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toast_helper.c
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1 /*-------------------------------------------------------------------------
2  *
3  * toast_helper.c
4  * Helper functions for table AMs implementing compressed or
5  * out-of-line storage of varlena attributes.
6  *
7  * Copyright (c) 2000-2021, PostgreSQL Global Development Group
8  *
9  * IDENTIFICATION
10  * src/backend/access/table/toast_helper.c
11  *
12  *-------------------------------------------------------------------------
13  */
14 
15 #include "postgres.h"
16 
17 #include "access/detoast.h"
18 #include "access/table.h"
19 #include "access/toast_helper.h"
20 #include "access/toast_internals.h"
21 #include "catalog/pg_type_d.h"
22 
23 
24 /*
25  * Prepare to TOAST a tuple.
26  *
27  * tupleDesc, toast_values, and toast_isnull are required parameters; they
28  * provide the necessary details about the tuple to be toasted.
29  *
30  * toast_oldvalues and toast_oldisnull should be NULL for a newly-inserted
31  * tuple; for an update, they should describe the existing tuple.
32  *
33  * All of these arrays should have a length equal to tupleDesc->natts.
34  *
35  * On return, toast_flags and toast_attr will have been initialized.
36  * toast_flags is just a single uint8, but toast_attr is an caller-provided
37  * array with a length equal to tupleDesc->natts. The caller need not
38  * perform any initialization of the array before calling this function.
39  */
40 void
42 {
43  TupleDesc tupleDesc = ttc->ttc_rel->rd_att;
44  int numAttrs = tupleDesc->natts;
45  int i;
46 
47  ttc->ttc_flags = 0;
48 
49  for (i = 0; i < numAttrs; i++)
50  {
51  Form_pg_attribute att = TupleDescAttr(tupleDesc, i);
52  struct varlena *old_value;
53  struct varlena *new_value;
54 
55  ttc->ttc_attr[i].tai_colflags = 0;
56  ttc->ttc_attr[i].tai_oldexternal = NULL;
57  ttc->ttc_attr[i].tai_compression = att->attcompression;
58 
59  if (ttc->ttc_oldvalues != NULL)
60  {
61  /*
62  * For UPDATE get the old and new values of this attribute
63  */
64  old_value =
65  (struct varlena *) DatumGetPointer(ttc->ttc_oldvalues[i]);
66  new_value =
67  (struct varlena *) DatumGetPointer(ttc->ttc_values[i]);
68 
69  /*
70  * If the old value is stored on disk, check if it has changed so
71  * we have to delete it later.
72  */
73  if (att->attlen == -1 && !ttc->ttc_oldisnull[i] &&
74  VARATT_IS_EXTERNAL_ONDISK(old_value))
75  {
76  if (ttc->ttc_isnull[i] ||
77  !VARATT_IS_EXTERNAL_ONDISK(new_value) ||
78  memcmp((char *) old_value, (char *) new_value,
79  VARSIZE_EXTERNAL(old_value)) != 0)
80  {
81  /*
82  * The old external stored value isn't needed any more
83  * after the update
84  */
87  }
88  else
89  {
90  /*
91  * This attribute isn't changed by this update so we reuse
92  * the original reference to the old value in the new
93  * tuple.
94  */
96  continue;
97  }
98  }
99  }
100  else
101  {
102  /*
103  * For INSERT simply get the new value
104  */
105  new_value = (struct varlena *) DatumGetPointer(ttc->ttc_values[i]);
106  }
107 
108  /*
109  * Handle NULL attributes
110  */
111  if (ttc->ttc_isnull[i])
112  {
114  ttc->ttc_flags |= TOAST_HAS_NULLS;
115  continue;
116  }
117 
118  /*
119  * Now look at varlena attributes
120  */
121  if (att->attlen == -1)
122  {
123  /*
124  * If the table's attribute says PLAIN always, force it so.
125  */
126  if (att->attstorage == TYPSTORAGE_PLAIN)
128 
129  /*
130  * We took care of UPDATE above, so any external value we find
131  * still in the tuple must be someone else's that we cannot reuse
132  * (this includes the case of an out-of-line in-memory datum).
133  * Fetch it back (without decompression, unless we are forcing
134  * PLAIN storage). If necessary, we'll push it out as a new
135  * external value below.
136  */
137  if (VARATT_IS_EXTERNAL(new_value))
138  {
139  ttc->ttc_attr[i].tai_oldexternal = new_value;
140  if (att->attstorage == TYPSTORAGE_PLAIN)
141  new_value = detoast_attr(new_value);
142  else
143  new_value = detoast_external_attr(new_value);
144  ttc->ttc_values[i] = PointerGetDatum(new_value);
147  }
148 
149  /*
150  * Remember the size of this attribute
151  */
152  ttc->ttc_attr[i].tai_size = VARSIZE_ANY(new_value);
153  }
154  else
155  {
156  /*
157  * Not a varlena attribute, plain storage always
158  */
160  }
161  }
162 }
163 
164 /*
165  * Find the largest varlena attribute that satisfies certain criteria.
166  *
167  * The relevant column must not be marked TOASTCOL_IGNORE, and if the
168  * for_compression flag is passed as true, it must also not be marked
169  * TOASTCOL_INCOMPRESSIBLE.
170  *
171  * The column must have attstorage EXTERNAL or EXTENDED if check_main is
172  * false, and must have attstorage MAIN if check_main is true.
173  *
174  * The column must have a minimum size of MAXALIGN(TOAST_POINTER_SIZE);
175  * if not, no benefit is to be expected by compressing it.
176  *
177  * The return value is the index of the biggest suitable column, or
178  * -1 if there is none.
179  */
180 int
182  bool for_compression, bool check_main)
183 {
184  TupleDesc tupleDesc = ttc->ttc_rel->rd_att;
185  int numAttrs = tupleDesc->natts;
186  int biggest_attno = -1;
187  int32 biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
188  int32 skip_colflags = TOASTCOL_IGNORE;
189  int i;
190 
191  if (for_compression)
192  skip_colflags |= TOASTCOL_INCOMPRESSIBLE;
193 
194  for (i = 0; i < numAttrs; i++)
195  {
196  Form_pg_attribute att = TupleDescAttr(tupleDesc, i);
197 
198  if ((ttc->ttc_attr[i].tai_colflags & skip_colflags) != 0)
199  continue;
201  continue; /* can't happen, toast_action would be PLAIN */
202  if (for_compression &&
204  continue;
205  if (check_main && att->attstorage != TYPSTORAGE_MAIN)
206  continue;
207  if (!check_main && att->attstorage != TYPSTORAGE_EXTENDED &&
208  att->attstorage != TYPSTORAGE_EXTERNAL)
209  continue;
210 
211  if (ttc->ttc_attr[i].tai_size > biggest_size)
212  {
213  biggest_attno = i;
214  biggest_size = ttc->ttc_attr[i].tai_size;
215  }
216  }
217 
218  return biggest_attno;
219 }
220 
221 /*
222  * Try compression for an attribute.
223  *
224  * If we find that the attribute is not compressible, mark it so.
225  */
226 void
228 {
229  Datum *value = &ttc->ttc_values[attribute];
230  Datum new_value;
231  ToastAttrInfo *attr = &ttc->ttc_attr[attribute];
232 
233  new_value = toast_compress_datum(*value, attr->tai_compression);
234 
235  if (DatumGetPointer(new_value) != NULL)
236  {
237  /* successful compression */
238  if ((attr->tai_colflags & TOASTCOL_NEEDS_FREE) != 0)
239  pfree(DatumGetPointer(*value));
240  *value = new_value;
242  attr->tai_size = VARSIZE(DatumGetPointer(*value));
244  }
245  else
246  {
247  /* incompressible, ignore on subsequent compression passes */
249  }
250 }
251 
252 /*
253  * Move an attribute to external storage.
254  */
255 void
257 {
258  Datum *value = &ttc->ttc_values[attribute];
259  Datum old_value = *value;
260  ToastAttrInfo *attr = &ttc->ttc_attr[attribute];
261 
262  attr->tai_colflags |= TOASTCOL_IGNORE;
263  *value = toast_save_datum(ttc->ttc_rel, old_value, attr->tai_oldexternal,
264  options);
265  if ((attr->tai_colflags & TOASTCOL_NEEDS_FREE) != 0)
266  pfree(DatumGetPointer(old_value));
269 }
270 
271 /*
272  * Perform appropriate cleanup after one tuple has been subjected to TOAST.
273  */
274 void
276 {
277  TupleDesc tupleDesc = ttc->ttc_rel->rd_att;
278  int numAttrs = tupleDesc->natts;
279 
280  /*
281  * Free allocated temp values
282  */
283  if ((ttc->ttc_flags & TOAST_NEEDS_FREE) != 0)
284  {
285  int i;
286 
287  for (i = 0; i < numAttrs; i++)
288  {
289  ToastAttrInfo *attr = &ttc->ttc_attr[i];
290 
291  if ((attr->tai_colflags & TOASTCOL_NEEDS_FREE) != 0)
292  pfree(DatumGetPointer(ttc->ttc_values[i]));
293  }
294  }
295 
296  /*
297  * Delete external values from the old tuple
298  */
299  if ((ttc->ttc_flags & TOAST_NEEDS_DELETE_OLD) != 0)
300  {
301  int i;
302 
303  for (i = 0; i < numAttrs; i++)
304  {
305  ToastAttrInfo *attr = &ttc->ttc_attr[i];
306 
307  if ((attr->tai_colflags & TOASTCOL_NEEDS_DELETE_OLD) != 0)
308  toast_delete_datum(ttc->ttc_rel, ttc->ttc_oldvalues[i], false);
309  }
310  }
311 }
312 
313 /*
314  * Check for external stored attributes and delete them from the secondary
315  * relation.
316  */
317 void
319  bool is_speculative)
320 {
321  TupleDesc tupleDesc = rel->rd_att;
322  int numAttrs = tupleDesc->natts;
323  int i;
324 
325  for (i = 0; i < numAttrs; i++)
326  {
327  if (TupleDescAttr(tupleDesc, i)->attlen == -1)
328  {
329  Datum value = values[i];
330 
331  if (isnull[i])
332  continue;
334  toast_delete_datum(rel, value, is_speculative);
335  }
336  }
337 }
#define VARATT_IS_EXTERNAL_ONDISK(PTR)
Definition: postgres.h:327
#define VARATT_IS_COMPRESSED(PTR)
Definition: postgres.h:325
Datum toast_compress_datum(Datum value, char cmethod)
static struct @142 value
#define TOASTCOL_INCOMPRESSIBLE
Definition: toast_helper.h:102
uint8 tai_colflags
Definition: toast_helper.h:34
#define TOASTCOL_NEEDS_DELETE_OLD
Definition: toast_helper.h:99
void toast_tuple_try_compression(ToastTupleContext *ttc, int attribute)
Definition: toast_helper.c:227
#define VARSIZE(PTR)
Definition: postgres.h:316
#define PointerGetDatum(X)
Definition: postgres.h:600
#define TupleDescAttr(tupdesc, i)
Definition: tupdesc.h:92
struct varlena * detoast_external_attr(struct varlena *attr)
Definition: detoast.c:45
signed int int32
Definition: c.h:429
#define TOAST_NEEDS_CHANGE
Definition: toast_helper.h:81
#define VARATT_IS_EXTERNAL(PTR)
Definition: postgres.h:326
struct varlena * detoast_attr(struct varlena *attr)
Definition: detoast.c:116
void pfree(void *pointer)
Definition: mcxt.c:1169
#define TOAST_NEEDS_FREE
Definition: toast_helper.h:79
char tai_compression
Definition: toast_helper.h:35
#define TOASTCOL_NEEDS_FREE
Definition: toast_helper.h:100
void toast_tuple_cleanup(ToastTupleContext *ttc)
Definition: toast_helper.c:275
int toast_tuple_find_biggest_attribute(ToastTupleContext *ttc, bool for_compression, bool check_main)
Definition: toast_helper.c:181
FormData_pg_attribute * Form_pg_attribute
Definition: pg_attribute.h:203
#define TOAST_POINTER_SIZE
Definition: detoast.h:31
void toast_delete_datum(Relation rel, Datum value, bool is_speculative)
void toast_delete_external(Relation rel, Datum *values, bool *isnull, bool is_speculative)
Definition: toast_helper.c:318
#define TOAST_HAS_NULLS
Definition: toast_helper.h:80
int16 attlen
Definition: pg_attribute.h:68
uintptr_t Datum
Definition: postgres.h:411
TupleDesc rd_att
Definition: rel.h:110
#define VARSIZE_ANY(PTR)
Definition: postgres.h:348
Datum * ttc_oldvalues
Definition: toast_helper.h:52
#define MAXALIGN(LEN)
Definition: c.h:757
#define DatumGetPointer(X)
Definition: postgres.h:593
static Datum values[MAXATTR]
Definition: bootstrap.c:166
#define TOAST_NEEDS_DELETE_OLD
Definition: toast_helper.h:78
int i
struct varlena * tai_oldexternal
Definition: toast_helper.h:32
Definition: c.h:621
#define TOASTCOL_IGNORE
Definition: toast_helper.h:101
Datum toast_save_datum(Relation rel, Datum value, struct varlena *oldexternal, int options)
ToastAttrInfo * ttc_attr
Definition: toast_helper.h:62
#define VARSIZE_EXTERNAL(PTR)
Definition: postgres.h:322
void toast_tuple_init(ToastTupleContext *ttc)
Definition: toast_helper.c:41
void toast_tuple_externalize(ToastTupleContext *ttc, int attribute, int options)
Definition: toast_helper.c:256