extern TupleTableSlot *ExecStoreTuple(HeapTuple tuple,
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TupleTableSlot *slot,
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Buffer buffer,
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bool shouldFree);
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extern TupleTableSlot *ExecStoreMinimalTuple(MinimalTuple mtup,
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TupleTableSlot *slot,
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bool shouldFree);
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extern TupleTableSlot *ExecClearTuple(TupleTableSlot *slot);
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extern TupleTableSlot *ExecStoreVirtualTuple(TupleTableSlot *slot);
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extern TupleTableSlot *ExecStoreAllNullTuple(TupleTableSlot *slot);
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extern HeapTuple ExecCopySlotTuple(TupleTableSlot *slot);
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extern MinimalTuple ExecCopySlotMinimalTuple(TupleTableSlot *slot);
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extern HeapTuple ExecFetchSlotTuple(TupleTableSlot *slot);
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extern MinimalTuple ExecFetchSlotMinimalTuple(TupleTableSlot *slot);
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extern Datum ExecFetchSlotTupleDatum(TupleTableSlot *slot);
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extern HeapTuple ExecMaterializeSlot(TupleTableSlot *slot);
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extern TupleTableSlot *ExecCopySlot(TupleTableSlot *dstslot,
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TupleTableSlot *srcslot);
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/* in access/common/heaptuple.c */
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extern Datum slot_getattr(TupleTableSlot *slot, int attnum, bool *isnull);
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extern void slot_getallattrs(TupleTableSlot *slot);
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extern void slot_getsomeattrs(TupleTableSlot *slot, int attnum);
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extern bool slot_attisnull(TupleTableSlot *slot, int attnum);
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#endif /* TUPTABLE_H */
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