spi_priv.h

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/*-------------------------------------------------------------------------
 *
 * spi_priv.h
 *              Server Programming Interface private declarations
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/executor/spi_priv.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef SPI_PRIV_H
#define SPI_PRIV_H

#include "executor/spi.h"


#define _SPI_PLAN_MAGIC     569278163

typedef struct
{
    /* current results */
    uint32      processed;      /* by Executor */
    Oid         lastoid;
    SPITupleTable *tuptable;

    MemoryContext procCxt;      /* procedure context */
    MemoryContext execCxt;      /* executor context */
    MemoryContext savedcxt;     /* context of SPI_connect's caller */
    SubTransactionId connectSubid;      /* ID of connecting subtransaction */
} _SPI_connection;

/*
 * SPI plans have three states: saved, unsaved, or temporary.
 *
 * Ordinarily, the _SPI_plan struct itself as well as the argtypes array
 * are in a dedicated memory context identified by plancxt (which can be
 * really small).  All the other subsidiary state is in plancache entries
 * identified by plancache_list (note: the list cells themselves are in
 * plancxt).
 *
 * In an unsaved plan, the plancxt as well as the plancache entries' contexts
 * are children of the SPI procedure context, so they'll all disappear at
 * function exit.  plancache.c also knows that the plancache entries are
 * "unsaved", so it doesn't link them into its global list; hence they do
 * not respond to inval events.  This is OK since we are presumably holding
 * adequate locks to prevent other backends from messing with the tables.
 *
 * For a saved plan, the plancxt is made a child of CacheMemoryContext
 * since it should persist until explicitly destroyed.  Likewise, the
 * plancache entries will be under CacheMemoryContext since we tell
 * plancache.c to save them.  We rely on plancache.c to keep the cache
 * entries up-to-date as needed in the face of invalidation events.
 *
 * There are also "temporary" SPI plans, in which the _SPI_plan struct is
 * not even palloc'd but just exists in some function's local variable.
 * The plancache entries are unsaved and exist under the SPI executor context,
 * while additional data such as argtypes and list cells is loose in the SPI
 * executor context.  Such plans can be identified by having plancxt == NULL.
 *
 * We can also have "one-shot" SPI plans (which are typically temporary,
 * as described above).  These are meant to be executed once and discarded,
 * and various optimizations are made on the assumption of single use.
 * Note in particular that the CachedPlanSources within such an SPI plan
 * are not "complete" until execution.
 *
 * Note: if the original query string contained only whitespace and comments,
 * the plancache_list will be NIL and so there is no place to store the
 * query string.  We don't care about that, but we do care about the
 * argument type array, which is why it's seemingly-redundantly stored.
 */
typedef struct _SPI_plan
{
    int         magic;          /* should equal _SPI_PLAN_MAGIC */
    bool        saved;          /* saved or unsaved plan? */
    bool        oneshot;        /* one-shot plan? */
    List       *plancache_list; /* one CachedPlanSource per parsetree */
    MemoryContext plancxt;      /* Context containing _SPI_plan and data */
    int         cursor_options; /* Cursor options used for planning */
    int         nargs;          /* number of plan arguments */
    Oid        *argtypes;       /* Argument types (NULL if nargs is 0) */
    ParserSetupHook parserSetup;    /* alternative parameter spec method */
    void       *parserSetupArg;
} _SPI_plan;

#endif   /* SPI_PRIV_H */