Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * pgpa_scan.c
4 : * analysis of scans in Plan trees
5 : *
6 : * Copyright (c) 2016-2026, PostgreSQL Global Development Group
7 : *
8 : * contrib/pg_plan_advice/pgpa_scan.c
9 : *
10 : *-------------------------------------------------------------------------
11 : */
12 : #include "postgres.h"
13 :
14 : #include "pgpa_scan.h"
15 : #include "pgpa_walker.h"
16 :
17 : #include "nodes/parsenodes.h"
18 : #include "parser/parsetree.h"
19 :
20 : static pgpa_scan *pgpa_make_scan(pgpa_plan_walker_context *walker, Plan *plan,
21 : pgpa_scan_strategy strategy,
22 : Bitmapset *relids);
23 :
24 :
25 : static RTEKind unique_nonjoin_rtekind(Bitmapset *relids, List *rtable);
26 :
27 : /*
28 : * Build a pgpa_scan object for a Plan node and update the plan walker
29 : * context as appropriate. If this is an Append or MergeAppend scan, also
30 : * build pgpa_scan for any scans that were consolidated into this one by
31 : * Append/MergeAppend pull-up.
32 : *
33 : * If there is at least one ElidedNode for this plan node, pass the uppermost
34 : * one as elided_node, else pass NULL.
35 : *
36 : * Set the 'beneath_any_gather' node if we are underneath a Gather or
37 : * Gather Merge node (except for a single-copy Gather node, for which
38 : * GATHER or GATHER_MERGE advice should not be emitted).
39 : *
40 : * Set the 'within_join_problem' flag if we're inside of a join problem and
41 : * not otherwise.
42 : */
43 : pgpa_scan *
44 384 : pgpa_build_scan(pgpa_plan_walker_context *walker, Plan *plan,
45 : ElidedNode *elided_node,
46 : bool beneath_any_gather, bool within_join_problem)
47 : {
48 384 : pgpa_scan_strategy strategy = PGPA_SCAN_ORDINARY;
49 384 : Bitmapset *relids = NULL;
50 384 : int rti = -1;
51 384 : List *child_append_relid_sets = NIL;
52 384 : NodeTag nodetype = nodeTag(plan);
53 :
54 384 : if (elided_node != NULL)
55 : {
56 8 : nodetype = elided_node->elided_type;
57 8 : relids = elided_node->relids;
58 :
59 : /*
60 : * If setrefs processing elided an Append or MergeAppend node that had
61 : * only one surviving child, it could be either a partitionwise
62 : * operation or a setop over subqueries, depending on the rtekind.
63 : *
64 : * A setop over subqueries, or a trivial SubqueryScan that was elided,
65 : * is an "ordinary" scan i.e. one for which we do not need to generate
66 : * advice because the planner has not made any meaningful choice.
67 : *
68 : * Note that the PGPA_SCAN_PARTITIONWISE case also includes
69 : * partitionwise joins; this module considers those to be a form of
70 : * scan, since they lack internal structure that we can decompose.
71 : */
72 8 : if ((nodetype == T_Append || nodetype == T_MergeAppend) &&
73 0 : unique_nonjoin_rtekind(relids,
74 0 : walker->pstmt->rtable) == RTE_RELATION)
75 0 : strategy = PGPA_SCAN_PARTITIONWISE;
76 : else
77 8 : strategy = PGPA_SCAN_ORDINARY;
78 :
79 : /* Join RTIs can be present, but advice never refers to them. */
80 8 : relids = pgpa_filter_out_join_relids(relids, walker->pstmt->rtable);
81 : }
82 376 : else if ((rti = pgpa_scanrelid(plan)) != 0)
83 : {
84 258 : relids = bms_make_singleton(rti);
85 :
86 258 : switch (nodeTag(plan))
87 : {
88 160 : case T_SeqScan:
89 160 : strategy = PGPA_SCAN_SEQ;
90 160 : break;
91 3 : case T_BitmapHeapScan:
92 3 : strategy = PGPA_SCAN_BITMAP_HEAP;
93 3 : break;
94 65 : case T_IndexScan:
95 65 : strategy = PGPA_SCAN_INDEX;
96 65 : break;
97 7 : case T_IndexOnlyScan:
98 7 : strategy = PGPA_SCAN_INDEX_ONLY;
99 7 : break;
100 4 : case T_TidScan:
101 : case T_TidRangeScan:
102 4 : strategy = PGPA_SCAN_TID;
103 4 : break;
104 19 : default:
105 :
106 : /*
107 : * This case includes a ForeignScan targeting a single
108 : * relation; no other strategy is possible in that case, but
109 : * see below, where things are different in multi-relation
110 : * cases.
111 : */
112 19 : strategy = PGPA_SCAN_ORDINARY;
113 19 : break;
114 : }
115 : }
116 118 : else if ((relids = pgpa_relids(plan)) != NULL)
117 : {
118 22 : switch (nodeTag(plan))
119 : {
120 0 : case T_ForeignScan:
121 :
122 : /*
123 : * If multiple relations are being targeted by a single
124 : * foreign scan, then the foreign join has been pushed to the
125 : * remote side, and we want that to be reflected in the
126 : * generated advice.
127 : */
128 0 : strategy = PGPA_SCAN_FOREIGN;
129 0 : break;
130 11 : case T_Append:
131 :
132 : /*
133 : * Append nodes can represent partitionwise scans of a
134 : * relation, but when they implement a set operation, they are
135 : * just ordinary scans.
136 : */
137 11 : if (unique_nonjoin_rtekind(relids, walker->pstmt->rtable)
138 : == RTE_RELATION)
139 11 : strategy = PGPA_SCAN_PARTITIONWISE;
140 : else
141 0 : strategy = PGPA_SCAN_ORDINARY;
142 :
143 : /* Be sure to account for pulled-up scans. */
144 11 : child_append_relid_sets =
145 : ((Append *) plan)->child_append_relid_sets;
146 11 : break;
147 0 : case T_MergeAppend:
148 : /* Same logic here as for Append, above. */
149 0 : if (unique_nonjoin_rtekind(relids, walker->pstmt->rtable)
150 : == RTE_RELATION)
151 0 : strategy = PGPA_SCAN_PARTITIONWISE;
152 : else
153 0 : strategy = PGPA_SCAN_ORDINARY;
154 :
155 : /* Be sure to account for pulled-up scans. */
156 0 : child_append_relid_sets =
157 : ((MergeAppend *) plan)->child_append_relid_sets;
158 0 : break;
159 11 : default:
160 11 : strategy = PGPA_SCAN_ORDINARY;
161 11 : break;
162 : }
163 :
164 :
165 : /* Join RTIs can be present, but advice never refers to them. */
166 22 : relids = pgpa_filter_out_join_relids(relids, walker->pstmt->rtable);
167 : }
168 :
169 : /*
170 : * If this is an Append or MergeAppend node into which subordinate Append
171 : * or MergeAppend paths were merged, each of those merged paths is
172 : * effectively another scan for which we need to account.
173 : */
174 768 : foreach_node(Bitmapset, child_relids, child_append_relid_sets)
175 : {
176 : Bitmapset *child_nonjoin_relids;
177 :
178 : child_nonjoin_relids =
179 0 : pgpa_filter_out_join_relids(child_relids,
180 0 : walker->pstmt->rtable);
181 0 : (void) pgpa_make_scan(walker, plan, strategy,
182 : child_nonjoin_relids);
183 : }
184 :
185 : /*
186 : * If this plan node has no associated RTIs, it's not a scan. When the
187 : * 'within_join_problem' flag is set, that's unexpected, so throw an
188 : * error, else return quietly.
189 : */
190 384 : if (relids == NULL)
191 : {
192 96 : if (within_join_problem)
193 0 : elog(ERROR, "plan node has no RTIs: %d", (int) nodeTag(plan));
194 96 : return NULL;
195 : }
196 :
197 : /*
198 : * Add the appropriate set of RTIs to walker->no_gather_scans.
199 : *
200 : * Add nothing if we're beneath a Gather or Gather Merge node, since
201 : * NO_GATHER advice is clearly inappropriate in that situation.
202 : *
203 : * Add nothing if this is an Append or MergeAppend node, whether or not
204 : * elided. We'll emit NO_GATHER() for the underlying scan, which is good
205 : * enough.
206 : */
207 288 : if (!beneath_any_gather && nodetype != T_Append &&
208 : nodetype != T_MergeAppend)
209 256 : walker->no_gather_scans =
210 256 : bms_add_members(walker->no_gather_scans, relids);
211 :
212 : /* Caller tells us whether NO_GATHER() advice for this scan is needed. */
213 288 : return pgpa_make_scan(walker, plan, strategy, relids);
214 : }
215 :
216 : /*
217 : * Create a single pgpa_scan object and update the pgpa_plan_walker_context.
218 : */
219 : static pgpa_scan *
220 288 : pgpa_make_scan(pgpa_plan_walker_context *walker, Plan *plan,
221 : pgpa_scan_strategy strategy, Bitmapset *relids)
222 : {
223 : pgpa_scan *scan;
224 :
225 : /* Create the scan object. */
226 288 : scan = palloc(sizeof(pgpa_scan));
227 288 : scan->plan = plan;
228 288 : scan->strategy = strategy;
229 288 : scan->relids = relids;
230 :
231 : /* Add it to the appropriate list. */
232 288 : walker->scans[scan->strategy] = lappend(walker->scans[scan->strategy],
233 : scan);
234 :
235 288 : return scan;
236 : }
237 :
238 : /*
239 : * Determine the unique rtekind of a set of relids.
240 : */
241 : static RTEKind
242 11 : unique_nonjoin_rtekind(Bitmapset *relids, List *rtable)
243 : {
244 11 : int rti = -1;
245 11 : bool first = true;
246 11 : RTEKind rtekind = RTE_RELATION; /* silence compiler warning */
247 :
248 : Assert(relids != NULL);
249 :
250 31 : while ((rti = bms_next_member(relids, rti)) >= 0)
251 : {
252 20 : RangeTblEntry *rte = rt_fetch(rti, rtable);
253 :
254 20 : if (rte->rtekind == RTE_JOIN)
255 0 : continue;
256 :
257 20 : if (first)
258 : {
259 11 : rtekind = rte->rtekind;
260 11 : first = false;
261 : }
262 9 : else if (rtekind != rte->rtekind)
263 0 : elog(ERROR, "rtekind mismatch: %d vs. %d",
264 : rtekind, rte->rtekind);
265 : }
266 :
267 11 : if (first)
268 0 : elog(ERROR, "no non-RTE_JOIN RTEs found");
269 :
270 11 : return rtekind;
271 : }
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