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) 1996-2024, 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         534 : create_queryEnv(void)
      40             : {
      41         534 :     return (QueryEnvironment *) palloc0(sizeof(QueryEnvironment));
      42             : }
      43             : 
      44             : EphemeralNamedRelationMetadata
      45      258990 : get_visible_ENR_metadata(QueryEnvironment *queryEnv, const char *refname)
      46             : {
      47             :     EphemeralNamedRelation enr;
      48             : 
      49             :     Assert(refname != NULL);
      50             : 
      51      258990 :     if (queryEnv == NULL)
      52      258038 :         return NULL;
      53             : 
      54         952 :     enr = get_ENR(queryEnv, refname);
      55             : 
      56         952 :     if (enr)
      57         910 :         return &(enr->md);
      58             : 
      59          42 :     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         684 : register_ENR(QueryEnvironment *queryEnv, EphemeralNamedRelation enr)
      70             : {
      71             :     Assert(enr != NULL);
      72             :     Assert(get_ENR(queryEnv, enr->md.name) == NULL);
      73             : 
      74         684 :     queryEnv->namedRelList = lappend(queryEnv->namedRelList, enr);
      75         684 : }
      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           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        1762 : get_ENR(QueryEnvironment *queryEnv, const char *name)
      97             : {
      98             :     ListCell   *lc;
      99             : 
     100             :     Assert(name != NULL);
     101             : 
     102        1762 :     if (queryEnv == NULL)
     103           0 :         return NULL;
     104             : 
     105        2304 :     foreach(lc, queryEnv->namedRelList)
     106             :     {
     107        2112 :         EphemeralNamedRelation enr = (EphemeralNamedRelation) lfirst(lc);
     108             : 
     109        2112 :         if (strcmp(enr->md.name, name) == 0)
     110        1570 :             return enr;
     111             :     }
     112             : 
     113         192 :     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        1112 : 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        1112 :     if (enrmd->tupdesc != NULL)
     133           0 :         tupdesc = enrmd->tupdesc;
     134             :     else
     135             :     {
     136             :         Relation    relation;
     137             : 
     138        1112 :         relation = table_open(enrmd->reliddesc, NoLock);
     139        1112 :         tupdesc = relation->rd_att;
     140        1112 :         table_close(relation, NoLock);
     141             :     }
     142             : 
     143        1112 :     return tupdesc;
     144             : }