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/*-------------------------------------------------------------------------
*
* dest.h
* Whenever the backend executes a query, the results
* have to go someplace - either to the standard output,
* to a local portal buffer or to a remote portal buffer.
*
* - stdout is the destination only when we are running a
* backend without a postmaster and are returning results
* back to the user.
*
* - a local portal buffer is the destination when a backend
* executes a user-defined function which calls PQexec() or
* PQfn(). In this case, the results are collected into a
* PortalBuffer which the user's function may diddle with.
*
* - a remote portal buffer is the destination when we are
* running a backend with a frontend and the frontend executes
* PQexec() or PQfn(). In this case, the results are sent
* to the frontend via the pq_ functions.
*
* - None is the destination when the system executes
* a query internally. This is not used now but it may be
* useful for the parallel optimiser/executor.
*
* dest.c defines three functions that implement destination management:
*
* BeginCommand: initialize the destination.
* DestToFunction: return a pointer to a struct of destination-specific
* receiver functions.
* EndCommand: clean up the destination when output is complete.
*
* The DestReceiver object returned by DestToFunction may be a statically
* allocated object (for destination types that require no local state)
* or can be a palloc'd object that has DestReceiver as its first field
* and contains additional fields (see printtup.c for an example). These
* additional fields are then accessible to the DestReceiver functions
* by casting the DestReceiver* pointer passed to them.
* The palloc'd object is pfree'd by the DestReceiver's cleanup function.
*
* XXX FIXME: the initialization and cleanup code that currently appears
* in-line in BeginCommand and EndCommand probably should be moved out
* to routines associated with each destination receiver type.
*
* Copyright (c) 1994, Regents of the University of California
*
* $Id: dest.h,v 1.22 1999/07/15 23:04:17 momjian Exp $
*
*-------------------------------------------------------------------------
*/
#ifndef DEST_H
#define DEST_H
#include "access/htup.h"
/* ----------------
* CommandDest is a simplistic means of identifying the desired
* destination. Someday this will probably need to be improved.
* ----------------
*/
typedef enum
{
None, /* results are discarded */
Debug, /* results go to debugging output */
Local, /* results go in local portal buffer */
Remote, /* results sent to frontend process */
RemoteInternal, /* results sent to frontend process in
* internal (binary) form */
SPI /* results sent to SPI manager */
} CommandDest;
/* ----------------
* DestReceiver is a base type for destination-specific local state.
* In the simplest cases, there is no state info, just the function
* pointers that the executor must call.
* ----------------
*/
typedef struct _DestReceiver DestReceiver;
struct _DestReceiver
{
/* Called for each tuple to be output: */
void (*receiveTuple) (HeapTuple tuple, TupleDesc typeinfo,
DestReceiver *self);
/* Initialization and teardown: */
void (*setup) (DestReceiver *self, TupleDesc typeinfo);
void (*cleanup) (DestReceiver *self);
/* Private fields might appear beyond this point... */
};
/* The primary destination management functions */
extern void BeginCommand(char *pname, int operation, TupleDesc attinfo,
bool isIntoRel, bool isIntoPortal, char *tag,
CommandDest dest);
extern DestReceiver *DestToFunction(CommandDest dest);
extern void EndCommand(char *commandTag, CommandDest dest);
/* Additional functions that go with destination management, more or less. */
extern void SendCopyBegin(void);
extern void ReceiveCopyBegin(void);
extern void NullCommand(CommandDest dest);
extern void ReadyForQuery(CommandDest dest);
extern void UpdateCommandInfo(int operation, Oid lastoid, uint32 tuples);
#endif /* DEST_H */
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