EVOLUTION-NINJA

Edit File: tuptable.h

/*------------------------------------------------------------------------- * * tuptable.h * tuple table support stuff * * * Portions Copyright (c) 1996-2012, 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 "storage/buf.h" /*---------- * The executor stores tuples in a "tuple table" which is a List of * independent TupleTableSlots. There are several cases we need to handle: * 1. physical tuple in a disk buffer page * 2. physical tuple constructed in palloc'ed memory * 3. "minimal" physical tuple constructed in palloc'ed memory * 4. "virtual" tuple consisting of Datum/isnull arrays * * 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. Any pass-by-reference Datums in the * tuple 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. We only use virtual * tuples in the result slots of plan nodes --- tuples to be copied anywhere * else need to be "materialized" into physical tuples. Note also that a * virtual tuple does not have any "system columns". * * It is also possible for a TupleTableSlot to hold both physical and minimal * copies of a tuple. This is done when the slot is requested to provide * the format other than the one it currently holds. (Originally we attempted * to handle such requests by replacing one format with the other, but that * had the fatal defect of invalidating any pass-by-reference Datums pointing * into the existing slot contents.) Both copies must contain identical data * payloads when this is the case. * * The Datum/isnull arrays of a TupleTableSlot serve double duty. When the * slot contains a virtual tuple, they are the authoritative data. When the * slot contains a physical tuple, 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", 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_isempty must be * TRUE, tts_shouldFree FALSE, tts_tuple NULL, tts_buffer InvalidBuffer, * 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 true, the physical tuple is "owned" by the slot * and should be freed when the slot's reference to the tuple is dropped. * * If tts_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_shouldFree should always be * false in such a case, since presumably tts_tuple is pointing at the * buffer page.) * * tts_nvalid indicates the number of valid columns in the tts_values/isnull * arrays. When the slot is holding a "virtual" tuple this must be equal * to the descriptor's natts. When the slot is holding a physical tuple * this is equal to the number of columns we have extracted (we always * extract columns from left to right, so there are no holes). * * tts_values/tts_isnull are allocated when a descriptor is assigned to the * slot; they are of length equal to the descriptor's natts. * * tts_mintuple must always be NULL if the slot does not hold a "minimal" * tuple. When it does, tts_mintuple points to the actual MinimalTupleData * object (the thing to be pfree'd if tts_shouldFreeMin is true). If the slot * has only a minimal and not also a regular physical tuple, then tts_tuple * points at tts_minhdr and the fields of that struct are set correctly * for access to the minimal tuple; in particular, tts_minhdr.t_data points * MINIMAL_TUPLE_OFFSET bytes before tts_mintuple. This allows column * extraction to treat the case identically to regular physical tuples. * * tts_slow/tts_off are saved state for slot_deform_tuple, and should not * be touched by any other code. *---------- */ typedef struct TupleTableSlot { NodeTag type; bool tts_isempty; /* true = slot is empty */ bool tts_shouldFree; /* should pfree tts_tuple? */ bool tts_shouldFreeMin; /* should pfree tts_mintuple? */ bool tts_slow; /* saved state for slot_deform_tuple */ HeapTuple tts_tuple; /* physical tuple, or NULL if virtual */ TupleDesc tts_tupleDescriptor; /* slot's tuple descriptor */ MemoryContext tts_mcxt; /* slot itself is in this context */ Buffer tts_buffer; /* tuple's buffer, or InvalidBuffer */ int tts_nvalid; /* # of valid values in tts_values */ Datum *tts_values; /* current per-attribute values */ bool *tts_isnull; /* current per-attribute isnull flags */ MinimalTuple tts_mintuple; /* minimal tuple, or NULL if none */ HeapTupleData tts_minhdr; /* workspace for minimal-tuple-only case */ long tts_off; /* saved state for slot_deform_tuple */ } TupleTableSlot; #define TTS_HAS_PHYSICAL_TUPLE(slot) \ ((slot)->tts_tuple != NULL && (slot)->tts_tuple != &((slot)->tts_minhdr)) /* * TupIsNull -- is a TupleTableSlot empty? */ #define TupIsNull(slot) \ ((slot) == NULL || (slot)->tts_isempty) /* in executor/execTuples.c */ extern TupleTableSlot *MakeTupleTableSlot(void); extern TupleTableSlot *ExecAllocTableSlot(List **tupleTable); extern void ExecResetTupleTable(List *tupleTable, bool shouldFree); extern TupleTableSlot *MakeSingleTupleTableSlot(TupleDesc tupdesc); extern void ExecDropSingleTupleTableSlot(TupleTableSlot *slot); extern void ExecSetSlotDescriptor(TupleTableSlot *slot, TupleDesc tupdesc); extern TupleTableSlot *ExecStoreTuple(HeapTuple tuple, TupleTableSlot *slot, Buffer buffer, bool shouldFree); extern TupleTableSlot *ExecStoreMinimalTuple(MinimalTuple mtup, TupleTableSlot *slot, bool shouldFree); extern TupleTableSlot *ExecClearTuple(TupleTableSlot *slot); extern TupleTableSlot *ExecStoreVirtualTuple(TupleTableSlot *slot); extern TupleTableSlot *ExecStoreAllNullTuple(TupleTableSlot *slot); extern HeapTuple ExecCopySlotTuple(TupleTableSlot *slot); extern MinimalTuple ExecCopySlotMinimalTuple(TupleTableSlot *slot); extern HeapTuple ExecFetchSlotTuple(TupleTableSlot *slot); extern MinimalTuple ExecFetchSlotMinimalTuple(TupleTableSlot *slot); extern Datum ExecFetchSlotTupleDatum(TupleTableSlot *slot); extern HeapTuple ExecMaterializeSlot(TupleTableSlot *slot); extern TupleTableSlot *ExecCopySlot(TupleTableSlot *dstslot, TupleTableSlot *srcslot); /* in access/common/heaptuple.c */ extern Datum slot_getattr(TupleTableSlot *slot, int attnum, bool *isnull); extern void slot_getallattrs(TupleTableSlot *slot); extern void slot_getsomeattrs(TupleTableSlot *slot, int attnum); extern bool slot_attisnull(TupleTableSlot *slot, int attnum); #endif /* TUPTABLE_H */