appendinfo.c

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/*-------------------------------------------------------------------------
 *
 * appendinfo.c
 *    Routines for mapping between append parent(s) and children
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/optimizer/path/appendinfo.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "access/table.h"
#include "foreign/fdwapi.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/appendinfo.h"
#include "optimizer/pathnode.h"
#include "parser/parsetree.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/syscache.h"


typedef struct
{
    PlannerInfo *root;
    int         nappinfos;
    AppendRelInfo **appinfos;
} adjust_appendrel_attrs_context;

static void make_inh_translation_list(Relation oldrelation,
                                      Relation newrelation,
                                      Index newvarno,
                                      AppendRelInfo *appinfo);
static Node *adjust_appendrel_attrs_mutator(Node *node,
                                            adjust_appendrel_attrs_context *context);


/*
 * make_append_rel_info
 *    Build an AppendRelInfo for the parent-child pair
 */
AppendRelInfo *
make_append_rel_info(Relation parentrel, Relation childrel,
                     Index parentRTindex, Index childRTindex)
{
    AppendRelInfo *appinfo = makeNode(AppendRelInfo);

    appinfo->parent_relid = parentRTindex;
    appinfo->child_relid = childRTindex;
    appinfo->parent_reltype = parentrel->rd_rel->reltype;
    appinfo->child_reltype = childrel->rd_rel->reltype;
    make_inh_translation_list(parentrel, childrel, childRTindex, appinfo);
    appinfo->parent_reloid = RelationGetRelid(parentrel);

    return appinfo;
}

/*
 * make_inh_translation_list
 *    Build the list of translations from parent Vars to child Vars for
 *    an inheritance child, as well as a reverse-translation array.
 *
 * The reverse-translation array has an entry for each child relation
 * column, which is either the 1-based index of the corresponding parent
 * column, or 0 if there's no match (that happens for dropped child columns,
 * as well as child columns beyond those of the parent, which are allowed in
 * traditional inheritance though not partitioning).
 *
 * For paranoia's sake, we match type/collation as well as attribute name.
 */
static void
make_inh_translation_list(Relation oldrelation, Relation newrelation,
                          Index newvarno,
                          AppendRelInfo *appinfo)
{
    List       *vars = NIL;
    AttrNumber *pcolnos;
    TupleDesc   old_tupdesc = RelationGetDescr(oldrelation);
    TupleDesc   new_tupdesc = RelationGetDescr(newrelation);
    Oid         new_relid = RelationGetRelid(newrelation);
    int         oldnatts = old_tupdesc->natts;
    int         newnatts = new_tupdesc->natts;
    int         old_attno;
    int         new_attno = 0;

    /* Initialize reverse-translation array with all entries zero */
    appinfo->num_child_cols = newnatts;
    appinfo->parent_colnos = pcolnos =
        (AttrNumber *) palloc0(newnatts * sizeof(AttrNumber));

    for (old_attno = 0; old_attno < oldnatts; old_attno++)
    {
        Form_pg_attribute att;
        char       *attname;
        Oid         atttypid;
        int32       atttypmod;
        Oid         attcollation;

        att = TupleDescAttr(old_tupdesc, old_attno);
        if (att->attisdropped)
        {
            /* Just put NULL into this list entry */
            vars = lappend(vars, NULL);
            continue;
        }
        attname = NameStr(att->attname);
        atttypid = att->atttypid;
        atttypmod = att->atttypmod;
        attcollation = att->attcollation;

        /*
         * When we are generating the "translation list" for the parent table
         * of an inheritance set, no need to search for matches.
         */
        if (oldrelation == newrelation)
        {
            vars = lappend(vars, makeVar(newvarno,
                                         (AttrNumber) (old_attno + 1),
                                         atttypid,
                                         atttypmod,
                                         attcollation,
                                         0));
            pcolnos[old_attno] = old_attno + 1;
            continue;
        }

        /*
         * Otherwise we have to search for the matching column by name.
         * There's no guarantee it'll have the same column position, because
         * of cases like ALTER TABLE ADD COLUMN and multiple inheritance.
         * However, in simple cases, the relative order of columns is mostly
         * the same in both relations, so try the column of newrelation that
         * follows immediately after the one that we just found, and if that
         * fails, let syscache handle it.
         */
        if (new_attno >= newnatts ||
            (att = TupleDescAttr(new_tupdesc, new_attno))->attisdropped ||
            strcmp(attname, NameStr(att->attname)) != 0)
        {
            HeapTuple   newtup;

            newtup = SearchSysCacheAttName(new_relid, attname);
            if (!HeapTupleIsValid(newtup))
                elog(ERROR, "could not find inherited attribute \"%s\" of relation \"%s\"",
                     attname, RelationGetRelationName(newrelation));
            new_attno = ((Form_pg_attribute) GETSTRUCT(newtup))->attnum - 1;
            Assert(new_attno >= 0 && new_attno < newnatts);
            ReleaseSysCache(newtup);

            att = TupleDescAttr(new_tupdesc, new_attno);
        }

        /* Found it, check type and collation match */
        if (atttypid != att->atttypid || atttypmod != att->atttypmod)
            elog(ERROR, "attribute \"%s\" of relation \"%s\" does not match parent's type",
                 attname, RelationGetRelationName(newrelation));
        if (attcollation != att->attcollation)
            elog(ERROR, "attribute \"%s\" of relation \"%s\" does not match parent's collation",
                 attname, RelationGetRelationName(newrelation));

        vars = lappend(vars, makeVar(newvarno,
                                     (AttrNumber) (new_attno + 1),
                                     atttypid,
                                     atttypmod,
                                     attcollation,
                                     0));
        pcolnos[new_attno] = old_attno + 1;
        new_attno++;
    }

    appinfo->translated_vars = vars;
}

/*
 * adjust_appendrel_attrs
 *    Copy the specified query or expression and translate Vars referring to a
 *    parent rel to refer to the corresponding child rel instead.  We also
 *    update rtindexes appearing outside Vars, such as resultRelation and
 *    jointree relids.
 *
 * Note: this is only applied after conversion of sublinks to subplans,
 * so we don't need to cope with recursion into sub-queries.
 *
 * Note: this is not hugely different from what pullup_replace_vars() does;
 * maybe we should try to fold the two routines together.
 */
Node *
adjust_appendrel_attrs(PlannerInfo *root, Node *node, int nappinfos,
                       AppendRelInfo **appinfos)
{
    adjust_appendrel_attrs_context context;

    context.root = root;
    context.nappinfos = nappinfos;
    context.appinfos = appinfos;

    /* If there's nothing to adjust, don't call this function. */
    Assert(nappinfos >= 1 && appinfos != NULL);

    /* Should never be translating a Query tree. */
    Assert(node == NULL || !IsA(node, Query));

    return adjust_appendrel_attrs_mutator(node, &context);
}

static Node *
adjust_appendrel_attrs_mutator(Node *node,
                               adjust_appendrel_attrs_context *context)
{
    AppendRelInfo **appinfos = context->appinfos;
    int         nappinfos = context->nappinfos;
    int         cnt;

    if (node == NULL)
        return NULL;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) copyObject(node);
        AppendRelInfo *appinfo = NULL;

        if (var->varlevelsup != 0)
            return (Node *) var;    /* no changes needed */

        for (cnt = 0; cnt < nappinfos; cnt++)
        {
            if (var->varno == appinfos[cnt]->parent_relid)
            {
                appinfo = appinfos[cnt];
                break;
            }
        }

        if (appinfo)
        {
            var->varno = appinfo->child_relid;
            /* it's now a generated Var, so drop any syntactic labeling */
            var->varnosyn = 0;
            var->varattnosyn = 0;
            if (var->varattno > 0)
            {
                Node       *newnode;

                if (var->varattno > list_length(appinfo->translated_vars))
                    elog(ERROR, "attribute %d of relation \"%s\" does not exist",
                         var->varattno, get_rel_name(appinfo->parent_reloid));
                newnode = copyObject(list_nth(appinfo->translated_vars,
                                              var->varattno - 1));
                if (newnode == NULL)
                    elog(ERROR, "attribute %d of relation \"%s\" does not exist",
                         var->varattno, get_rel_name(appinfo->parent_reloid));
                return newnode;
            }
            else if (var->varattno == 0)
            {
                /*
                 * Whole-row Var: if we are dealing with named rowtypes, we
                 * can use a whole-row Var for the child table plus a coercion
                 * step to convert the tuple layout to the parent's rowtype.
                 * Otherwise we have to generate a RowExpr.
                 */
                if (OidIsValid(appinfo->child_reltype))
                {
                    Assert(var->vartype == appinfo->parent_reltype);
                    if (appinfo->parent_reltype != appinfo->child_reltype)
                    {
                        ConvertRowtypeExpr *r = makeNode(ConvertRowtypeExpr);

                        r->arg = (Expr *) var;
                        r->resulttype = appinfo->parent_reltype;
                        r->convertformat = COERCE_IMPLICIT_CAST;
                        r->location = -1;
                        /* Make sure the Var node has the right type ID, too */
                        var->vartype = appinfo->child_reltype;
                        return (Node *) r;
                    }
                }
                else
                {
                    /*
                     * Build a RowExpr containing the translated variables.
                     *
                     * In practice var->vartype will always be RECORDOID here,
                     * so we need to come up with some suitable column names.
                     * We use the parent RTE's column names.
                     *
                     * Note: we can't get here for inheritance cases, so there
                     * is no need to worry that translated_vars might contain
                     * some dummy NULLs.
                     */
                    RowExpr    *rowexpr;
                    List       *fields;
                    RangeTblEntry *rte;

                    rte = rt_fetch(appinfo->parent_relid,
                                   context->root->parse->rtable);
                    fields = copyObject(appinfo->translated_vars);
                    rowexpr = makeNode(RowExpr);
                    rowexpr->args = fields;
                    rowexpr->row_typeid = var->vartype;
                    rowexpr->row_format = COERCE_IMPLICIT_CAST;
                    rowexpr->colnames = copyObject(rte->eref->colnames);
                    rowexpr->location = -1;

                    return (Node *) rowexpr;
                }
            }
            /* system attributes don't need any other translation */
        }
        else if (var->varno == ROWID_VAR)
        {
            /*
             * If it's a ROWID_VAR placeholder, see if we've reached a leaf
             * target rel, for which we can translate the Var to a specific
             * instantiation.  We should never be asked to translate to a set
             * of relids containing more than one leaf target rel, so the
             * answer will be unique.  If we're still considering non-leaf
             * inheritance levels, return the ROWID_VAR Var as-is.
             */
            Relids      leaf_result_relids = context->root->leaf_result_relids;
            Index       leaf_relid = 0;

            for (cnt = 0; cnt < nappinfos; cnt++)
            {
                if (bms_is_member(appinfos[cnt]->child_relid,
                                  leaf_result_relids))
                {
                    if (leaf_relid)
                        elog(ERROR, "cannot translate to multiple leaf relids");
                    leaf_relid = appinfos[cnt]->child_relid;
                }
            }

            if (leaf_relid)
            {
                RowIdentityVarInfo *ridinfo = (RowIdentityVarInfo *)
                list_nth(context->root->row_identity_vars, var->varattno - 1);

                if (bms_is_member(leaf_relid, ridinfo->rowidrels))
                {
                    /* Substitute the Var given in the RowIdentityVarInfo */
                    var = copyObject(ridinfo->rowidvar);
                    /* ... but use the correct relid */
                    var->varno = leaf_relid;
                    /* varnosyn in the RowIdentityVarInfo is probably wrong */
                    var->varnosyn = 0;
                    var->varattnosyn = 0;
                }
                else
                {
                    /*
                     * This leaf rel can't return the desired value, so
                     * substitute a NULL of the correct type.
                     */
                    return (Node *) makeNullConst(var->vartype,
                                                  var->vartypmod,
                                                  var->varcollid);
                }
            }
        }
        return (Node *) var;
    }
    if (IsA(node, CurrentOfExpr))
    {
        CurrentOfExpr *cexpr = (CurrentOfExpr *) copyObject(node);

        for (cnt = 0; cnt < nappinfos; cnt++)
        {
            AppendRelInfo *appinfo = appinfos[cnt];

            if (cexpr->cvarno == appinfo->parent_relid)
            {
                cexpr->cvarno = appinfo->child_relid;
                break;
            }
        }
        return (Node *) cexpr;
    }
    if (IsA(node, PlaceHolderVar))
    {
        /* Copy the PlaceHolderVar node with correct mutation of subnodes */
        PlaceHolderVar *phv;

        phv = (PlaceHolderVar *) expression_tree_mutator(node,
                                                         adjust_appendrel_attrs_mutator,
                                                         (void *) context);
        /* now fix PlaceHolderVar's relid sets */
        if (phv->phlevelsup == 0)
            phv->phrels = adjust_child_relids(phv->phrels, context->nappinfos,
                                              context->appinfos);
        return (Node *) phv;
    }
    /* Shouldn't need to handle planner auxiliary nodes here */
    Assert(!IsA(node, SpecialJoinInfo));
    Assert(!IsA(node, AppendRelInfo));
    Assert(!IsA(node, PlaceHolderInfo));
    Assert(!IsA(node, MinMaxAggInfo));

    /*
     * We have to process RestrictInfo nodes specially.  (Note: although
     * set_append_rel_pathlist will hide RestrictInfos in the parent's
     * baserestrictinfo list from us, it doesn't hide those in joininfo.)
     */
    if (IsA(node, RestrictInfo))
    {
        RestrictInfo *oldinfo = (RestrictInfo *) node;
        RestrictInfo *newinfo = makeNode(RestrictInfo);

        /* Copy all flat-copiable fields */
        memcpy(newinfo, oldinfo, sizeof(RestrictInfo));

        /* Recursively fix the clause itself */
        newinfo->clause = (Expr *)
            adjust_appendrel_attrs_mutator((Node *) oldinfo->clause, context);

        /* and the modified version, if an OR clause */
        newinfo->orclause = (Expr *)
            adjust_appendrel_attrs_mutator((Node *) oldinfo->orclause, context);

        /* adjust relid sets too */
        newinfo->clause_relids = adjust_child_relids(oldinfo->clause_relids,
                                                     context->nappinfos,
                                                     context->appinfos);
        newinfo->required_relids = adjust_child_relids(oldinfo->required_relids,
                                                       context->nappinfos,
                                                       context->appinfos);
        newinfo->outer_relids = adjust_child_relids(oldinfo->outer_relids,
                                                    context->nappinfos,
                                                    context->appinfos);
        newinfo->nullable_relids = adjust_child_relids(oldinfo->nullable_relids,
                                                       context->nappinfos,
                                                       context->appinfos);
        newinfo->left_relids = adjust_child_relids(oldinfo->left_relids,
                                                   context->nappinfos,
                                                   context->appinfos);
        newinfo->right_relids = adjust_child_relids(oldinfo->right_relids,
                                                    context->nappinfos,
                                                    context->appinfos);

        /*
         * Reset cached derivative fields, since these might need to have
         * different values when considering the child relation.  Note we
         * don't reset left_ec/right_ec: each child variable is implicitly
         * equivalent to its parent, so still a member of the same EC if any.
         */
        newinfo->eval_cost.startup = -1;
        newinfo->norm_selec = -1;
        newinfo->outer_selec = -1;
        newinfo->left_em = NULL;
        newinfo->right_em = NULL;
        newinfo->scansel_cache = NIL;
        newinfo->left_bucketsize = -1;
        newinfo->right_bucketsize = -1;
        newinfo->left_mcvfreq = -1;
        newinfo->right_mcvfreq = -1;

        return (Node *) newinfo;
    }

    /*
     * NOTE: we do not need to recurse into sublinks, because they should
     * already have been converted to subplans before we see them.
     */
    Assert(!IsA(node, SubLink));
    Assert(!IsA(node, Query));
    /* We should never see these Query substructures, either. */
    Assert(!IsA(node, RangeTblRef));
    Assert(!IsA(node, JoinExpr));

    return expression_tree_mutator(node, adjust_appendrel_attrs_mutator,
                                   (void *) context);
}

/*
 * adjust_appendrel_attrs_multilevel
 *    Apply Var translations from a toplevel appendrel parent down to a child.
 *
 * In some cases we need to translate expressions referencing a parent relation
 * to reference an appendrel child that's multiple levels removed from it.
 */
Node *
adjust_appendrel_attrs_multilevel(PlannerInfo *root, Node *node,
                                  Relids child_relids,
                                  Relids top_parent_relids)
{
    AppendRelInfo **appinfos;
    Bitmapset  *parent_relids = NULL;
    int         nappinfos;
    int         cnt;

    Assert(bms_num_members(child_relids) == bms_num_members(top_parent_relids));

    appinfos = find_appinfos_by_relids(root, child_relids, &nappinfos);

    /* Construct relids set for the immediate parent of given child. */
    for (cnt = 0; cnt < nappinfos; cnt++)
    {
        AppendRelInfo *appinfo = appinfos[cnt];

        parent_relids = bms_add_member(parent_relids, appinfo->parent_relid);
    }

    /* Recurse if immediate parent is not the top parent. */
    if (!bms_equal(parent_relids, top_parent_relids))
        node = adjust_appendrel_attrs_multilevel(root, node, parent_relids,
                                                 top_parent_relids);

    /* Now translate for this child */
    node = adjust_appendrel_attrs(root, node, nappinfos, appinfos);

    pfree(appinfos);

    return node;
}

/*
 * Substitute child relids for parent relids in a Relid set.  The array of
 * appinfos specifies the substitutions to be performed.
 */
Relids
adjust_child_relids(Relids relids, int nappinfos, AppendRelInfo **appinfos)
{
    Bitmapset  *result = NULL;
    int         cnt;

    for (cnt = 0; cnt < nappinfos; cnt++)
    {
        AppendRelInfo *appinfo = appinfos[cnt];

        /* Remove parent, add child */
        if (bms_is_member(appinfo->parent_relid, relids))
        {
            /* Make a copy if we are changing the set. */
            if (!result)
                result = bms_copy(relids);

            result = bms_del_member(result, appinfo->parent_relid);
            result = bms_add_member(result, appinfo->child_relid);
        }
    }

    /* If we made any changes, return the modified copy. */
    if (result)
        return result;

    /* Otherwise, return the original set without modification. */
    return relids;
}

/*
 * Replace any relid present in top_parent_relids with its child in
 * child_relids. Members of child_relids can be multiple levels below top
 * parent in the partition hierarchy.
 */
Relids
adjust_child_relids_multilevel(PlannerInfo *root, Relids relids,
                               Relids child_relids, Relids top_parent_relids)
{
    AppendRelInfo **appinfos;
    int         nappinfos;
    Relids      parent_relids = NULL;
    Relids      result;
    Relids      tmp_result = NULL;
    int         cnt;

    /*
     * If the given relids set doesn't contain any of the top parent relids,
     * it will remain unchanged.
     */
    if (!bms_overlap(relids, top_parent_relids))
        return relids;

    appinfos = find_appinfos_by_relids(root, child_relids, &nappinfos);

    /* Construct relids set for the immediate parent of the given child. */
    for (cnt = 0; cnt < nappinfos; cnt++)
    {
        AppendRelInfo *appinfo = appinfos[cnt];

        parent_relids = bms_add_member(parent_relids, appinfo->parent_relid);
    }

    /* Recurse if immediate parent is not the top parent. */
    if (!bms_equal(parent_relids, top_parent_relids))
    {
        tmp_result = adjust_child_relids_multilevel(root, relids,
                                                    parent_relids,
                                                    top_parent_relids);
        relids = tmp_result;
    }

    result = adjust_child_relids(relids, nappinfos, appinfos);

    /* Free memory consumed by any intermediate result. */
    if (tmp_result)
        bms_free(tmp_result);
    bms_free(parent_relids);
    pfree(appinfos);

    return result;
}

/*
 * adjust_inherited_attnums
 *    Translate an integer list of attribute numbers from parent to child.
 */
List *
adjust_inherited_attnums(List *attnums, AppendRelInfo *context)
{
    List       *result = NIL;
    ListCell   *lc;

    /* This should only happen for an inheritance case, not UNION ALL */
    Assert(OidIsValid(context->parent_reloid));

    /* Look up each attribute in the AppendRelInfo's translated_vars list */
    foreach(lc, attnums)
    {
        AttrNumber  parentattno = lfirst_int(lc);
        Var        *childvar;

        /* Look up the translation of this column: it must be a Var */
        if (parentattno <= 0 ||
            parentattno > list_length(context->translated_vars))
            elog(ERROR, "attribute %d of relation \"%s\" does not exist",
                 parentattno, get_rel_name(context->parent_reloid));
        childvar = (Var *) list_nth(context->translated_vars, parentattno - 1);
        if (childvar == NULL || !IsA(childvar, Var))
            elog(ERROR, "attribute %d of relation \"%s\" does not exist",
                 parentattno, get_rel_name(context->parent_reloid));

        result = lappend_int(result, childvar->varattno);
    }
    return result;
}

/*
 * adjust_inherited_attnums_multilevel
 *    As above, but traverse multiple inheritance levels as needed.
 */
List *
adjust_inherited_attnums_multilevel(PlannerInfo *root, List *attnums,
                                    Index child_relid, Index top_parent_relid)
{
    AppendRelInfo *appinfo = root->append_rel_array[child_relid];

    if (!appinfo)
        elog(ERROR, "child rel %d not found in append_rel_array", child_relid);

    /* Recurse if immediate parent is not the top parent. */
    if (appinfo->parent_relid != top_parent_relid)
        attnums = adjust_inherited_attnums_multilevel(root, attnums,
                                                      appinfo->parent_relid,
                                                      top_parent_relid);

    /* Now translate for this child */
    return adjust_inherited_attnums(attnums, appinfo);
}

/*
 * get_translated_update_targetlist
 *    Get the processed_tlist of an UPDATE query, translated as needed to
 *    match a child target relation.
 *
 * Optionally also return the list of target column numbers translated
 * to this target relation.  (The resnos in processed_tlist MUST NOT be
 * relied on for this purpose.)
 */
void
get_translated_update_targetlist(PlannerInfo *root, Index relid,
                                 List **processed_tlist, List **update_colnos)
{
    /* This is pretty meaningless for commands other than UPDATE. */
    Assert(root->parse->commandType == CMD_UPDATE);
    if (relid == root->parse->resultRelation)
    {
        /*
         * Non-inheritance case, so it's easy.  The caller might be expecting
         * a tree it can scribble on, though, so copy.
         */
        *processed_tlist = copyObject(root->processed_tlist);
        if (update_colnos)
            *update_colnos = copyObject(root->update_colnos);
    }
    else
    {
        Assert(bms_is_member(relid, root->all_result_relids));
        *processed_tlist = (List *)
            adjust_appendrel_attrs_multilevel(root,
                                              (Node *) root->processed_tlist,
                                              bms_make_singleton(relid),
                                              bms_make_singleton(root->parse->resultRelation));
        if (update_colnos)
            *update_colnos =
                adjust_inherited_attnums_multilevel(root, root->update_colnos,
                                                    relid,
                                                    root->parse->resultRelation);
    }
}

/*
 * find_appinfos_by_relids
 *      Find AppendRelInfo structures for all relations specified by relids.
 *
 * The AppendRelInfos are returned in an array, which can be pfree'd by the
 * caller. *nappinfos is set to the number of entries in the array.
 */
AppendRelInfo **
find_appinfos_by_relids(PlannerInfo *root, Relids relids, int *nappinfos)
{
    AppendRelInfo **appinfos;
    int         cnt = 0;
    int         i;

    *nappinfos = bms_num_members(relids);
    appinfos = (AppendRelInfo **) palloc(sizeof(AppendRelInfo *) * *nappinfos);

    i = -1;
    while ((i = bms_next_member(relids, i)) >= 0)
    {
        AppendRelInfo *appinfo = root->append_rel_array[i];

        if (!appinfo)
            elog(ERROR, "child rel %d not found in append_rel_array", i);

        appinfos[cnt++] = appinfo;
    }
    return appinfos;
}


/*****************************************************************************
 *
 *      ROW-IDENTITY VARIABLE MANAGEMENT
 *
 * This code lacks a good home, perhaps.  We choose to keep it here because
 * adjust_appendrel_attrs_mutator() is its principal co-conspirator.  That
 * function does most of what is needed to expand ROWID_VAR Vars into the
 * right things.
 *
 *****************************************************************************/

/*
 * add_row_identity_var
 *    Register a row-identity column to be used in UPDATE/DELETE.
 *
 * The Var must be equal(), aside from varno, to any other row-identity
 * column with the same rowid_name.  Thus, for example, "wholerow"
 * row identities had better use vartype == RECORDOID.
 *
 * rtindex is currently redundant with rowid_var->varno, but we specify
 * it as a separate parameter in case this is ever generalized to support
 * non-Var expressions.  (We could reasonably handle expressions over
 * Vars of the specified rtindex, but for now that seems unnecessary.)
 */
void
add_row_identity_var(PlannerInfo *root, Var *orig_var,
                     Index rtindex, const char *rowid_name)
{
    TargetEntry *tle;
    Var        *rowid_var;
    RowIdentityVarInfo *ridinfo;
    ListCell   *lc;

    /* For now, the argument must be just a Var of the given rtindex */
    Assert(IsA(orig_var, Var));
    Assert(orig_var->varno == rtindex);
    Assert(orig_var->varlevelsup == 0);

    /*
     * If we're doing non-inherited UPDATE/DELETE, there's little need for
     * ROWID_VAR shenanigans.  Just shove the presented Var into the
     * processed_tlist, and we're done.
     */
    if (rtindex == root->parse->resultRelation)
    {
        tle = makeTargetEntry((Expr *) orig_var,
                              list_length(root->processed_tlist) + 1,
                              pstrdup(rowid_name),
                              true);
        root->processed_tlist = lappend(root->processed_tlist, tle);
        return;
    }

    /*
     * Otherwise, rtindex should reference a leaf target relation that's being
     * added to the query during expand_inherited_rtentry().
     */
    Assert(bms_is_member(rtindex, root->leaf_result_relids));
    Assert(root->append_rel_array[rtindex] != NULL);

    /*
     * We have to find a matching RowIdentityVarInfo, or make one if there is
     * none.  To allow using equal() to match the vars, change the varno to
     * ROWID_VAR, leaving all else alone.
     */
    rowid_var = copyObject(orig_var);
    /* This could eventually become ChangeVarNodes() */
    rowid_var->varno = ROWID_VAR;

    /* Look for an existing row-id column of the same name */
    foreach(lc, root->row_identity_vars)
    {
        ridinfo = (RowIdentityVarInfo *) lfirst(lc);
        if (strcmp(rowid_name, ridinfo->rowidname) != 0)
            continue;
        if (equal(rowid_var, ridinfo->rowidvar))
        {
            /* Found a match; we need only record that rtindex needs it too */
            ridinfo->rowidrels = bms_add_member(ridinfo->rowidrels, rtindex);
            return;
        }
        else
        {
            /* Ooops, can't handle this */
            elog(ERROR, "conflicting uses of row-identity name \"%s\"",
                 rowid_name);
        }
    }

    /* No request yet, so add a new RowIdentityVarInfo */
    ridinfo = makeNode(RowIdentityVarInfo);
    ridinfo->rowidvar = copyObject(rowid_var);
    /* for the moment, estimate width using just the datatype info */
    ridinfo->rowidwidth = get_typavgwidth(exprType((Node *) rowid_var),
                                          exprTypmod((Node *) rowid_var));
    ridinfo->rowidname = pstrdup(rowid_name);
    ridinfo->rowidrels = bms_make_singleton(rtindex);

    root->row_identity_vars = lappend(root->row_identity_vars, ridinfo);

    /* Change rowid_var into a reference to this row_identity_vars entry */
    rowid_var->varattno = list_length(root->row_identity_vars);

    /* Push the ROWID_VAR reference variable into processed_tlist */
    tle = makeTargetEntry((Expr *) rowid_var,
                          list_length(root->processed_tlist) + 1,
                          pstrdup(rowid_name),
                          true);
    root->processed_tlist = lappend(root->processed_tlist, tle);
}

/*
 * add_row_identity_columns
 *
 * This function adds the row identity columns needed by the core code.
 * FDWs might call add_row_identity_var() for themselves to add nonstandard
 * columns.  (Duplicate requests are fine.)
 */
void
add_row_identity_columns(PlannerInfo *root, Index rtindex,
                         RangeTblEntry *target_rte,
                         Relation target_relation)
{
    CmdType     commandType = root->parse->commandType;
    char        relkind = target_relation->rd_rel->relkind;
    Var        *var;

    Assert(commandType == CMD_UPDATE || commandType == CMD_DELETE);

    if (relkind == RELKIND_RELATION ||
        relkind == RELKIND_MATVIEW ||
        relkind == RELKIND_PARTITIONED_TABLE)
    {
        /*
         * Emit CTID so that executor can find the row to update or delete.
         */
        var = makeVar(rtindex,
                      SelfItemPointerAttributeNumber,
                      TIDOID,
                      -1,
                      InvalidOid,
                      0);
        add_row_identity_var(root, var, rtindex, "ctid");
    }
    else if (relkind == RELKIND_FOREIGN_TABLE)
    {
        /*
         * Let the foreign table's FDW add whatever junk TLEs it wants.
         */
        FdwRoutine *fdwroutine;

        fdwroutine = GetFdwRoutineForRelation(target_relation, false);

        if (fdwroutine->AddForeignUpdateTargets != NULL)
            fdwroutine->AddForeignUpdateTargets(root, rtindex,
                                                target_rte, target_relation);

        /*
         * For UPDATE, we need to make the FDW fetch unchanged columns by
         * asking it to fetch a whole-row Var.  That's because the top-level
         * targetlist only contains entries for changed columns, but
         * ExecUpdate will need to build the complete new tuple.  (Actually,
         * we only really need this in UPDATEs that are not pushed to the
         * remote side, but it's hard to tell if that will be the case at the
         * point when this function is called.)
         *
         * We will also need the whole row if there are any row triggers, so
         * that the executor will have the "old" row to pass to the trigger.
         * Alas, this misses system columns.
         */
        if (commandType == CMD_UPDATE ||
            (target_relation->trigdesc &&
             (target_relation->trigdesc->trig_delete_after_row ||
              target_relation->trigdesc->trig_delete_before_row)))
        {
            var = makeVar(rtindex,
                          InvalidAttrNumber,
                          RECORDOID,
                          -1,
                          InvalidOid,
                          0);
            add_row_identity_var(root, var, rtindex, "wholerow");
        }
    }
}

/*
 * distribute_row_identity_vars
 *
 * After we have finished identifying all the row identity columns
 * needed by an inherited UPDATE/DELETE query, make sure that these
 * columns will be generated by all the target relations.
 *
 * This is more or less like what build_base_rel_tlists() does,
 * except that it would not understand what to do with ROWID_VAR Vars.
 * Since that function runs before inheritance relations are expanded,
 * it will never see any such Vars anyway.
 */
void
distribute_row_identity_vars(PlannerInfo *root)
{
    Query      *parse = root->parse;
    int         result_relation = parse->resultRelation;
    RangeTblEntry *target_rte;
    RelOptInfo *target_rel;
    ListCell   *lc;

    /* There's nothing to do if this isn't an inherited UPDATE/DELETE. */
    if (parse->commandType != CMD_UPDATE && parse->commandType != CMD_DELETE)
    {
        Assert(root->row_identity_vars == NIL);
        return;
    }
    target_rte = rt_fetch(result_relation, parse->rtable);
    if (!target_rte->inh)
    {
        Assert(root->row_identity_vars == NIL);
        return;
    }

    /*
     * Ordinarily, we expect that leaf result relation(s) will have added some
     * ROWID_VAR Vars to the query.  However, it's possible that constraint
     * exclusion suppressed every leaf relation.  The executor will get upset
     * if the plan has no row identity columns at all, even though it will
     * certainly process no rows.  Handle this edge case by re-opening the top
     * result relation and adding the row identity columns it would have used,
     * as preprocess_targetlist() would have done if it weren't marked "inh".
     * (This is a bit ugly, but it seems better to confine the ugliness and
     * extra cycles to this unusual corner case.)  We needn't worry about
     * fixing the rel's reltarget, as that won't affect the finished plan.
     */
    if (root->row_identity_vars == NIL)
    {
        Relation    target_relation;

        target_relation = table_open(target_rte->relid, NoLock);
        add_row_identity_columns(root, result_relation,
                                 target_rte, target_relation);
        table_close(target_relation, NoLock);
        return;
    }

    /*
     * Dig through the processed_tlist to find the ROWID_VAR reference Vars,
     * and forcibly copy them into the reltarget list of the topmost target
     * relation.  That's sufficient because they'll be copied to the
     * individual leaf target rels (with appropriate translation) later,
     * during appendrel expansion --- see set_append_rel_size().
     */
    target_rel = find_base_rel(root, result_relation);

    foreach(lc, root->processed_tlist)
    {
        TargetEntry *tle = lfirst(lc);
        Var        *var = (Var *) tle->expr;

        if (var && IsA(var, Var) && var->varno == ROWID_VAR)
        {
            target_rel->reltarget->exprs =
                lappend(target_rel->reltarget->exprs, copyObject(var));
            /* reltarget cost and width will be computed later */
        }
    }
}