src/include/utils/portal.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * portal.h
   4  *        POSTGRES portal definitions.
   5  *
   6  * A portal is an abstraction which represents the execution state of
   7  * a running or runnable query.  Portals support both SQL-level CURSORs
   8  * and protocol-level portals.
   9  *
  10  * Scrolling (nonsequential access) and suspension of execution are allowed
  11  * only for portals that contain a single SELECT-type query.  We do not want
  12  * to let the client suspend an update-type query partway through!      Because
  13  * the query rewriter does not allow arbitrary ON SELECT rewrite rules,
  14  * only queries that were originally update-type could produce multiple
  15  * plan trees; so the restriction to a single query is not a problem
  16  * in practice.
  17  *
  18  * For SQL cursors, we support three kinds of scroll behavior:
  19  *
  20  * (1) Neither NO SCROLL nor SCROLL was specified: to remain backward
  21  *         compatible, we allow backward fetches here, unless it would
  22  *         impose additional runtime overhead to do so.
  23  *
  24  * (2) NO SCROLL was specified: don't allow any backward fetches.
  25  *
  26  * (3) SCROLL was specified: allow all kinds of backward fetches, even
  27  *         if we need to take a performance hit to do so.  (The planner sticks
  28  *         a Materialize node atop the query plan if needed.)
  29  *
  30  * Case #1 is converted to #2 or #3 by looking at the query itself and
  31  * determining if scrollability can be supported without additional
  32  * overhead.
  33  *
  34  * Protocol-level portals have no nonsequential-fetch API and so the
  35  * distinction doesn't matter for them.  They are always initialized
  36  * to look like NO SCROLL cursors.
  37  *
  38  *
  39  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  40  * Portions Copyright (c) 1994, Regents of the University of California
  41  *
  42  * $PostgreSQL$
  43  *
  44  *-------------------------------------------------------------------------
  45  */
  46 #ifndef PORTAL_H
  47 #define PORTAL_H
  48
  49 #include "executor/execdesc.h"
  50 #include "utils/resowner.h"
  51 #include "utils/timestamp.h"
  52
  53 /*
  54  * We have several execution strategies for Portals, depending on what
  55  * query or queries are to be executed.  (Note: in all cases, a Portal
  56  * executes just a single source-SQL query, and thus produces just a
  57  * single result from the user's viewpoint.  However, the rule rewriter
  58  * may expand the single source query to zero or many actual queries.)
  59  *
  60  * PORTAL_ONE_SELECT: the portal contains one single SELECT query.      We run
  61  * the Executor incrementally as results are demanded.  This strategy also
  62  * supports holdable cursors (the Executor results can be dumped into a
  63  * tuplestore for access after transaction completion).
  64  *
  65  * PORTAL_ONE_RETURNING: the portal contains a single INSERT/UPDATE/DELETE
  66  * query with a RETURNING clause (plus possibly auxiliary queries added by
  67  * rule rewriting).  On first execution, we run the portal to completion
  68  * and dump the primary query's results into the portal tuplestore; the
  69  * results are then returned to the client as demanded.  (We can't support
  70  * suspension of the query partway through, because the AFTER TRIGGER code
  71  * can't cope, and also because we don't want to risk failing to execute
  72  * all the auxiliary queries.)
  73  *
  74  * PORTAL_UTIL_SELECT: the portal contains a utility statement that returns
  75  * a SELECT-like result (for example, EXPLAIN or SHOW).  On first execution,
  76  * we run the statement and dump its results into the portal tuplestore;
  77  * the results are then returned to the client as demanded.
  78  *
  79  * PORTAL_MULTI_QUERY: all other cases.  Here, we do not support partial
  80  * execution: the portal's queries will be run to completion on first call.
  81  */
  82 typedef enum PortalStrategy
  83 {
  84         PORTAL_ONE_SELECT,
  85         PORTAL_ONE_RETURNING,
  86         PORTAL_UTIL_SELECT,
  87         PORTAL_MULTI_QUERY
  88 } PortalStrategy;
  89
  90 /*
  91  * A portal is always in one of these states.  It is possible to transit
  92  * from ACTIVE back to READY if the query is not run to completion;
  93  * otherwise we never back up in status.
  94  */
  95 typedef enum PortalStatus
  96 {
  97         PORTAL_NEW,                                     /* freshly created */
  98         PORTAL_DEFINED,                         /* PortalDefineQuery done */
  99         PORTAL_READY,                           /* PortalStart complete, can run it */
 100         PORTAL_ACTIVE,                          /* portal is running (can't delete it) */
 101         PORTAL_DONE,                            /* portal is finished (don't re-run it) */
 102         PORTAL_FAILED                           /* portal got error (can't re-run it) */
 103 } PortalStatus;
 104
 105 /*
 106  * Note: typedef Portal is declared in tcop/dest.h as
 107  *              typedef struct PortalData *Portal;
 108  */
 109
 110 typedef struct PortalData
 111 {
 112         /* Bookkeeping data */
 113         const char *name;                       /* portal's name */
 114         const char *prepStmtName;       /* source prepared statement (NULL if none) */
 115         MemoryContext heap;                     /* subsidiary memory for portal */
 116         ResourceOwner resowner;         /* resources owned by portal */
 117         void            (*cleanup) (Portal portal);             /* cleanup hook */
 118         SubTransactionId createSubid;           /* the ID of the creating subxact */
 119
 120         /*
 121          * if createSubid is InvalidSubTransactionId, the portal is held over from
 122          * a previous transaction
 123          */
 124
 125         /* The query or queries the portal will execute */
 126         const char *sourceText;         /* text of query (as of 8.4, never NULL) */
 127         const char *commandTag;         /* command tag for original query */
 128         List       *stmts;                      /* PlannedStmts and/or utility statements */
 129         CachedPlan *cplan;                      /* CachedPlan, if stmts are from one */
 130
 131         ParamListInfo portalParams; /* params to pass to query */
 132
 133         /* Features/options */
 134         PortalStrategy strategy;        /* see above */
 135         int                     cursorOptions;  /* DECLARE CURSOR option bits */
 136
 137         /* Status data */
 138         PortalStatus status;            /* see above */
 139
 140         /* If not NULL, Executor is active; call ExecutorEnd eventually: */
 141         QueryDesc  *queryDesc;          /* info needed for executor invocation */
 142
 143         /* If portal returns tuples, this is their tupdesc: */
 144         TupleDesc       tupDesc;                /* descriptor for result tuples */
 145         /* and these are the format codes to use for the columns: */
 146         int16      *formats;            /* a format code for each column */
 147
 148         /*
 149          * Where we store tuples for a held cursor or a PORTAL_ONE_RETURNING or
 150          * PORTAL_UTIL_SELECT query.  (A cursor held past the end of its
 151          * transaction no longer has any active executor state.)
 152          */
 153         Tuplestorestate *holdStore; /* store for holdable cursors */
 154         MemoryContext holdContext;      /* memory containing holdStore */
 155
 156         /*
 157          * atStart, atEnd and portalPos indicate the current cursor position.
 158          * portalPos is zero before the first row, N after fetching N'th row of
 159          * query.  After we run off the end, portalPos = # of rows in query, and
 160          * atEnd is true.  If portalPos overflows, set posOverflow (this causes us
 161          * to stop relying on its value for navigation).  Note that atStart
 162          * implies portalPos == 0, but not the reverse (portalPos could have
 163          * overflowed).
 164          */
 165         bool            atStart;
 166         bool            atEnd;
 167         bool            posOverflow;
 168         long            portalPos;
 169
 170         /* Presentation data, primarily used by the pg_cursors system view */
 171         TimestampTz creation_time;      /* time at which this portal was defined */
 172         bool            visible;                /* include this portal in pg_cursors? */
 173 } PortalData;
 174
 175 /*
 176  * PortalIsValid
 177  *              True iff portal is valid.
 178  */
 179 #define PortalIsValid(p) PointerIsValid(p)
 180
 181 /*
 182  * Access macros for Portal ... use these in preference to field access.
 183  */
 184 #define PortalGetQueryDesc(portal)      ((portal)->queryDesc)
 185 #define PortalGetHeapMemory(portal) ((portal)->heap)
 186 #define PortalGetPrimaryStmt(portal) PortalListGetPrimaryStmt((portal)->stmts)
 187
 188
 189 /* Prototypes for functions in utils/mmgr/portalmem.c */
 190 extern void EnablePortalManager(void);
 191 extern bool CommitHoldablePortals(void);
 192 extern bool PrepareHoldablePortals(void);
 193 extern void AtCommit_Portals(void);
 194 extern void AtAbort_Portals(void);
 195 extern void AtCleanup_Portals(void);
 196 extern void AtSubCommit_Portals(SubTransactionId mySubid,
 197                                         SubTransactionId parentSubid,
 198                                         ResourceOwner parentXactOwner);
 199 extern void AtSubAbort_Portals(SubTransactionId mySubid,
 200                                    SubTransactionId parentSubid,
 201                                    ResourceOwner parentXactOwner);
 202 extern void AtSubCleanup_Portals(SubTransactionId mySubid);
 203 extern Portal CreatePortal(const char *name, bool allowDup, bool dupSilent);
 204 extern Portal CreateNewPortal(void);
 205 extern void PortalDrop(Portal portal, bool isTopCommit);
 206 extern Portal GetPortalByName(const char *name);
 207 extern void PortalDefineQuery(Portal portal,
 208                                   const char *prepStmtName,
 209                                   const char *sourceText,
 210                                   const char *commandTag,
 211                                   List *stmts,
 212                                   CachedPlan *cplan);
 213 extern Node *PortalListGetPrimaryStmt(List *stmts);
 214 extern void PortalCreateHoldStore(Portal portal);
 215 extern void PortalHashTableDeleteAll(void);
 216
 217 #endif   /* PORTAL_H */