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execJunk.c
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1 /*-------------------------------------------------------------------------
2  *
3  * execJunk.c
4  * Junk attribute support stuff....
5  *
6  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
7  * Portions Copyright (c) 1994, Regents of the University of California
8  *
9  *
10  * IDENTIFICATION
11  * src/backend/executor/execJunk.c
12  *
13  *-------------------------------------------------------------------------
14  */
15 #include "postgres.h"
16 
17 #include "executor/executor.h"
18 
19 /*-------------------------------------------------------------------------
20  * XXX this stuff should be rewritten to take advantage
21  * of ExecProject() and the ProjectionInfo node.
22  * -cim 6/3/91
23  *
24  * An attribute of a tuple living inside the executor, can be
25  * either a normal attribute or a "junk" attribute. "junk" attributes
26  * never make it out of the executor, i.e. they are never printed,
27  * returned or stored on disk. Their only purpose in life is to
28  * store some information useful only to the executor, mainly the values
29  * of system attributes like "ctid", or sort key columns that are not to
30  * be output.
31  *
32  * The general idea is the following: A target list consists of a list of
33  * TargetEntry nodes containing expressions. Each TargetEntry has a field
34  * called 'resjunk'. If the value of this field is true then the
35  * corresponding attribute is a "junk" attribute.
36  *
37  * When we initialize a plan we call ExecInitJunkFilter to create a filter.
38  *
39  * We then execute the plan, treating the resjunk attributes like any others.
40  *
41  * Finally, when at the top level we get back a tuple, we can call
42  * ExecFindJunkAttribute/ExecGetJunkAttribute to retrieve the values of the
43  * junk attributes we are interested in, and ExecFilterJunk to remove all the
44  * junk attributes from a tuple. This new "clean" tuple is then printed,
45  * inserted, or updated.
46  *
47  *-------------------------------------------------------------------------
48  */
49 
50 /*
51  * ExecInitJunkFilter
52  *
53  * Initialize the Junk filter.
54  *
55  * The source targetlist is passed in. The output tuple descriptor is
56  * built from the non-junk tlist entries.
57  * An optional resultSlot can be passed as well; otherwise, we create one.
58  */
59 JunkFilter *
61 {
62  JunkFilter *junkfilter;
63  TupleDesc cleanTupType;
64  int cleanLength;
65  AttrNumber *cleanMap;
66 
67  /*
68  * Compute the tuple descriptor for the cleaned tuple.
69  */
70  cleanTupType = ExecCleanTypeFromTL(targetList);
71 
72  /*
73  * Use the given slot, or make a new slot if we weren't given one.
74  */
75  if (slot)
76  ExecSetSlotDescriptor(slot, cleanTupType);
77  else
78  slot = MakeSingleTupleTableSlot(cleanTupType, &TTSOpsVirtual);
79 
80  /*
81  * Now calculate the mapping between the original tuple's attributes and
82  * the "clean" tuple's attributes.
83  *
84  * The "map" is an array of "cleanLength" attribute numbers, i.e. one
85  * entry for every attribute of the "clean" tuple. The value of this entry
86  * is the attribute number of the corresponding attribute of the
87  * "original" tuple. (Zero indicates a NULL output attribute, but we do
88  * not use that feature in this routine.)
89  */
90  cleanLength = cleanTupType->natts;
91  if (cleanLength > 0)
92  {
93  AttrNumber cleanResno;
94  ListCell *t;
95 
96  cleanMap = (AttrNumber *) palloc(cleanLength * sizeof(AttrNumber));
97  cleanResno = 0;
98  foreach(t, targetList)
99  {
100  TargetEntry *tle = lfirst(t);
101 
102  if (!tle->resjunk)
103  {
104  cleanMap[cleanResno] = tle->resno;
105  cleanResno++;
106  }
107  }
108  Assert(cleanResno == cleanLength);
109  }
110  else
111  cleanMap = NULL;
112 
113  /*
114  * Finally create and initialize the JunkFilter struct.
115  */
116  junkfilter = makeNode(JunkFilter);
117 
118  junkfilter->jf_targetList = targetList;
119  junkfilter->jf_cleanTupType = cleanTupType;
120  junkfilter->jf_cleanMap = cleanMap;
121  junkfilter->jf_resultSlot = slot;
122 
123  return junkfilter;
124 }
125 
126 /*
127  * ExecInitJunkFilterConversion
128  *
129  * Initialize a JunkFilter for rowtype conversions.
130  *
131  * Here, we are given the target "clean" tuple descriptor rather than
132  * inferring it from the targetlist. The target descriptor can contain
133  * deleted columns. It is assumed that the caller has checked that the
134  * non-deleted columns match up with the non-junk columns of the targetlist.
135  */
136 JunkFilter *
138  TupleDesc cleanTupType,
139  TupleTableSlot *slot)
140 {
141  JunkFilter *junkfilter;
142  int cleanLength;
143  AttrNumber *cleanMap;
144  ListCell *t;
145  int i;
146 
147  /*
148  * Use the given slot, or make a new slot if we weren't given one.
149  */
150  if (slot)
151  ExecSetSlotDescriptor(slot, cleanTupType);
152  else
153  slot = MakeSingleTupleTableSlot(cleanTupType, &TTSOpsVirtual);
154 
155  /*
156  * Calculate the mapping between the original tuple's attributes and the
157  * "clean" tuple's attributes.
158  *
159  * The "map" is an array of "cleanLength" attribute numbers, i.e. one
160  * entry for every attribute of the "clean" tuple. The value of this entry
161  * is the attribute number of the corresponding attribute of the
162  * "original" tuple. We store zero for any deleted attributes, marking
163  * that a NULL is needed in the output tuple.
164  */
165  cleanLength = cleanTupType->natts;
166  if (cleanLength > 0)
167  {
168  cleanMap = (AttrNumber *) palloc0(cleanLength * sizeof(AttrNumber));
169  t = list_head(targetList);
170  for (i = 0; i < cleanLength; i++)
171  {
172  if (TupleDescAttr(cleanTupType, i)->attisdropped)
173  continue; /* map entry is already zero */
174  for (;;)
175  {
176  TargetEntry *tle = lfirst(t);
177 
178  t = lnext(targetList, t);
179  if (!tle->resjunk)
180  {
181  cleanMap[i] = tle->resno;
182  break;
183  }
184  }
185  }
186  }
187  else
188  cleanMap = NULL;
189 
190  /*
191  * Finally create and initialize the JunkFilter struct.
192  */
193  junkfilter = makeNode(JunkFilter);
194 
195  junkfilter->jf_targetList = targetList;
196  junkfilter->jf_cleanTupType = cleanTupType;
197  junkfilter->jf_cleanMap = cleanMap;
198  junkfilter->jf_resultSlot = slot;
199 
200  return junkfilter;
201 }
202 
203 /*
204  * ExecFindJunkAttribute
205  *
206  * Locate the specified junk attribute in the junk filter's targetlist,
207  * and return its resno. Returns InvalidAttrNumber if not found.
208  */
210 ExecFindJunkAttribute(JunkFilter *junkfilter, const char *attrName)
211 {
212  return ExecFindJunkAttributeInTlist(junkfilter->jf_targetList, attrName);
213 }
214 
215 /*
216  * ExecFindJunkAttributeInTlist
217  *
218  * Find a junk attribute given a subplan's targetlist (not necessarily
219  * part of a JunkFilter).
220  */
222 ExecFindJunkAttributeInTlist(List *targetlist, const char *attrName)
223 {
224  ListCell *t;
225 
226  foreach(t, targetlist)
227  {
228  TargetEntry *tle = lfirst(t);
229 
230  if (tle->resjunk && tle->resname &&
231  (strcmp(tle->resname, attrName) == 0))
232  {
233  /* We found it ! */
234  return tle->resno;
235  }
236  }
237 
238  return InvalidAttrNumber;
239 }
240 
241 /*
242  * ExecFilterJunk
243  *
244  * Construct and return a slot with all the junk attributes removed.
245  */
248 {
249  TupleTableSlot *resultSlot;
250  AttrNumber *cleanMap;
251  TupleDesc cleanTupType;
252  int cleanLength;
253  int i;
254  Datum *values;
255  bool *isnull;
256  Datum *old_values;
257  bool *old_isnull;
258 
259  /*
260  * Extract all the values of the old tuple.
261  */
262  slot_getallattrs(slot);
263  old_values = slot->tts_values;
264  old_isnull = slot->tts_isnull;
265 
266  /*
267  * get info from the junk filter
268  */
269  cleanTupType = junkfilter->jf_cleanTupType;
270  cleanLength = cleanTupType->natts;
271  cleanMap = junkfilter->jf_cleanMap;
272  resultSlot = junkfilter->jf_resultSlot;
273 
274  /*
275  * Prepare to build a virtual result tuple.
276  */
277  ExecClearTuple(resultSlot);
278  values = resultSlot->tts_values;
279  isnull = resultSlot->tts_isnull;
280 
281  /*
282  * Transpose data into proper fields of the new tuple.
283  */
284  for (i = 0; i < cleanLength; i++)
285  {
286  int j = cleanMap[i];
287 
288  if (j == 0)
289  {
290  values[i] = (Datum) 0;
291  isnull[i] = true;
292  }
293  else
294  {
295  values[i] = old_values[j - 1];
296  isnull[i] = old_isnull[j - 1];
297  }
298  }
299 
300  /*
301  * And return the virtual tuple.
302  */
303  return ExecStoreVirtualTuple(resultSlot);
304 }
AttrNumber * jf_cleanMap
Definition: execnodes.h:367
static TupleTableSlot * ExecClearTuple(TupleTableSlot *slot)
Definition: tuptable.h:425
static ListCell * lnext(const List *l, const ListCell *c)
Definition: pg_list.h:322
TupleDesc ExecCleanTypeFromTL(List *targetList)
Definition: execTuples.c:1950
AttrNumber ExecFindJunkAttributeInTlist(List *targetlist, const char *attrName)
Definition: execJunk.c:222
TupleTableSlot * MakeSingleTupleTableSlot(TupleDesc tupdesc, const TupleTableSlotOps *tts_ops)
Definition: execTuples.c:1238
AttrNumber ExecFindJunkAttribute(JunkFilter *junkfilter, const char *attrName)
Definition: execJunk.c:210
#define TupleDescAttr(tupdesc, i)
Definition: tupdesc.h:92
JunkFilter * ExecInitJunkFilterConversion(List *targetList, TupleDesc cleanTupType, TupleTableSlot *slot)
Definition: execJunk.c:137
const TupleTableSlotOps TTSOpsVirtual
Definition: execTuples.c:83
List * jf_targetList
Definition: execnodes.h:365
TupleTableSlot * jf_resultSlot
Definition: execnodes.h:368
Datum * tts_values
Definition: tuptable.h:126
char * resname
Definition: primnodes.h:1446
bool resjunk
Definition: primnodes.h:1451
static void slot_getallattrs(TupleTableSlot *slot)
Definition: tuptable.h:354
bool * tts_isnull
Definition: tuptable.h:128
TupleDesc jf_cleanTupType
Definition: execnodes.h:366
AttrNumber resno
Definition: primnodes.h:1445
static ListCell * list_head(const List *l)
Definition: pg_list.h:125
void * palloc0(Size size)
Definition: mcxt.c:1093
uintptr_t Datum
Definition: postgres.h:411
TupleTableSlot * ExecFilterJunk(JunkFilter *junkfilter, TupleTableSlot *slot)
Definition: execJunk.c:247
void ExecSetSlotDescriptor(TupleTableSlot *slot, TupleDesc tupdesc)
Definition: execTuples.c:1289
#define makeNode(_type_)
Definition: nodes.h:587
#define Assert(condition)
Definition: c.h:804
#define lfirst(lc)
Definition: pg_list.h:169
#define InvalidAttrNumber
Definition: attnum.h:23
static Datum values[MAXATTR]
Definition: bootstrap.c:166
void * palloc(Size size)
Definition: mcxt.c:1062
int i
bool isnull
Definition: execExpr.h:337
Definition: pg_list.h:50
int16 AttrNumber
Definition: attnum.h:21
JunkFilter * ExecInitJunkFilter(List *targetList, TupleTableSlot *slot)
Definition: execJunk.c:60
TupleTableSlot * ExecStoreVirtualTuple(TupleTableSlot *slot)
Definition: execTuples.c:1552