src/backend/utils/misc/queryenvironment.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * queryenvironment.c
   4  *        Query environment, to store context-specific values like ephemeral named
   5  *        relations.  Initial use is for named tuplestores for delta information
   6  *        from "normal" relations.
   7  *
   8  * The initial implementation uses a list because the number of such relations
   9  * in any one context is expected to be very small.  If that becomes a
  10  * performance problem, the implementation can be changed with no other impact
  11  * on callers, since this is an opaque structure.  This is the reason to
  12  * require a create function.
  13  *
  14  * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
  15  * Portions Copyright (c) 1994, Regents of the University of California
  16  *
  17  *
  18  * IDENTIFICATION
  19  *        src/backend/utils/misc/queryenvironment.c
  20  *
  21  *-------------------------------------------------------------------------
  22  */
  23 #include "postgres.h"
  24
  25 #include "access/table.h"
  26 #include "utils/queryenvironment.h"
  27 #include "utils/rel.h"
  28
  29 /*
  30  * Private state of a query environment.
  31  */
  32 struct QueryEnvironment
  33 {
  34         List       *namedRelList;
  35 };
  36
  37
  38 QueryEnvironment *
  39 create_queryEnv(void)
  40 {
  41         return (QueryEnvironment *) palloc0(sizeof(QueryEnvironment));
  42 }
  43
  44 EphemeralNamedRelationMetadata
  45 get_visible_ENR_metadata(QueryEnvironment *queryEnv, const char *refname)
  46 {
  47         EphemeralNamedRelation enr;
  48
  49         Assert(refname != NULL);
  50
  51         if (queryEnv == NULL)
  52                 return NULL;
  53
  54         enr = get_ENR(queryEnv, refname);
  55
  56         if (enr)
  57                 return &(enr->md);
  58
  59         return NULL;
  60 }
  61
  62 /*
  63  * Register a named relation for use in the given environment.
  64  *
  65  * If this is intended exclusively for planning purposes, the tstate field can
  66  * be left NULL;
  67  */
  68 void
  69 register_ENR(QueryEnvironment *queryEnv, EphemeralNamedRelation enr)
  70 {
  71         Assert(enr != NULL);
  72         Assert(get_ENR(queryEnv, enr->md.name) == NULL);
  73
  74         queryEnv->namedRelList = lappend(queryEnv->namedRelList, enr);
  75 }
  76
  77 /*
  78  * Unregister an ephemeral relation by name.  This will probably be a rarely
  79  * used function, but seems like it should be provided "just in case".
  80  */
  81 void
  82 unregister_ENR(QueryEnvironment *queryEnv, const char *name)
  83 {
  84         EphemeralNamedRelation match;
  85
  86         match = get_ENR(queryEnv, name);
  87         if (match)
  88                 queryEnv->namedRelList = list_delete(queryEnv->namedRelList, match);
  89 }
  90
  91 /*
  92  * This returns an ENR if there is a name match in the given collection.  It
  93  * must quietly return NULL if no match is found.
  94  */
  95 EphemeralNamedRelation
  96 get_ENR(QueryEnvironment *queryEnv, const char *name)
  97 {
  98         ListCell   *lc;
  99
 100         Assert(name != NULL);
 101
 102         if (queryEnv == NULL)
 103                 return NULL;
 104
 105         foreach(lc, queryEnv->namedRelList)
 106         {
 107                 EphemeralNamedRelation enr = (EphemeralNamedRelation) lfirst(lc);
 108
 109                 if (strcmp(enr->md.name, name) == 0)
 110                         return enr;
 111         }
 112
 113         return NULL;
 114 }
 115
 116 /*
 117  * Gets the TupleDesc for a Ephemeral Named Relation, based on which field was
 118  * filled.
 119  *
 120  * When the TupleDesc is based on a relation from the catalogs, we count on
 121  * that relation being used at the same time, so that appropriate locks will
 122  * already be held.  Locking here would be too late anyway.
 123  */
 124 TupleDesc
 125 ENRMetadataGetTupDesc(EphemeralNamedRelationMetadata enrmd)
 126 {
 127         TupleDesc       tupdesc;
 128
 129         /* One, and only one, of these fields must be filled. */
 130         Assert((enrmd->reliddesc == InvalidOid) != (enrmd->tupdesc == NULL));
 131
 132         if (enrmd->tupdesc != NULL)
 133                 tupdesc = enrmd->tupdesc;
 134         else
 135         {
 136                 Relation        relation;
 137
 138                 relation = table_open(enrmd->reliddesc, NoLock);
 139                 tupdesc = relation->rd_att;
 140                 table_close(relation, NoLock);
 141         }
 142
 143         return tupdesc;
 144 }