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are now both invoked once per received SQL command (raw parsetree) from pg_exec_query_string. BeginCommand is actually just an empty routine at the moment --- all its former operations have been pushed into tuple receiver setup routines in printtup.c. This makes for a clean distinction between BeginCommand/EndCommand (once per command) and the tuple receiver setup/teardown routines (once per ExecutorRun call), whereas the old code was quite ad hoc. Along the way, clean up the calling conventions for ExecutorRun a little bit.
109 lines
3.8 KiB
C
109 lines
3.8 KiB
C
/*-------------------------------------------------------------------------
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*
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* dest.h
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* support for communication destinations
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*
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* Whenever the backend executes a query, the results
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* have to go someplace.
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*
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* - stdout is the destination only when we are running a
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* standalone backend (no postmaster) and are returning results
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* back to an interactive user.
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*
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* - a remote process is the destination when we are
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* running a backend with a frontend and the frontend executes
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* PQexec() or PQfn(). In this case, the results are sent
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* to the frontend via the functions in backend/libpq.
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*
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* - None is the destination when the system executes
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* a query internally. The results are discarded.
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*
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* dest.c defines three functions that implement destination management:
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*
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* BeginCommand: initialize the destination at start of command.
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* DestToFunction: return a pointer to a struct of destination-specific
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* receiver functions.
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* EndCommand: clean up the destination at end of command.
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*
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* BeginCommand/EndCommand are executed once per received SQL query.
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*
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* DestToFunction, and the receiver functions it links to, are executed
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* each time we run the executor to produce tuples, which may occur
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* multiple times per received query (eg, due to additional queries produced
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* by rewrite rules).
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*
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* The DestReceiver object returned by DestToFunction may be a statically
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* allocated object (for destination types that require no local state)
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* or can be a palloc'd object that has DestReceiver as its first field
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* and contains additional fields (see printtup.c for an example). These
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* additional fields are then accessible to the DestReceiver functions
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* by casting the DestReceiver* pointer passed to them.
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* The palloc'd object is pfree'd by the DestReceiver's cleanup function.
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*
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*
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* Portions Copyright (c) 1996-2001, 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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* $Id: dest.h,v 1.30 2002/02/27 19:36:13 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef DEST_H
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#define DEST_H
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#include "access/htup.h"
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/* buffer size to use for command completion tags */
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#define COMPLETION_TAG_BUFSIZE 64
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/* ----------------
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* CommandDest is a simplistic means of identifying the desired
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* destination. Someday this will probably need to be improved.
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* ----------------
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*/
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typedef enum
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{
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None, /* results are discarded */
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Debug, /* results go to debugging output */
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Remote, /* results sent to frontend process */
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RemoteInternal, /* results sent to frontend process in
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* internal (binary) form */
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SPI /* results sent to SPI manager */
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} CommandDest;
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/* ----------------
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* DestReceiver is a base type for destination-specific local state.
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* In the simplest cases, there is no state info, just the function
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* pointers that the executor must call.
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* ----------------
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*/
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typedef struct _DestReceiver DestReceiver;
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struct _DestReceiver
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{
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/* Called for each tuple to be output: */
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void (*receiveTuple) (HeapTuple tuple, TupleDesc typeinfo,
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DestReceiver *self);
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/* Initialization and teardown: */
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void (*setup) (DestReceiver *self, int operation,
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const char *portalName, TupleDesc typeinfo);
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void (*cleanup) (DestReceiver *self);
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/* Private fields might appear beyond this point... */
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};
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/* The primary destination management functions */
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extern void BeginCommand(const char *commandTag, CommandDest dest);
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extern DestReceiver *DestToFunction(CommandDest dest);
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extern void EndCommand(const char *commandTag, CommandDest dest);
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/* Additional functions that go with destination management, more or less. */
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extern void SendCopyBegin(void);
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extern void ReceiveCopyBegin(void);
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extern void NullCommand(CommandDest dest);
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extern void ReadyForQuery(CommandDest dest);
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#endif /* DEST_H */
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