src/backend/optimizer/path/tidpath.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * tidpath.c
   4  *        Routines to determine which TID conditions are usable for scanning
   5  *        a given relation, and create TidPaths accordingly.
   6  *
   7  * What we are looking for here is WHERE conditions of the form
   8  * "CTID = pseudoconstant", which can be implemented by just fetching
   9  * the tuple directly via heap_fetch().  We can also handle OR'd conditions
  10  * such as (CTID = const1) OR (CTID = const2), as well as ScalarArrayOpExpr
  11  * conditions of the form CTID = ANY(pseudoconstant_array).  In particular
  12  * this allows
  13  *              WHERE ctid IN (tid1, tid2, ...)
  14  *
  15  * We also support "WHERE CURRENT OF cursor" conditions (CurrentOfExpr),
  16  * which amount to "CTID = run-time-determined-TID".  These could in
  17  * theory be translated to a simple comparison of CTID to the result of
  18  * a function, but in practice it works better to keep the special node
  19  * representation all the way through to execution.
  20  *
  21  * There is currently no special support for joins involving CTID; in
  22  * particular nothing corresponding to best_inner_indexscan().  Since it's
  23  * not very useful to store TIDs of one table in another table, there
  24  * doesn't seem to be enough use-case to justify adding a lot of code
  25  * for that.
  26  *
  27  *
  28  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  29  * Portions Copyright (c) 1994, Regents of the University of California
  30  *
  31  *
  32  * IDENTIFICATION
  33  *        $PostgreSQL$
  34  *
  35  *-------------------------------------------------------------------------
  36  */
  37 #include "postgres.h"
  38
  39 #include "access/sysattr.h"
  40 #include "catalog/pg_operator.h"
  41 #include "catalog/pg_type.h"
  42 #include "nodes/nodeFuncs.h"
  43 #include "optimizer/clauses.h"
  44 #include "optimizer/pathnode.h"
  45 #include "optimizer/paths.h"
  46
  47
  48 static bool IsTidEqualClause(OpExpr *node, int varno);
  49 static bool IsTidEqualAnyClause(ScalarArrayOpExpr *node, int varno);
  50 static List *TidQualFromExpr(Node *expr, int varno);
  51 static List *TidQualFromRestrictinfo(List *restrictinfo, int varno);
  52
  53
  54 /*
  55  * Check to see if an opclause is of the form
  56  *              CTID = pseudoconstant
  57  * or
  58  *              pseudoconstant = CTID
  59  *
  60  * We check that the CTID Var belongs to relation "varno".      That is probably
  61  * redundant considering this is only applied to restriction clauses, but
  62  * let's be safe.
  63  */
  64 static bool
  65 IsTidEqualClause(OpExpr *node, int varno)
  66 {
  67         Node       *arg1,
  68                            *arg2,
  69                            *other;
  70         Var                *var;
  71
  72         /* Operator must be tideq */
  73         if (node->opno != TIDEqualOperator)
  74                 return false;
  75         if (list_length(node->args) != 2)
  76                 return false;
  77         arg1 = linitial(node->args);
  78         arg2 = lsecond(node->args);
  79
  80         /* Look for CTID as either argument */
  81         other = NULL;
  82         if (arg1 && IsA(arg1, Var))
  83         {
  84                 var = (Var *) arg1;
  85                 if (var->varattno == SelfItemPointerAttributeNumber &&
  86                         var->vartype == TIDOID &&
  87                         var->varno == varno &&
  88                         var->varlevelsup == 0)
  89                         other = arg2;
  90         }
  91         if (!other && arg2 && IsA(arg2, Var))
  92         {
  93                 var = (Var *) arg2;
  94                 if (var->varattno == SelfItemPointerAttributeNumber &&
  95                         var->vartype == TIDOID &&
  96                         var->varno == varno &&
  97                         var->varlevelsup == 0)
  98                         other = arg1;
  99         }
 100         if (!other)
 101                 return false;
 102         if (exprType(other) != TIDOID)
 103                 return false;                   /* probably can't happen */
 104
 105         /* The other argument must be a pseudoconstant */
 106         if (!is_pseudo_constant_clause(other))
 107                 return false;
 108
 109         return true;                            /* success */
 110 }
 111
 112 /*
 113  * Check to see if a clause is of the form
 114  *              CTID = ANY (pseudoconstant_array)
 115  */
 116 static bool
 117 IsTidEqualAnyClause(ScalarArrayOpExpr *node, int varno)
 118 {
 119         Node       *arg1,
 120                            *arg2;
 121
 122         /* Operator must be tideq */
 123         if (node->opno != TIDEqualOperator)
 124                 return false;
 125         if (!node->useOr)
 126                 return false;
 127         Assert(list_length(node->args) == 2);
 128         arg1 = linitial(node->args);
 129         arg2 = lsecond(node->args);
 130
 131         /* CTID must be first argument */
 132         if (arg1 && IsA(arg1, Var))
 133         {
 134                 Var                *var = (Var *) arg1;
 135
 136                 if (var->varattno == SelfItemPointerAttributeNumber &&
 137                         var->vartype == TIDOID &&
 138                         var->varno == varno &&
 139                         var->varlevelsup == 0)
 140                 {
 141                         /* The other argument must be a pseudoconstant */
 142                         if (is_pseudo_constant_clause(arg2))
 143                                 return true;    /* success */
 144                 }
 145         }
 146
 147         return false;
 148 }
 149
 150 /*
 151  *      Extract a set of CTID conditions from the given qual expression
 152  *
 153  *      Returns a List of CTID qual expressions (with implicit OR semantics
 154  *      across the list), or NIL if there are no usable conditions.
 155  *
 156  *      If the expression is an AND clause, we can use a CTID condition
 157  *      from any sub-clause.  If it is an OR clause, we must be able to
 158  *      extract a CTID condition from every sub-clause, or we can't use it.
 159  *
 160  *      In theory, in the AND case we could get CTID conditions from different
 161  *      sub-clauses, in which case we could try to pick the most efficient one.
 162  *      In practice, such usage seems very unlikely, so we don't bother; we
 163  *      just exit as soon as we find the first candidate.
 164  */
 165 static List *
 166 TidQualFromExpr(Node *expr, int varno)
 167 {
 168         List       *rlst = NIL;
 169         ListCell   *l;
 170
 171         if (is_opclause(expr))
 172         {
 173                 /* base case: check for tideq opclause */
 174                 if (IsTidEqualClause((OpExpr *) expr, varno))
 175                         rlst = list_make1(expr);
 176         }
 177         else if (expr && IsA(expr, ScalarArrayOpExpr))
 178         {
 179                 /* another base case: check for tid = ANY clause */
 180                 if (IsTidEqualAnyClause((ScalarArrayOpExpr *) expr, varno))
 181                         rlst = list_make1(expr);
 182         }
 183         else if (expr && IsA(expr, CurrentOfExpr))
 184         {
 185                 /* another base case: check for CURRENT OF on this rel */
 186                 if (((CurrentOfExpr *) expr)->cvarno == varno)
 187                         rlst = list_make1(expr);
 188         }
 189         else if (and_clause(expr))
 190         {
 191                 foreach(l, ((BoolExpr *) expr)->args)
 192                 {
 193                         rlst = TidQualFromExpr((Node *) lfirst(l), varno);
 194                         if (rlst)
 195                                 break;
 196                 }
 197         }
 198         else if (or_clause(expr))
 199         {
 200                 foreach(l, ((BoolExpr *) expr)->args)
 201                 {
 202                         List       *frtn = TidQualFromExpr((Node *) lfirst(l), varno);
 203
 204                         if (frtn)
 205                                 rlst = list_concat(rlst, frtn);
 206                         else
 207                         {
 208                                 if (rlst)
 209                                         list_free(rlst);
 210                                 rlst = NIL;
 211                                 break;
 212                         }
 213                 }
 214         }
 215         return rlst;
 216 }
 217
 218 /*
 219  *      Extract a set of CTID conditions from the given restrictinfo list
 220  *
 221  *      This is essentially identical to the AND case of TidQualFromExpr,
 222  *      except for the format of the input.
 223  */
 224 static List *
 225 TidQualFromRestrictinfo(List *restrictinfo, int varno)
 226 {
 227         List       *rlst = NIL;
 228         ListCell   *l;
 229
 230         foreach(l, restrictinfo)
 231         {
 232                 RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
 233
 234                 if (!IsA(rinfo, RestrictInfo))
 235                         continue;                       /* probably should never happen */
 236                 rlst = TidQualFromExpr((Node *) rinfo->clause, varno);
 237                 if (rlst)
 238                         break;
 239         }
 240         return rlst;
 241 }
 242
 243 /*
 244  * create_tidscan_paths
 245  *        Create paths corresponding to direct TID scans of the given rel.
 246  *
 247  *        Candidate paths are added to the rel's pathlist (using add_path).
 248  */
 249 void
 250 create_tidscan_paths(PlannerInfo *root, RelOptInfo *rel)
 251 {
 252         List       *tidquals;
 253
 254         tidquals = TidQualFromRestrictinfo(rel->baserestrictinfo, rel->relid);
 255
 256         if (tidquals)
 257                 add_path(rel, (Path *) create_tidscan_path(root, rel, tidquals));
 258 }