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/*-------------------------------------------------------------------------
*
* params.h
* Support for finding the values associated with Param nodes.
*
*
* Portions Copyright (c) 1996-2018, 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;
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;
/* Functions found in src/backend/nodes/params.c */
extern ParamListInfo copyParamList(ParamListInfo from);
extern Size EstimateParamListSpace(ParamListInfo paramLI);
extern void SerializeParamList(ParamListInfo paramLI, char **start_address);
extern ParamListInfo RestoreParamList(char **start_address);
#endif /* PARAMS_H */
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