TLA  Line data    Source code

       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) 1996-2023, 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 CBC         267 : create_queryEnv(void)
      40                 : {
      41             267 :     return (QueryEnvironment *) palloc0(sizeof(QueryEnvironment));
      42                 : }
      43                 : 
      44                 : EphemeralNamedRelationMetadata
      45          250378 : get_visible_ENR_metadata(QueryEnvironment *queryEnv, const char *refname)
      46                 : {
      47                 :     EphemeralNamedRelation enr;
      48                 : 
      49          250378 :     Assert(refname != NULL);
      50                 : 
      51          250378 :     if (queryEnv == NULL)
      52          249910 :         return NULL;
      53                 : 
      54             468 :     enr = get_ENR(queryEnv, refname);
      55                 : 
      56             468 :     if (enr)
      57             447 :         return &(enr->md);
      58                 : 
      59              21 :     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             342 : register_ENR(QueryEnvironment *queryEnv, EphemeralNamedRelation enr)
      70                 : {
      71             342 :     Assert(enr != NULL);
      72             342 :     Assert(get_ENR(queryEnv, enr->md.name) == NULL);
      73                 : 
      74             342 :     queryEnv->namedRelList = lappend(queryEnv->namedRelList, enr);
      75             342 : }
      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 UBC           0 : unregister_ENR(QueryEnvironment *queryEnv, const char *name)
      83                 : {
      84                 :     EphemeralNamedRelation match;
      85                 : 
      86               0 :     match = get_ENR(queryEnv, name);
      87               0 :     if (match)
      88               0 :         queryEnv->namedRelList = list_delete(queryEnv->namedRelList, match);
      89               0 : }
      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 CBC        1215 : get_ENR(QueryEnvironment *queryEnv, const char *name)
      97                 : {
      98                 :     ListCell   *lc;
      99                 : 
     100            1215 :     Assert(name != NULL);
     101                 : 
     102            1215 :     if (queryEnv == NULL)
     103 UBC           0 :         return NULL;
     104                 : 
     105 CBC        1557 :     foreach(lc, queryEnv->namedRelList)
     106                 :     {
     107            1119 :         EphemeralNamedRelation enr = (EphemeralNamedRelation) lfirst(lc);
     108                 : 
     109            1119 :         if (strcmp(enr->md.name, name) == 0)
     110             777 :             return enr;
     111                 :     }
     112                 : 
     113             438 :     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             552 : ENRMetadataGetTupDesc(EphemeralNamedRelationMetadata enrmd)
     126                 : {
     127                 :     TupleDesc   tupdesc;
     128                 : 
     129                 :     /* One, and only one, of these fields must be filled. */
     130             552 :     Assert((enrmd->reliddesc == InvalidOid) != (enrmd->tupdesc == NULL));
     131                 : 
     132             552 :     if (enrmd->tupdesc != NULL)
     133 UBC           0 :         tupdesc = enrmd->tupdesc;
     134                 :     else
     135                 :     {
     136                 :         Relation    relation;
     137                 : 
     138 CBC         552 :         relation = table_open(enrmd->reliddesc, NoLock);
     139             552 :         tupdesc = relation->rd_att;
     140             552 :         table_close(relation, NoLock);
     141                 :     }
     142                 : 
     143             552 :     return tupdesc;
     144                 : }