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/*-------------------------------------------------------------------------
*
* dest.h
* support for communication destinations
*
* Whenever the backend executes a query, the results
* have to go someplace.
*
* - stdout is the destination only when we are running a
* standalone backend (no postmaster) and are returning results
* back to an interactive user.
*
* - a remote process 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 functions in backend/libpq.
*
* - None is the destination when the system executes
* a query internally. The results are discarded.
*
* dest.c defines three functions that implement destination management:
*
* BeginCommand: initialize the destination at start of command.
* DestToFunction: return a pointer to a struct of destination-specific
* receiver functions.
* EndCommand: clean up the destination at end of command.
*
* BeginCommand/EndCommand are executed once per received SQL query.
*
* DestToFunction, and the receiver functions it links to, are executed
* each time we run the executor to produce tuples, which may occur
* multiple times per received query (eg, due to additional queries produced
* by rewrite rules).
*
* 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.
*
*
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: dest.h,v 1.35 2003/05/05 00:44:56 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#ifndef DEST_H
#define DEST_H
#include "access/htup.h"
/* buffer size to use for command completion tags */
#define COMPLETION_TAG_BUFSIZE 64
/* ----------------
* CommandDest is a simplistic means of identifying the desired
* destination. Someday this will probably need to be improved.
*
* Note: only the values None, Debug, Remote are legal for the global
* variable whereToSendOutput. The other values may be selected
* as the destination for individual commands.
* ----------------
*/
typedef enum
{
None, /* results are discarded */
Debug, /* results go to debugging output */
Remote, /* results sent to frontend process */
RemoteInternal, /* results sent to frontend process in
* internal (binary) form */
SPI, /* results sent to SPI manager */
Tuplestore, /* results sent to Tuplestore */
RemoteExecute, /* sent to frontend, in Execute command */
RemoteExecuteInternal /* same, but binary format */
} 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, int operation,
const char *portalName, TupleDesc typeinfo);
void (*cleanup) (DestReceiver *self);
/* Private fields might appear beyond this point... */
};
/* The primary destination management functions */
extern void BeginCommand(const char *commandTag, CommandDest dest);
extern DestReceiver *DestToFunction(CommandDest dest);
extern void EndCommand(const char *commandTag, CommandDest dest);
/* Additional functions that go with destination management, more or less. */
extern void NullCommand(CommandDest dest);
extern void ReadyForQuery(CommandDest dest);
#endif /* DEST_H */
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