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PostgreSQL/src/include/executor/spi.h
Tom Lane 2f48ede080 Avoid using a cursor in plpgsql's RETURN QUERY statement. 
plpgsql has always executed the query given in a RETURN QUERY command
by opening it as a cursor and then fetching a few rows at a time,
which it turns around and dumps into the function's result tuplestore.
The point of this was to keep from blowing out memory with an oversized
SPITupleTable result (note that while a tuplestore can spill tuples
to disk, SPITupleTable cannot).  However, it's rather inefficient, both
because of extra data copying and because of executor entry/exit
overhead.  In recent versions, a new performance problem has emerged:
use of a cursor prevents use of a parallel plan for the executed query.

We can improve matters by skipping use of a cursor and having the
executor push result tuples directly into the function's result
tuplestore.  However, a moderate amount of new infrastructure is needed
to make that idea work:

* We can use the existing tstoreReceiver.c DestReceiver code to funnel
executor output to the tuplestore, but it has to be extended to support
plpgsql's requirement for possibly applying a tuple conversion map.

* SPI needs to be extended to allow use of a caller-supplied
DestReceiver instead of its usual receiver that puts tuples into
a SPITupleTable.  Two new API calls are needed to handle both the
RETURN QUERY and RETURN QUERY EXECUTE cases.

I also felt that I didn't want these new API calls to use the legacy
method of specifying query parameter values with "char" null flags
(the old ' '/'n' convention); rather they should accept ParamListInfo
objects containing the parameter type and value info.  This required
a bit of additional new infrastructure since we didn't yet have any
parse analysis callback that would interpret $N parameter symbols
according to type data supplied in a ParamListInfo.  There seems to be
no harm in letting makeParamList install that callback by default,
rather than leaving a new ParamListInfo's parserSetup hook as NULL.
(Indeed, as of HEAD, I couldn't find anyplace that was using the
parserSetup field at all; plpgsql was using parserSetupArg for its
own purposes, but parserSetup seemed to be write-only.)

We can actually get plpgsql out of the business of using legacy null
flags altogether, and using ParamListInfo instead of its ad-hoc
PreparedParamsData structure; but this requires inventing one more
SPI API call that can replace SPI_cursor_open_with_args.  That seems
worth doing, though.

SPI_execute_with_args and SPI_cursor_open_with_args are now unused
anywhere in the core PG distribution.  Perhaps someday we could
deprecate/remove them.  But cleaning up the crufty bits of the SPI
API is a task for a different patch.

Per bug #16040 from Jeremy Smith.  This is unfortunately too invasive to
consider back-patching.  Patch by me; thanks to Hamid Akhtar for review.

Discussion: https://postgr.es/m/16040-eaacad11fecfb198@postgresql.org
2020-06-12 12:14:32 -04:00

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/*-------------------------------------------------------------------------
*
* spi.h
* Server Programming Interface public declarations
*
* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/executor/spi.h
*
*-------------------------------------------------------------------------
*/
#ifndef SPI_H
#define SPI_H
#include "commands/trigger.h"
#include "lib/ilist.h"
#include "nodes/parsenodes.h"
#include "utils/portal.h"
typedef struct SPITupleTable
{
/* Public members */
TupleDesc tupdesc; /* tuple descriptor */
HeapTuple *vals; /* array of tuples */
uint64 numvals; /* number of valid tuples */
/* Private members, not intended for external callers */
uint64 alloced; /* allocated length of vals array */
MemoryContext tuptabcxt; /* memory context of result table */
slist_node next; /* link for internal bookkeeping */
SubTransactionId subid; /* subxact in which tuptable was created */
} SPITupleTable;
/* Plans are opaque structs for standard users of SPI */
typedef struct _SPI_plan *SPIPlanPtr;
#define SPI_ERROR_CONNECT (-1)
#define SPI_ERROR_COPY (-2)
#define SPI_ERROR_OPUNKNOWN (-3)
#define SPI_ERROR_UNCONNECTED (-4)
#define SPI_ERROR_CURSOR (-5) /* not used anymore */
#define SPI_ERROR_ARGUMENT (-6)
#define SPI_ERROR_PARAM (-7)
#define SPI_ERROR_TRANSACTION (-8)
#define SPI_ERROR_NOATTRIBUTE (-9)
#define SPI_ERROR_NOOUTFUNC (-10)
#define SPI_ERROR_TYPUNKNOWN (-11)
#define SPI_ERROR_REL_DUPLICATE (-12)
#define SPI_ERROR_REL_NOT_FOUND (-13)
#define SPI_OK_CONNECT 1
#define SPI_OK_FINISH 2
#define SPI_OK_FETCH 3
#define SPI_OK_UTILITY 4
#define SPI_OK_SELECT 5
#define SPI_OK_SELINTO 6
#define SPI_OK_INSERT 7
#define SPI_OK_DELETE 8
#define SPI_OK_UPDATE 9
#define SPI_OK_CURSOR 10
#define SPI_OK_INSERT_RETURNING 11
#define SPI_OK_DELETE_RETURNING 12
#define SPI_OK_UPDATE_RETURNING 13
#define SPI_OK_REWRITTEN 14
#define SPI_OK_REL_REGISTER 15
#define SPI_OK_REL_UNREGISTER 16
#define SPI_OK_TD_REGISTER 17
#define SPI_OPT_NONATOMIC (1 << 0)
/* These used to be functions, now just no-ops for backwards compatibility */
#define SPI_push() ((void) 0)
#define SPI_pop() ((void) 0)
#define SPI_push_conditional() false
#define SPI_pop_conditional(pushed) ((void) 0)
#define SPI_restore_connection() ((void) 0)
extern PGDLLIMPORT uint64 SPI_processed;
extern PGDLLIMPORT SPITupleTable *SPI_tuptable;
extern PGDLLIMPORT int SPI_result;
extern int SPI_connect(void);
extern int SPI_connect_ext(int options);
extern int SPI_finish(void);
extern int SPI_execute(const char *src, bool read_only, long tcount);
extern int SPI_execute_plan(SPIPlanPtr plan, Datum *Values, const char *Nulls,
bool read_only, long tcount);
extern int SPI_execute_plan_with_paramlist(SPIPlanPtr plan,
ParamListInfo params,
bool read_only, long tcount);
extern int SPI_execute_plan_with_receiver(SPIPlanPtr plan,
ParamListInfo params,
bool read_only, long tcount,
DestReceiver *dest);
extern int SPI_exec(const char *src, long tcount);
extern int SPI_execp(SPIPlanPtr plan, Datum *Values, const char *Nulls,
long tcount);
extern int SPI_execute_snapshot(SPIPlanPtr plan,
Datum *Values, const char *Nulls,
Snapshot snapshot,
Snapshot crosscheck_snapshot,
bool read_only, bool fire_triggers, long tcount);
extern int SPI_execute_with_args(const char *src,
int nargs, Oid *argtypes,
Datum *Values, const char *Nulls,
bool read_only, long tcount);
extern int SPI_execute_with_receiver(const char *src,
ParamListInfo params,
bool read_only, long tcount,
DestReceiver *dest);
extern SPIPlanPtr SPI_prepare(const char *src, int nargs, Oid *argtypes);
extern SPIPlanPtr SPI_prepare_cursor(const char *src, int nargs, Oid *argtypes,
int cursorOptions);
extern SPIPlanPtr SPI_prepare_params(const char *src,
ParserSetupHook parserSetup,
void *parserSetupArg,
int cursorOptions);
extern int SPI_keepplan(SPIPlanPtr plan);
extern SPIPlanPtr SPI_saveplan(SPIPlanPtr plan);
extern int SPI_freeplan(SPIPlanPtr plan);
extern Oid SPI_getargtypeid(SPIPlanPtr plan, int argIndex);
extern int SPI_getargcount(SPIPlanPtr plan);
extern bool SPI_is_cursor_plan(SPIPlanPtr plan);
extern bool SPI_plan_is_valid(SPIPlanPtr plan);
extern const char *SPI_result_code_string(int code);
extern List *SPI_plan_get_plan_sources(SPIPlanPtr plan);
extern CachedPlan *SPI_plan_get_cached_plan(SPIPlanPtr plan);
extern HeapTuple SPI_copytuple(HeapTuple tuple);
extern HeapTupleHeader SPI_returntuple(HeapTuple tuple, TupleDesc tupdesc);
extern HeapTuple SPI_modifytuple(Relation rel, HeapTuple tuple, int natts,
int *attnum, Datum *Values, const char *Nulls);
extern int SPI_fnumber(TupleDesc tupdesc, const char *fname);
extern char *SPI_fname(TupleDesc tupdesc, int fnumber);
extern char *SPI_getvalue(HeapTuple tuple, TupleDesc tupdesc, int fnumber);
extern Datum SPI_getbinval(HeapTuple tuple, TupleDesc tupdesc, int fnumber, bool *isnull);
extern char *SPI_gettype(TupleDesc tupdesc, int fnumber);
extern Oid SPI_gettypeid(TupleDesc tupdesc, int fnumber);
extern char *SPI_getrelname(Relation rel);
extern char *SPI_getnspname(Relation rel);
extern void *SPI_palloc(Size size);
extern void *SPI_repalloc(void *pointer, Size size);
extern void SPI_pfree(void *pointer);
extern Datum SPI_datumTransfer(Datum value, bool typByVal, int typLen);
extern void SPI_freetuple(HeapTuple pointer);
extern void SPI_freetuptable(SPITupleTable *tuptable);
extern Portal SPI_cursor_open(const char *name, SPIPlanPtr plan,
Datum *Values, const char *Nulls, bool read_only);
extern Portal SPI_cursor_open_with_args(const char *name,
const char *src,
int nargs, Oid *argtypes,
Datum *Values, const char *Nulls,
bool read_only, int cursorOptions);
extern Portal SPI_cursor_open_with_paramlist(const char *name, SPIPlanPtr plan,
ParamListInfo params, bool read_only);
extern Portal SPI_cursor_parse_open_with_paramlist(const char *name,
const char *src,
ParamListInfo params,
bool read_only,
int cursorOptions);
extern Portal SPI_cursor_find(const char *name);
extern void SPI_cursor_fetch(Portal portal, bool forward, long count);
extern void SPI_cursor_move(Portal portal, bool forward, long count);
extern void SPI_scroll_cursor_fetch(Portal, FetchDirection direction, long count);
extern void SPI_scroll_cursor_move(Portal, FetchDirection direction, long count);
extern void SPI_cursor_close(Portal portal);
extern int SPI_register_relation(EphemeralNamedRelation enr);
extern int SPI_unregister_relation(const char *name);
extern int SPI_register_trigger_data(TriggerData *tdata);
extern void SPI_start_transaction(void);
extern void SPI_commit(void);
extern void SPI_commit_and_chain(void);
extern void SPI_rollback(void);
extern void SPI_rollback_and_chain(void);
extern void SPICleanup(void);
extern void AtEOXact_SPI(bool isCommit);
extern void AtEOSubXact_SPI(bool isCommit, SubTransactionId mySubid);
extern bool SPI_inside_nonatomic_context(void);
#endif /* SPI_H */
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