PostgreSQL Source Code  git master
 All Data Structures Namespaces Files Functions Variables Typedefs Enumerations Enumerator Macros
placeholder.c
Go to the documentation of this file.
1 /*-------------------------------------------------------------------------
2  *
3  * placeholder.c
4  * PlaceHolderVar and PlaceHolderInfo manipulation routines
5  *
6  *
7  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
8  * Portions Copyright (c) 1994, Regents of the University of California
9  *
10  *
11  * IDENTIFICATION
12  * src/backend/optimizer/util/placeholder.c
13  *
14  *-------------------------------------------------------------------------
15  */
16 #include "postgres.h"
17 
18 #include "nodes/nodeFuncs.h"
19 #include "optimizer/cost.h"
20 #include "optimizer/pathnode.h"
21 #include "optimizer/placeholder.h"
22 #include "optimizer/planmain.h"
23 #include "optimizer/var.h"
24 #include "utils/lsyscache.h"
25 
26 /* Local functions */
27 static void find_placeholders_recurse(PlannerInfo *root, Node *jtnode);
28 static void find_placeholders_in_expr(PlannerInfo *root, Node *expr);
29 
30 
31 /*
32  * make_placeholder_expr
33  * Make a PlaceHolderVar for the given expression.
34  *
35  * phrels is the syntactic location (as a set of baserels) to attribute
36  * to the expression.
37  */
40 {
42 
43  phv->phexpr = expr;
44  phv->phrels = phrels;
45  phv->phid = ++(root->glob->lastPHId);
46  phv->phlevelsup = 0;
47 
48  return phv;
49 }
50 
51 /*
52  * find_placeholder_info
53  * Fetch the PlaceHolderInfo for the given PHV
54  *
55  * If the PlaceHolderInfo doesn't exist yet, create it if create_new_ph is
56  * true, else throw an error.
57  *
58  * This is separate from make_placeholder_expr because subquery pullup has
59  * to make PlaceHolderVars for expressions that might not be used at all in
60  * the upper query, or might not remain after const-expression simplification.
61  * We build PlaceHolderInfos only for PHVs that are still present in the
62  * simplified query passed to query_planner().
63  *
64  * Note: this should only be called after query_planner() has started. Also,
65  * create_new_ph must not be TRUE after deconstruct_jointree begins, because
66  * make_outerjoininfo assumes that we already know about all placeholders.
67  */
70  bool create_new_ph)
71 {
72  PlaceHolderInfo *phinfo;
73  Relids rels_used;
74  ListCell *lc;
75 
76  /* if this ever isn't true, we'd need to be able to look in parent lists */
77  Assert(phv->phlevelsup == 0);
78 
79  foreach(lc, root->placeholder_list)
80  {
81  phinfo = (PlaceHolderInfo *) lfirst(lc);
82  if (phinfo->phid == phv->phid)
83  return phinfo;
84  }
85 
86  /* Not found, so create it */
87  if (!create_new_ph)
88  elog(ERROR, "too late to create a new PlaceHolderInfo");
89 
90  phinfo = makeNode(PlaceHolderInfo);
91 
92  phinfo->phid = phv->phid;
93  phinfo->ph_var = copyObject(phv);
94 
95  /*
96  * Any referenced rels that are outside the PHV's syntactic scope are
97  * LATERAL references, which should be included in ph_lateral but not in
98  * ph_eval_at. If no referenced rels are within the syntactic scope,
99  * force evaluation at the syntactic location.
100  */
101  rels_used = pull_varnos((Node *) phv->phexpr);
102  phinfo->ph_lateral = bms_difference(rels_used, phv->phrels);
103  if (bms_is_empty(phinfo->ph_lateral))
104  phinfo->ph_lateral = NULL; /* make it exactly NULL if empty */
105  phinfo->ph_eval_at = bms_int_members(rels_used, phv->phrels);
106  /* If no contained vars, force evaluation at syntactic location */
107  if (bms_is_empty(phinfo->ph_eval_at))
108  {
109  phinfo->ph_eval_at = bms_copy(phv->phrels);
110  Assert(!bms_is_empty(phinfo->ph_eval_at));
111  }
112  /* ph_eval_at may change later, see update_placeholder_eval_levels */
113  phinfo->ph_needed = NULL; /* initially it's unused */
114  /* for the moment, estimate width using just the datatype info */
115  phinfo->ph_width = get_typavgwidth(exprType((Node *) phv->phexpr),
116  exprTypmod((Node *) phv->phexpr));
117 
118  root->placeholder_list = lappend(root->placeholder_list, phinfo);
119 
120  /*
121  * The PHV's contained expression may contain other, lower-level PHVs. We
122  * now know we need to get those into the PlaceHolderInfo list, too, so we
123  * may as well do that immediately.
124  */
125  find_placeholders_in_expr(root, (Node *) phinfo->ph_var->phexpr);
126 
127  return phinfo;
128 }
129 
130 /*
131  * find_placeholders_in_jointree
132  * Search the jointree for PlaceHolderVars, and build PlaceHolderInfos
133  *
134  * We don't need to look at the targetlist because build_base_rel_tlists()
135  * will already have made entries for any PHVs in the tlist.
136  *
137  * This is called before we begin deconstruct_jointree. Once we begin
138  * deconstruct_jointree, all active placeholders must be present in
139  * root->placeholder_list, because make_outerjoininfo and
140  * update_placeholder_eval_levels require this info to be available
141  * while we crawl up the join tree.
142  */
143 void
145 {
146  /* We need do nothing if the query contains no PlaceHolderVars */
147  if (root->glob->lastPHId != 0)
148  {
149  /* Start recursion at top of jointree */
150  Assert(root->parse->jointree != NULL &&
151  IsA(root->parse->jointree, FromExpr));
152  find_placeholders_recurse(root, (Node *) root->parse->jointree);
153  }
154 }
155 
156 /*
157  * find_placeholders_recurse
158  * One recursion level of find_placeholders_in_jointree.
159  *
160  * jtnode is the current jointree node to examine.
161  */
162 static void
164 {
165  if (jtnode == NULL)
166  return;
167  if (IsA(jtnode, RangeTblRef))
168  {
169  /* No quals to deal with here */
170  }
171  else if (IsA(jtnode, FromExpr))
172  {
173  FromExpr *f = (FromExpr *) jtnode;
174  ListCell *l;
175 
176  /*
177  * First, recurse to handle child joins.
178  */
179  foreach(l, f->fromlist)
180  {
182  }
183 
184  /*
185  * Now process the top-level quals.
186  */
188  }
189  else if (IsA(jtnode, JoinExpr))
190  {
191  JoinExpr *j = (JoinExpr *) jtnode;
192 
193  /*
194  * First, recurse to handle child joins.
195  */
198 
199  /* Process the qual clauses */
201  }
202  else
203  elog(ERROR, "unrecognized node type: %d",
204  (int) nodeTag(jtnode));
205 }
206 
207 /*
208  * find_placeholders_in_expr
209  * Find all PlaceHolderVars in the given expression, and create
210  * PlaceHolderInfo entries for them.
211  */
212 static void
214 {
215  List *vars;
216  ListCell *vl;
217 
218  /*
219  * pull_var_clause does more than we need here, but it'll do and it's
220  * convenient to use.
221  */
222  vars = pull_var_clause(expr,
226  foreach(vl, vars)
227  {
228  PlaceHolderVar *phv = (PlaceHolderVar *) lfirst(vl);
229 
230  /* Ignore any plain Vars */
231  if (!IsA(phv, PlaceHolderVar))
232  continue;
233 
234  /* Create a PlaceHolderInfo entry if there's not one already */
235  (void) find_placeholder_info(root, phv, true);
236  }
237  list_free(vars);
238 }
239 
240 /*
241  * update_placeholder_eval_levels
242  * Adjust the target evaluation levels for placeholders
243  *
244  * The initial eval_at level set by find_placeholder_info was the set of
245  * rels used in the placeholder's expression (or the whole subselect below
246  * the placeholder's syntactic location, if the expr is variable-free).
247  * If the query contains any outer joins that can null any of those rels,
248  * we must delay evaluation to above those joins.
249  *
250  * We repeat this operation each time we add another outer join to
251  * root->join_info_list. It's somewhat annoying to have to do that, but
252  * since we don't have very much information on the placeholders' locations,
253  * it's hard to avoid. Each placeholder's eval_at level must be correct
254  * by the time it starts to figure in outer-join delay decisions for higher
255  * outer joins.
256  *
257  * In future we might want to put additional policy/heuristics here to
258  * try to determine an optimal evaluation level. The current rules will
259  * result in evaluation at the lowest possible level. However, pushing a
260  * placeholder eval up the tree is likely to further constrain evaluation
261  * order for outer joins, so it could easily be counterproductive; and we
262  * don't have enough information at this point to make an intelligent choice.
263  */
264 void
266 {
267  ListCell *lc1;
268 
269  foreach(lc1, root->placeholder_list)
270  {
271  PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc1);
272  Relids syn_level = phinfo->ph_var->phrels;
273  Relids eval_at;
274  bool found_some;
275  ListCell *lc2;
276 
277  /*
278  * We don't need to do any work on this placeholder unless the
279  * newly-added outer join is syntactically beneath its location.
280  */
281  if (!bms_is_subset(new_sjinfo->syn_lefthand, syn_level) ||
282  !bms_is_subset(new_sjinfo->syn_righthand, syn_level))
283  continue;
284 
285  /*
286  * Check for delays due to lower outer joins. This is the same logic
287  * as in check_outerjoin_delay in initsplan.c, except that we don't
288  * have anything to do with the delay_upper_joins flags; delay of
289  * upper outer joins will be handled later, based on the eval_at
290  * values we compute now.
291  */
292  eval_at = phinfo->ph_eval_at;
293 
294  do
295  {
296  found_some = false;
297  foreach(lc2, root->join_info_list)
298  {
299  SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc2);
300 
301  /* disregard joins not within the PHV's sub-select */
302  if (!bms_is_subset(sjinfo->syn_lefthand, syn_level) ||
303  !bms_is_subset(sjinfo->syn_righthand, syn_level))
304  continue;
305 
306  /* do we reference any nullable rels of this OJ? */
307  if (bms_overlap(eval_at, sjinfo->min_righthand) ||
308  (sjinfo->jointype == JOIN_FULL &&
309  bms_overlap(eval_at, sjinfo->min_lefthand)))
310  {
311  /* yes; have we included all its rels in eval_at? */
312  if (!bms_is_subset(sjinfo->min_lefthand, eval_at) ||
313  !bms_is_subset(sjinfo->min_righthand, eval_at))
314  {
315  /* no, so add them in */
316  eval_at = bms_add_members(eval_at,
317  sjinfo->min_lefthand);
318  eval_at = bms_add_members(eval_at,
319  sjinfo->min_righthand);
320  /* we'll need another iteration */
321  found_some = true;
322  }
323  }
324  }
325  } while (found_some);
326 
327  /* Can't move the PHV's eval_at level to above its syntactic level */
328  Assert(bms_is_subset(eval_at, syn_level));
329 
330  phinfo->ph_eval_at = eval_at;
331  }
332 }
333 
334 /*
335  * fix_placeholder_input_needed_levels
336  * Adjust the "needed at" levels for placeholder inputs
337  *
338  * This is called after we've finished determining the eval_at levels for
339  * all placeholders. We need to make sure that all vars and placeholders
340  * needed to evaluate each placeholder will be available at the scan or join
341  * level where the evaluation will be done. (It might seem that scan-level
342  * evaluations aren't interesting, but that's not so: a LATERAL reference
343  * within a placeholder's expression needs to cause the referenced var or
344  * placeholder to be marked as needed in the scan where it's evaluated.)
345  * Note that this loop can have side-effects on the ph_needed sets of other
346  * PlaceHolderInfos; that's okay because we don't examine ph_needed here, so
347  * there are no ordering issues to worry about.
348  */
349 void
351 {
352  ListCell *lc;
353 
354  foreach(lc, root->placeholder_list)
355  {
356  PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
357  List *vars = pull_var_clause((Node *) phinfo->ph_var->phexpr,
361 
362  add_vars_to_targetlist(root, vars, phinfo->ph_eval_at, false);
363  list_free(vars);
364  }
365 }
366 
367 /*
368  * add_placeholders_to_base_rels
369  * Add any required PlaceHolderVars to base rels' targetlists.
370  *
371  * If any placeholder can be computed at a base rel and is needed above it,
372  * add it to that rel's targetlist. This might look like it could be merged
373  * with fix_placeholder_input_needed_levels, but it must be separate because
374  * join removal happens in between, and can change the ph_eval_at sets. There
375  * is essentially the same logic in add_placeholders_to_joinrel, but we can't
376  * do that part until joinrels are formed.
377  */
378 void
380 {
381  ListCell *lc;
382 
383  foreach(lc, root->placeholder_list)
384  {
385  PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
386  Relids eval_at = phinfo->ph_eval_at;
387  int varno;
388 
389  if (bms_get_singleton_member(eval_at, &varno) &&
390  bms_nonempty_difference(phinfo->ph_needed, eval_at))
391  {
392  RelOptInfo *rel = find_base_rel(root, varno);
393 
394  rel->reltarget->exprs = lappend(rel->reltarget->exprs,
395  copyObject(phinfo->ph_var));
396  /* reltarget's cost and width fields will be updated later */
397  }
398  }
399 }
400 
401 /*
402  * add_placeholders_to_joinrel
403  * Add any required PlaceHolderVars to a join rel's targetlist;
404  * and if they contain lateral references, add those references to the
405  * joinrel's direct_lateral_relids.
406  *
407  * A join rel should emit a PlaceHolderVar if (a) the PHV is needed above
408  * this join level and (b) the PHV can be computed at or below this level.
409  */
410 void
412  RelOptInfo *outer_rel, RelOptInfo *inner_rel)
413 {
414  Relids relids = joinrel->relids;
415  ListCell *lc;
416 
417  foreach(lc, root->placeholder_list)
418  {
419  PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
420 
421  /* Is it still needed above this joinrel? */
422  if (bms_nonempty_difference(phinfo->ph_needed, relids))
423  {
424  /* Is it computable here? */
425  if (bms_is_subset(phinfo->ph_eval_at, relids))
426  {
427  /* Yup, add it to the output */
428  joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
429  phinfo->ph_var);
430  joinrel->reltarget->width += phinfo->ph_width;
431 
432  /*
433  * Charge the cost of evaluating the contained expression if
434  * the PHV can be computed here but not in either input. This
435  * is a bit bogus because we make the decision based on the
436  * first pair of possible input relations considered for the
437  * joinrel. With other pairs, it might be possible to compute
438  * the PHV in one input or the other, and then we'd be double
439  * charging the PHV's cost for some join paths. For now, live
440  * with that; but we might want to improve it later by
441  * refiguring the reltarget costs for each pair of inputs.
442  */
443  if (!bms_is_subset(phinfo->ph_eval_at, outer_rel->relids) &&
444  !bms_is_subset(phinfo->ph_eval_at, inner_rel->relids))
445  {
446  QualCost cost;
447 
448  cost_qual_eval_node(&cost, (Node *) phinfo->ph_var->phexpr,
449  root);
450  joinrel->reltarget->cost.startup += cost.startup;
451  joinrel->reltarget->cost.per_tuple += cost.per_tuple;
452  }
453 
454  /* Adjust joinrel's direct_lateral_relids as needed */
455  joinrel->direct_lateral_relids =
457  phinfo->ph_lateral);
458  }
459  }
460  }
461 }
void cost_qual_eval_node(QualCost *cost, Node *qual, PlannerInfo *root)
Definition: costsize.c:3225
Relids ph_needed
Definition: relation.h:1937
#define IsA(nodeptr, _type_)
Definition: nodes.h:559
Query * parse
Definition: relation.h:152
Bitmapset * bms_copy(const Bitmapset *a)
Definition: bitmapset.c:110
Relids ph_eval_at
Definition: relation.h:1935
PlaceHolderVar * ph_var
Definition: relation.h:1934
#define PVC_RECURSE_AGGREGATES
Definition: var.h:21
List * join_info_list
Definition: relation.h:247
Relids min_righthand
Definition: relation.h:1808
FromExpr * jointree
Definition: parsenodes.h:129
int32 exprTypmod(const Node *expr)
Definition: nodeFuncs.c:273
Bitmapset * bms_difference(const Bitmapset *a, const Bitmapset *b)
Definition: bitmapset.c:283
Definition: nodes.h:508
bool bms_get_singleton_member(const Bitmapset *a, int *member)
Definition: bitmapset.c:539
List * pull_var_clause(Node *node, int flags)
Definition: var.c:535
List * fromlist
Definition: primnodes.h:1433
void add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel, RelOptInfo *outer_rel, RelOptInfo *inner_rel)
Definition: placeholder.c:411
void add_placeholders_to_base_rels(PlannerInfo *root)
Definition: placeholder.c:379
Node * quals
Definition: primnodes.h:1434
Relids syn_lefthand
Definition: relation.h:1809
Cost startup
Definition: relation.h:45
void * copyObject(const void *from)
Definition: copyfuncs.c:4475
Node * larg
Definition: primnodes.h:1413
void add_vars_to_targetlist(PlannerInfo *root, List *vars, Relids where_needed, bool create_new_ph)
Definition: initsplan.c:197
Relids syn_righthand
Definition: relation.h:1810
#define PVC_INCLUDE_PLACEHOLDERS
Definition: var.h:24
PlaceHolderVar * make_placeholder_expr(PlannerInfo *root, Expr *expr, Relids phrels)
Definition: placeholder.c:39
Cost per_tuple
Definition: relation.h:46
Relids phrels
Definition: relation.h:1741
#define ERROR
Definition: elog.h:43
Expr * phexpr
Definition: relation.h:1740
bool bms_is_subset(const Bitmapset *a, const Bitmapset *b)
Definition: bitmapset.c:307
PlannerGlobal * glob
Definition: relation.h:154
PlaceHolderInfo * find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv, bool create_new_ph)
Definition: placeholder.c:69
#define PVC_RECURSE_WINDOWFUNCS
Definition: var.h:23
Relids relids
Definition: relation.h:490
Relids pull_varnos(Node *node)
Definition: var.c:95
List * lappend(List *list, void *datum)
Definition: list.c:128
void fix_placeholder_input_needed_levels(PlannerInfo *root)
Definition: placeholder.c:350
bool bms_is_empty(const Bitmapset *a)
Definition: bitmapset.c:633
void find_placeholders_in_jointree(PlannerInfo *root)
Definition: placeholder.c:144
List * exprs
Definition: relation.h:824
Relids direct_lateral_relids
Definition: relation.h:514
Node * quals
Definition: primnodes.h:1416
Index lastPHId
Definition: relation.h:116
Relids ph_lateral
Definition: relation.h:1936
int32 get_typavgwidth(Oid typid, int32 typmod)
Definition: lsyscache.c:2296
static void find_placeholders_recurse(PlannerInfo *root, Node *jtnode)
Definition: placeholder.c:163
#define makeNode(_type_)
Definition: nodes.h:556
Node * rarg
Definition: primnodes.h:1414
#define NULL
Definition: c.h:226
#define Assert(condition)
Definition: c.h:670
#define lfirst(lc)
Definition: pg_list.h:106
JoinType jointype
Definition: relation.h:1811
QualCost cost
Definition: relation.h:826
Oid exprType(const Node *expr)
Definition: nodeFuncs.c:42
#define nodeTag(nodeptr)
Definition: nodes.h:513
void update_placeholder_eval_levels(PlannerInfo *root, SpecialJoinInfo *new_sjinfo)
Definition: placeholder.c:265
bool bms_overlap(const Bitmapset *a, const Bitmapset *b)
Definition: bitmapset.c:442
int width
Definition: relation.h:827
Index phlevelsup
Definition: relation.h:1743
void list_free(List *list)
Definition: list.c:1133
List * placeholder_list
Definition: relation.h:253
static void find_placeholders_in_expr(PlannerInfo *root, Node *expr)
Definition: placeholder.c:213
#define elog
Definition: elog.h:219
RelOptInfo * find_base_rel(PlannerInfo *root, int relid)
Definition: relnode.c:219
Bitmapset * bms_int_members(Bitmapset *a, const Bitmapset *b)
Definition: bitmapset.c:761
Definition: regcomp.c:226
Definition: pg_list.h:45
struct PathTarget * reltarget
Definition: relation.h:501
Relids min_lefthand
Definition: relation.h:1807
Bitmapset * bms_add_members(Bitmapset *a, const Bitmapset *b)
Definition: bitmapset.c:725
bool bms_nonempty_difference(const Bitmapset *a, const Bitmapset *b)
Definition: bitmapset.c:464