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db_include/nodes/params.h

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+/*-------------------------------------------------------------------------
+ *
+ * params.h
+ *	  Support for finding the values associated with Param nodes.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/nodes/params.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PARAMS_H
+#define PARAMS_H
+
+/* Forward declarations, to avoid including other headers */
+struct Bitmapset;
+struct ExprState;
+struct Param;
+struct ParseState;
+
+
+/*
+ *	  ParamListInfo
+ *
+ *	  ParamListInfo structures are used to pass parameters into the executor
+ *	  for parameterized plans.  We support two basic approaches to supplying
+ *	  parameter values, the "static" way and the "dynamic" way.
+ *
+ *	  In the static approach, per-parameter data is stored in an array of
+ *	  ParamExternData structs appended to the ParamListInfo struct.
+ *	  Each entry in the array defines the value to be substituted for a
+ *	  PARAM_EXTERN parameter.  The "paramid" of a PARAM_EXTERN Param
+ *	  can range from 1 to numParams.
+ *
+ *	  Although parameter numbers are normally consecutive, we allow
+ *	  ptype == InvalidOid to signal an unused array entry.
+ *
+ *	  pflags is a flags field.  Currently the only used bit is:
+ *	  PARAM_FLAG_CONST signals the planner that it may treat this parameter
+ *	  as a constant (i.e., generate a plan that works only for this value
+ *	  of the parameter).
+ *
+ *	  In the dynamic approach, all access to parameter values is done through
+ *	  hook functions found in the ParamListInfo struct.  In this case,
+ *	  the ParamExternData array is typically unused and not allocated;
+ *	  but the legal range of paramid is still 1 to numParams.
+ *
+ *	  Although the data structure is really an array, not a list, we keep
+ *	  the old typedef name to avoid unnecessary code changes.
+ *
+ *	  There are 3 hook functions that can be associated with a ParamListInfo
+ *	  structure:
+ *
+ *	  If paramFetch isn't null, it is called to fetch the ParamExternData
+ *	  for a particular param ID, rather than accessing the relevant element
+ *	  of the ParamExternData array.  This supports the case where the array
+ *	  isn't there at all, as well as cases where the data in the array
+ *	  might be obsolete or lazily evaluated.  paramFetch must return the
+ *	  address of a ParamExternData struct describing the specified param ID;
+ *	  the convention above about ptype == InvalidOid signaling an invalid
+ *	  param ID still applies.  The returned struct can either be placed in
+ *	  the "workspace" supplied by the caller, or it can be in storage
+ *	  controlled by the paramFetch hook if that's more convenient.
+ *	  (In either case, the struct is not expected to be long-lived.)
+ *	  If "speculative" is true, the paramFetch hook should not risk errors
+ *	  in trying to fetch the parameter value, and should report an invalid
+ *	  parameter instead.
+ *
+ *	  If paramCompile isn't null, then it controls what execExpr.c compiles
+ *	  for PARAM_EXTERN Param nodes --- typically, this hook would emit a
+ *	  EEOP_PARAM_CALLBACK step.  This allows unnecessary work to be
+ *	  optimized away in compiled expressions.
+ *
+ *	  If parserSetup isn't null, then it is called to re-instantiate the
+ *	  original parsing hooks when a query needs to be re-parsed/planned.
+ *	  This is especially useful if the types of parameters might change
+ *	  from time to time, since it can replace the need to supply a fixed
+ *	  list of parameter types to the parser.
+ *
+ *	  Notice that the paramFetch and paramCompile hooks are actually passed
+ *	  the ParamListInfo struct's address; they can therefore access all
+ *	  three of the "arg" fields, and the distinction between paramFetchArg
+ *	  and paramCompileArg is rather arbitrary.
+ */
+
+#define PARAM_FLAG_CONST	0x0001	/* parameter is constant */
+
+typedef struct ParamExternData
+{
+	Datum		value;			/* parameter value */
+	bool		isnull;			/* is it NULL? */
+	uint16		pflags;			/* flag bits, see above */
+	Oid			ptype;			/* parameter's datatype, or 0 */
+} ParamExternData;
+
+typedef struct ParamListInfoData *ParamListInfo;
+
+typedef ParamExternData *(*ParamFetchHook) (ParamListInfo params,
+											int paramid, bool speculative,
+											ParamExternData *workspace);
+
+typedef void (*ParamCompileHook) (ParamListInfo params, struct Param *param,
+								  struct ExprState *state,
+								  Datum *resv, bool *resnull);
+
+typedef void (*ParserSetupHook) (struct ParseState *pstate, void *arg);
+
+typedef struct ParamListInfoData
+{
+	ParamFetchHook paramFetch;	/* parameter fetch hook */
+	void	   *paramFetchArg;
+	ParamCompileHook paramCompile;	/* parameter compile hook */
+	void	   *paramCompileArg;
+	ParserSetupHook parserSetup;	/* parser setup hook */
+	void	   *parserSetupArg;
+	char	   *paramValuesStr; /* params as a single string for errors */
+	int			numParams;		/* nominal/maximum # of Params represented */
+
+	/*
+	 * params[] may be of length zero if paramFetch is supplied; otherwise it
+	 * must be of length numParams.
+	 */
+	ParamExternData params[FLEXIBLE_ARRAY_MEMBER];
+}			ParamListInfoData;
+
+
+/* ----------------
+ *	  ParamExecData
+ *
+ *	  ParamExecData entries are used for executor internal parameters
+ *	  (that is, values being passed into or out of a sub-query).  The
+ *	  paramid of a PARAM_EXEC Param is a (zero-based) index into an
+ *	  array of ParamExecData records, which is referenced through
+ *	  es_param_exec_vals or ecxt_param_exec_vals.
+ *
+ *	  If execPlan is not NULL, it points to a SubPlanState node that needs
+ *	  to be executed to produce the value.  (This is done so that we can have
+ *	  lazy evaluation of InitPlans: they aren't executed until/unless a
+ *	  result value is needed.)	Otherwise the value is assumed to be valid
+ *	  when needed.
+ * ----------------
+ */
+
+typedef struct ParamExecData
+{
+	void	   *execPlan;		/* should be "SubPlanState *" */
+	Datum		value;
+	bool		isnull;
+} ParamExecData;
+
+/* type of argument for ParamsErrorCallback */
+typedef struct ParamsErrorCbData
+{
+	const char *portalName;
+	ParamListInfo params;
+} ParamsErrorCbData;
+
+/* Functions found in src/backend/nodes/params.c */
+extern ParamListInfo makeParamList(int numParams);
+extern ParamListInfo copyParamList(ParamListInfo from);
+extern Size EstimateParamListSpace(ParamListInfo paramLI);
+extern void SerializeParamList(ParamListInfo paramLI, char **start_address);
+extern ParamListInfo RestoreParamList(char **start_address);
+extern char *BuildParamLogString(ParamListInfo params, char **paramTextValues,
+								 int valueLen);
+extern void ParamsErrorCallback(void *arg);
+
+#endif							/* PARAMS_H */