Age Owner Branch data TLA Line data Source code
1 : : /*-------------------------------------------------------------------------
2 : : *
3 : : * nbtdedup.c
4 : : * Deduplicate or bottom-up delete items in Postgres btrees.
5 : : *
6 : : * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
7 : : * Portions Copyright (c) 1994, Regents of the University of California
8 : : *
9 : : *
10 : : * IDENTIFICATION
11 : : * src/backend/access/nbtree/nbtdedup.c
12 : : *
13 : : *-------------------------------------------------------------------------
14 : : */
15 : : #include "postgres.h"
16 : :
17 : : #include "access/nbtree.h"
18 : : #include "access/nbtxlog.h"
19 : : #include "access/tableam.h"
20 : : #include "access/xloginsert.h"
21 : : #include "miscadmin.h"
22 : : #include "utils/rel.h"
23 : :
24 : : static void _bt_bottomupdel_finish_pending(Page page, BTDedupState state,
25 : : TM_IndexDeleteOp *delstate);
26 : : static bool _bt_do_singleval(Relation rel, Page page, BTDedupState state,
27 : : OffsetNumber minoff, IndexTuple newitem);
28 : : static void _bt_singleval_fillfactor(Page page, BTDedupState state,
29 : : Size newitemsz);
30 : : #ifdef USE_ASSERT_CHECKING
31 : : static bool _bt_posting_valid(IndexTuple posting);
32 : : #endif
33 : :
34 : : /*
35 : : * Perform a deduplication pass.
36 : : *
37 : : * The general approach taken here is to perform as much deduplication as
38 : : * possible to free as much space as possible. Note, however, that "single
39 : : * value" strategy is used for !bottomupdedup callers when the page is full of
40 : : * tuples of a single value. Deduplication passes that apply the strategy
41 : : * will leave behind a few untouched tuples at the end of the page, preparing
42 : : * the page for an anticipated page split that uses nbtsplitloc.c's own single
43 : : * value strategy. Our high level goal is to delay merging the untouched
44 : : * tuples until after the page splits.
45 : : *
46 : : * When a call to _bt_bottomupdel_pass() just took place (and failed), our
47 : : * high level goal is to prevent a page split entirely by buying more time.
48 : : * We still hope that a page split can be avoided altogether. That's why
49 : : * single value strategy is not even considered for bottomupdedup callers.
50 : : *
51 : : * The page will have to be split if we cannot successfully free at least
52 : : * newitemsz (we also need space for newitem's line pointer, which isn't
53 : : * included in caller's newitemsz).
54 : : *
55 : : * Note: Caller should have already deleted all existing items with their
56 : : * LP_DEAD bits set.
57 : : */
58 : : void
872 pg@bowt.ie 59 :CBC 13283 : _bt_dedup_pass(Relation rel, Buffer buf, IndexTuple newitem, Size newitemsz,
60 : : bool bottomupdedup)
61 : : {
62 : : OffsetNumber offnum,
63 : : minoff,
64 : : maxoff;
2019 65 : 13283 : Page page = BufferGetPage(buf);
1254 michael@paquier.xyz 66 : 13283 : BTPageOpaque opaque = BTPageGetOpaque(page);
67 : : Page newpage;
68 : : BTDedupState state;
1249 tgl@sss.pgh.pa.us 69 : 13283 : Size pagesaving PG_USED_FOR_ASSERTS_ONLY = 0;
2019 pg@bowt.ie 70 : 13283 : bool singlevalstrat = false;
1988 71 : 13283 : int nkeyatts = IndexRelationGetNumberOfKeyAttributes(rel);
72 : :
73 : : /* Passed-in newitemsz is MAXALIGNED but does not include line pointer */
2019 74 : 13283 : newitemsz += sizeof(ItemIdData);
75 : :
76 : : /*
77 : : * Initialize deduplication state.
78 : : *
79 : : * It would be possible for maxpostingsize (limit on posting list tuple
80 : : * size) to be set to one third of the page. However, it seems like a
81 : : * good idea to limit the size of posting lists to one sixth of a page.
82 : : * That ought to leave us with a good split point when pages full of
83 : : * duplicates can be split several times.
84 : : */
85 : 13283 : state = (BTDedupState) palloc(sizeof(BTDedupStateData));
86 : 13283 : state->deduplicate = true;
1905 87 : 13283 : state->nmaxitems = 0;
179 88 : 13283 : state->maxpostingsize = Min(BTMaxItemSize / 2, INDEX_SIZE_MASK);
89 : : /* Metadata about base tuple of current pending posting list */
2019 90 : 13283 : state->base = NULL;
91 : 13283 : state->baseoff = InvalidOffsetNumber;
92 : 13283 : state->basetupsize = 0;
93 : : /* Metadata about current pending posting list TIDs */
94 : 13283 : state->htids = palloc(state->maxpostingsize);
95 : 13283 : state->nhtids = 0;
96 : 13283 : state->nitems = 0;
97 : : /* Size of all physical tuples to be replaced by pending posting list */
98 : 13283 : state->phystupsize = 0;
99 : : /* nintervals should be initialized to zero */
100 : 13283 : state->nintervals = 0;
101 : :
1754 102 [ + + ]: 13283 : minoff = P_FIRSTDATAKEY(opaque);
103 : 13283 : maxoff = PageGetMaxOffsetNumber(page);
104 : :
105 : : /*
106 : : * Consider applying "single value" strategy, though only if the page
107 : : * seems likely to be split in the near future
108 : : */
1446 109 [ + + ]: 13283 : if (!bottomupdedup)
2019 110 : 11561 : singlevalstrat = _bt_do_singleval(rel, page, state, minoff, newitem);
111 : :
112 : : /*
113 : : * Deduplicate items from page, and write them to newpage.
114 : : *
115 : : * Copy the original page's LSN into newpage copy. This will become the
116 : : * updated version of the page. We need this because XLogInsert will
117 : : * examine the LSN and possibly dump it in a page image.
118 : : */
119 : 13283 : newpage = PageGetTempPageCopySpecial(page);
120 : 13283 : PageSetLSN(newpage, PageGetLSN(page));
121 : :
122 : : /* Copy high key, if any */
123 [ + + ]: 13283 : if (!P_RIGHTMOST(opaque))
124 : : {
125 : 10508 : ItemId hitemid = PageGetItemId(page, P_HIKEY);
126 : 10508 : Size hitemsz = ItemIdGetLength(hitemid);
127 : 10508 : IndexTuple hitem = (IndexTuple) PageGetItem(page, hitemid);
128 : :
129 [ - + ]: 10508 : if (PageAddItem(newpage, (Item) hitem, hitemsz, P_HIKEY,
130 : : false, false) == InvalidOffsetNumber)
2019 pg@bowt.ie 131 [ # # ]:UBC 0 : elog(ERROR, "deduplication failed to add highkey");
132 : : }
133 : :
2019 pg@bowt.ie 134 :CBC 13283 : for (offnum = minoff;
135 [ + + ]: 2984592 : offnum <= maxoff;
136 : 2971309 : offnum = OffsetNumberNext(offnum))
137 : : {
138 : 2971309 : ItemId itemid = PageGetItemId(page, offnum);
139 : 2971309 : IndexTuple itup = (IndexTuple) PageGetItem(page, itemid);
140 : :
141 [ - + ]: 2971309 : Assert(!ItemIdIsDead(itemid));
142 : :
143 [ + + ]: 2971309 : if (offnum == minoff)
144 : : {
145 : : /*
146 : : * No previous/base tuple for the data item -- use the data item
147 : : * as base tuple of pending posting list
148 : : */
149 : 13283 : _bt_dedup_start_pending(state, itup, offnum);
150 : : }
151 [ + + + + ]: 5914926 : else if (state->deduplicate &&
1988 152 [ + + ]: 3370534 : _bt_keep_natts_fast(rel, state->base, itup) > nkeyatts &&
2019 153 : 413634 : _bt_dedup_save_htid(state, itup))
154 : : {
155 : : /*
156 : : * Tuple is equal to base tuple of pending posting list. Heap
157 : : * TID(s) for itup have been saved in state.
158 : : */
159 : : }
160 : : else
161 : : {
162 : : /*
163 : : * Tuple is not equal to pending posting list tuple, or
164 : : * _bt_dedup_save_htid() opted to not merge current item into
165 : : * pending posting list for some other reason (e.g., adding more
166 : : * TIDs would have caused posting list to exceed current
167 : : * maxpostingsize).
168 : : *
169 : : * If state contains pending posting list with more than one item,
170 : : * form new posting tuple and add it to our temp page (newpage).
171 : : * Else add pending interval's base tuple to the temp page as-is.
172 : : */
173 : 2550766 : pagesaving += _bt_dedup_finish_pending(newpage, state);
174 : :
175 [ + + ]: 2550766 : if (singlevalstrat)
176 : : {
177 : : /*
178 : : * Single value strategy's extra steps.
179 : : *
180 : : * Lower maxpostingsize for sixth and final large posting list
181 : : * tuple at the point where 5 maxpostingsize-capped tuples
182 : : * have either been formed or observed.
183 : : *
184 : : * When a sixth maxpostingsize-capped item is formed/observed,
185 : : * stop merging together tuples altogether. The few tuples
186 : : * that remain at the end of the page won't be merged together
187 : : * at all (at least not until after a future page split takes
188 : : * place, when this page's newly allocated right sibling page
189 : : * gets its first deduplication pass).
190 : : */
1905 191 [ + + ]: 2674 : if (state->nmaxitems == 5)
2019 192 : 326 : _bt_singleval_fillfactor(page, state, newitemsz);
1905 193 [ + + ]: 2348 : else if (state->nmaxitems == 6)
194 : : {
2019 195 : 127 : state->deduplicate = false;
196 : 127 : singlevalstrat = false; /* won't be back here */
197 : : }
198 : : }
199 : :
200 : : /* itup starts new pending posting list */
201 : 2550766 : _bt_dedup_start_pending(state, itup, offnum);
202 : : }
203 : : }
204 : :
205 : : /* Handle the last item */
206 : 13283 : pagesaving += _bt_dedup_finish_pending(newpage, state);
207 : :
208 : : /*
209 : : * If no items suitable for deduplication were found, newpage must be
210 : : * exactly the same as the original page, so just return from function.
211 : : *
212 : : * We could determine whether or not to proceed on the basis the space
213 : : * savings being sufficient to avoid an immediate page split instead. We
214 : : * don't do that because there is some small value in nbtsplitloc.c always
215 : : * operating against a page that is fully deduplicated (apart from
216 : : * newitem). Besides, most of the cost has already been paid.
217 : : */
218 [ + + ]: 13283 : if (state->nintervals == 0)
219 : : {
220 : : /* cannot leak memory here */
221 : 2303 : pfree(newpage);
222 : 2303 : pfree(state->htids);
223 : 2303 : pfree(state);
224 : 2303 : return;
225 : : }
226 : :
227 : : /*
228 : : * By here, it's clear that deduplication will definitely go ahead.
229 : : *
230 : : * Clear the BTP_HAS_GARBAGE page flag. The index must be a heapkeyspace
231 : : * index, and as such we'll never pay attention to BTP_HAS_GARBAGE anyway.
232 : : * But keep things tidy.
233 : : */
234 [ - + ]: 10980 : if (P_HAS_GARBAGE(opaque))
235 : : {
1254 michael@paquier.xyz 236 :UBC 0 : BTPageOpaque nopaque = BTPageGetOpaque(newpage);
237 : :
2019 pg@bowt.ie 238 : 0 : nopaque->btpo_flags &= ~BTP_HAS_GARBAGE;
239 : : }
240 : :
2019 pg@bowt.ie 241 :CBC 10980 : START_CRIT_SECTION();
242 : :
243 : 10980 : PageRestoreTempPage(newpage, page);
244 : 10980 : MarkBufferDirty(buf);
245 : :
246 : : /* XLOG stuff */
247 [ + + + + : 10980 : if (RelationNeedsWAL(rel))
+ - + - ]
248 : : {
249 : : XLogRecPtr recptr;
250 : : xl_btree_dedup xlrec_dedup;
251 : :
252 : 10917 : xlrec_dedup.nintervals = state->nintervals;
253 : :
254 : 10917 : XLogBeginInsert();
255 : 10917 : XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
207 peter@eisentraut.org 256 : 10917 : XLogRegisterData(&xlrec_dedup, SizeOfBtreeDedup);
257 : :
258 : : /*
259 : : * The intervals array is not in the buffer, but pretend that it is.
260 : : * When XLogInsert stores the whole buffer, the array need not be
261 : : * stored too.
262 : : */
263 : 10917 : XLogRegisterBufData(0, state->intervals,
2019 pg@bowt.ie 264 : 10917 : state->nintervals * sizeof(BTDedupInterval));
265 : :
266 : 10917 : recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_DEDUP);
267 : :
268 : 10917 : PageSetLSN(page, recptr);
269 : : }
270 : :
271 [ - + ]: 10980 : END_CRIT_SECTION();
272 : :
273 : : /* Local space accounting should agree with page accounting */
274 [ + + - + ]: 10980 : Assert(pagesaving < newitemsz || PageGetExactFreeSpace(page) >= newitemsz);
275 : :
276 : : /* cannot leak memory here */
277 : 10980 : pfree(state->htids);
278 : 10980 : pfree(state);
279 : : }
280 : :
281 : : /*
282 : : * Perform bottom-up index deletion pass.
283 : : *
284 : : * See if duplicate index tuples (plus certain nearby tuples) are eligible to
285 : : * be deleted via bottom-up index deletion. The high level goal here is to
286 : : * entirely prevent "unnecessary" page splits caused by MVCC version churn
287 : : * from UPDATEs (when the UPDATEs don't logically modify any of the columns
288 : : * covered by the 'rel' index). This is qualitative, not quantitative -- we
289 : : * do not particularly care about once-off opportunities to delete many index
290 : : * tuples together.
291 : : *
292 : : * See nbtree/README for details on the design of nbtree bottom-up deletion.
293 : : * See access/tableam.h for a description of how we're expected to cooperate
294 : : * with the tableam.
295 : : *
296 : : * Returns true on success, in which case caller can assume page split will be
297 : : * avoided for a reasonable amount of time. Returns false when caller should
298 : : * deduplicate the page (if possible at all).
299 : : *
300 : : * Note: Occasionally we return true despite failing to delete enough items to
301 : : * avoid a split. This makes caller skip deduplication and go split the page
302 : : * right away. Our return value is always just advisory information.
303 : : *
304 : : * Note: Caller should have already deleted all existing items with their
305 : : * LP_DEAD bits set.
306 : : */
307 : : bool
1697 308 : 1930 : _bt_bottomupdel_pass(Relation rel, Buffer buf, Relation heapRel,
309 : : Size newitemsz)
310 : : {
311 : : OffsetNumber offnum,
312 : : minoff,
313 : : maxoff;
314 : 1930 : Page page = BufferGetPage(buf);
1254 michael@paquier.xyz 315 : 1930 : BTPageOpaque opaque = BTPageGetOpaque(page);
316 : : BTDedupState state;
317 : : TM_IndexDeleteOp delstate;
318 : : bool neverdedup;
1697 pg@bowt.ie 319 : 1930 : int nkeyatts = IndexRelationGetNumberOfKeyAttributes(rel);
320 : :
321 : : /* Passed-in newitemsz is MAXALIGNED but does not include line pointer */
322 : 1930 : newitemsz += sizeof(ItemIdData);
323 : :
324 : : /* Initialize deduplication state */
325 : 1930 : state = (BTDedupState) palloc(sizeof(BTDedupStateData));
326 : 1930 : state->deduplicate = true;
327 : 1930 : state->nmaxitems = 0;
328 : 1930 : state->maxpostingsize = BLCKSZ; /* We're not really deduplicating */
329 : 1930 : state->base = NULL;
330 : 1930 : state->baseoff = InvalidOffsetNumber;
331 : 1930 : state->basetupsize = 0;
332 : 1930 : state->htids = palloc(state->maxpostingsize);
333 : 1930 : state->nhtids = 0;
334 : 1930 : state->nitems = 0;
335 : 1930 : state->phystupsize = 0;
336 : 1930 : state->nintervals = 0;
337 : :
338 : : /*
339 : : * Initialize tableam state that describes bottom-up index deletion
340 : : * operation.
341 : : *
342 : : * We'll go on to ask the tableam to search for TIDs whose index tuples we
343 : : * can safely delete. The tableam will search until our leaf page space
344 : : * target is satisfied, or until the cost of continuing with the tableam
345 : : * operation seems too high. It focuses its efforts on TIDs associated
346 : : * with duplicate index tuples that we mark "promising".
347 : : *
348 : : * This space target is a little arbitrary. The tableam must be able to
349 : : * keep the costs and benefits in balance. We provide the tableam with
350 : : * exhaustive information about what might work, without directly
351 : : * concerning ourselves with avoiding work during the tableam call. Our
352 : : * role in costing the bottom-up deletion process is strictly advisory.
353 : : */
1402 354 : 1930 : delstate.irel = rel;
355 : 1930 : delstate.iblknum = BufferGetBlockNumber(buf);
1697 356 : 1930 : delstate.bottomup = true;
357 : 1930 : delstate.bottomupfreespace = Max(BLCKSZ / 16, newitemsz);
358 : 1930 : delstate.ndeltids = 0;
359 : 1930 : delstate.deltids = palloc(MaxTIDsPerBTreePage * sizeof(TM_IndexDelete));
360 : 1930 : delstate.status = palloc(MaxTIDsPerBTreePage * sizeof(TM_IndexStatus));
361 : :
362 [ + + ]: 1930 : minoff = P_FIRSTDATAKEY(opaque);
363 : 1930 : maxoff = PageGetMaxOffsetNumber(page);
364 : 1930 : for (offnum = minoff;
365 [ + + ]: 530851 : offnum <= maxoff;
366 : 528921 : offnum = OffsetNumberNext(offnum))
367 : : {
368 : 528921 : ItemId itemid = PageGetItemId(page, offnum);
369 : 528921 : IndexTuple itup = (IndexTuple) PageGetItem(page, itemid);
370 : :
371 [ - + ]: 528921 : Assert(!ItemIdIsDead(itemid));
372 : :
373 [ + + ]: 528921 : if (offnum == minoff)
374 : : {
375 : : /* itup starts first pending interval */
376 : 1930 : _bt_dedup_start_pending(state, itup, offnum);
377 : : }
378 [ + + + - ]: 601309 : else if (_bt_keep_natts_fast(rel, state->base, itup) > nkeyatts &&
379 : 74318 : _bt_dedup_save_htid(state, itup))
380 : : {
381 : : /* Tuple is equal; just added its TIDs to pending interval */
382 : : }
383 : : else
384 : : {
385 : : /* Finalize interval -- move its TIDs to delete state */
386 : 452673 : _bt_bottomupdel_finish_pending(page, state, &delstate);
387 : :
388 : : /* itup starts new pending interval */
389 : 452673 : _bt_dedup_start_pending(state, itup, offnum);
390 : : }
391 : : }
392 : : /* Finalize final interval -- move its TIDs to delete state */
393 : 1930 : _bt_bottomupdel_finish_pending(page, state, &delstate);
394 : :
395 : : /*
396 : : * We don't give up now in the event of having few (or even zero)
397 : : * promising tuples for the tableam because it's not up to us as the index
398 : : * AM to manage costs (note that the tableam might have heuristics of its
399 : : * own that work out what to do). We should at least avoid having our
400 : : * caller do a useless deduplication pass after we return in the event of
401 : : * zero promising tuples, though.
402 : : */
403 : 1930 : neverdedup = false;
404 [ + + ]: 1930 : if (state->nintervals == 0)
405 : 4 : neverdedup = true;
406 : :
407 : 1930 : pfree(state->htids);
408 : 1930 : pfree(state);
409 : :
410 : : /* Ask tableam which TIDs are deletable, then physically delete them */
411 : 1930 : _bt_delitems_delete_check(rel, buf, heapRel, &delstate);
412 : :
413 : 1930 : pfree(delstate.deltids);
414 : 1930 : pfree(delstate.status);
415 : :
416 : : /* Report "success" to caller unconditionally to avoid deduplication */
417 [ + + ]: 1930 : if (neverdedup)
418 : 4 : return true;
419 : :
420 : : /* Don't dedup when we won't end up back here any time soon anyway */
421 : 1926 : return PageGetExactFreeSpace(page) >= Max(BLCKSZ / 24, newitemsz);
422 : : }
423 : :
424 : : /*
425 : : * Create a new pending posting list tuple based on caller's base tuple.
426 : : *
427 : : * Every tuple processed by deduplication either becomes the base tuple for a
428 : : * posting list, or gets its heap TID(s) accepted into a pending posting list.
429 : : * A tuple that starts out as the base tuple for a posting list will only
430 : : * actually be rewritten within _bt_dedup_finish_pending() when it turns out
431 : : * that there are duplicates that can be merged into the base tuple.
432 : : */
433 : : void
2019 434 : 5790210 : _bt_dedup_start_pending(BTDedupState state, IndexTuple base,
435 : : OffsetNumber baseoff)
436 : : {
437 [ - + ]: 5790210 : Assert(state->nhtids == 0);
438 [ - + ]: 5790210 : Assert(state->nitems == 0);
439 [ - + ]: 5790210 : Assert(!BTreeTupleIsPivot(base));
440 : :
441 : : /*
442 : : * Copy heap TID(s) from new base tuple for new candidate posting list
443 : : * into working state's array
444 : : */
445 [ + + ]: 5790210 : if (!BTreeTupleIsPosting(base))
446 : : {
447 : 4841822 : memcpy(state->htids, &base->t_tid, sizeof(ItemPointerData));
448 : 4841822 : state->nhtids = 1;
449 : 4841822 : state->basetupsize = IndexTupleSize(base);
450 : : }
451 : : else
452 : : {
453 : : int nposting;
454 : :
455 : 948388 : nposting = BTreeTupleGetNPosting(base);
456 : 948388 : memcpy(state->htids, BTreeTupleGetPosting(base),
457 : : sizeof(ItemPointerData) * nposting);
458 : 948388 : state->nhtids = nposting;
459 : : /* basetupsize should not include existing posting list */
460 : 948388 : state->basetupsize = BTreeTupleGetPostingOffset(base);
461 : : }
462 : :
463 : : /*
464 : : * Save new base tuple itself -- it'll be needed if we actually create a
465 : : * new posting list from new pending posting list.
466 : : *
467 : : * Must maintain physical size of all existing tuples (including line
468 : : * pointer overhead) so that we can calculate space savings on page.
469 : : */
470 : 5790210 : state->nitems = 1;
471 : 5790210 : state->base = base;
472 : 5790210 : state->baseoff = baseoff;
473 : 5790210 : state->phystupsize = MAXALIGN(IndexTupleSize(base)) + sizeof(ItemIdData);
474 : : /* Also save baseoff in pending state for interval */
475 : 5790210 : state->intervals[state->nintervals].baseoff = state->baseoff;
476 : 5790210 : }
477 : :
478 : : /*
479 : : * Save itup heap TID(s) into pending posting list where possible.
480 : : *
481 : : * Returns bool indicating if the pending posting list managed by state now
482 : : * includes itup's heap TID(s).
483 : : */
484 : : bool
485 : 1254475 : _bt_dedup_save_htid(BTDedupState state, IndexTuple itup)
486 : : {
487 : : int nhtids;
488 : : ItemPointer htids;
489 : : Size mergedtupsz;
490 : :
491 [ - + ]: 1254475 : Assert(!BTreeTupleIsPivot(itup));
492 : :
493 [ + + ]: 1254475 : if (!BTreeTupleIsPosting(itup))
494 : : {
495 : 1248115 : nhtids = 1;
496 : 1248115 : htids = &itup->t_tid;
497 : : }
498 : : else
499 : : {
500 : 6360 : nhtids = BTreeTupleGetNPosting(itup);
501 : 6360 : htids = BTreeTupleGetPosting(itup);
502 : : }
503 : :
504 : : /*
505 : : * Don't append (have caller finish pending posting list as-is) if
506 : : * appending heap TID(s) from itup would put us over maxpostingsize limit.
507 : : *
508 : : * This calculation needs to match the code used within _bt_form_posting()
509 : : * for new posting list tuples.
510 : : */
511 : 1254475 : mergedtupsz = MAXALIGN(state->basetupsize +
512 : : (state->nhtids + nhtids) * sizeof(ItemPointerData));
513 : :
514 [ + + ]: 1254475 : if (mergedtupsz > state->maxpostingsize)
515 : : {
516 : : /*
517 : : * Count this as an oversized item for single value strategy, though
518 : : * only when there are 50 TIDs in the final posting list tuple. This
519 : : * limit (which is fairly arbitrary) avoids confusion about how many
520 : : * 1/6 of a page tuples have been encountered/created by the current
521 : : * deduplication pass.
522 : : *
523 : : * Note: We deliberately don't consider which deduplication pass
524 : : * merged together tuples to create this item (could be a previous
525 : : * deduplication pass, or current pass). See _bt_do_singleval()
526 : : * comments.
527 : : */
1905 528 [ + + ]: 10297 : if (state->nhtids > 50)
529 : 9685 : state->nmaxitems++;
530 : :
2019 531 : 10297 : return false;
532 : : }
533 : :
534 : : /*
535 : : * Save heap TIDs to pending posting list tuple -- itup can be merged into
536 : : * pending posting list
537 : : */
538 : 1244178 : state->nitems++;
539 : 1244178 : memcpy(state->htids + state->nhtids, htids,
540 : : sizeof(ItemPointerData) * nhtids);
541 : 1244178 : state->nhtids += nhtids;
542 : 1244178 : state->phystupsize += MAXALIGN(IndexTupleSize(itup)) + sizeof(ItemIdData);
543 : :
544 : 1244178 : return true;
545 : : }
546 : :
547 : : /*
548 : : * Finalize pending posting list tuple, and add it to the page. Final tuple
549 : : * is based on saved base tuple, and saved list of heap TIDs.
550 : : *
551 : : * Returns space saving from deduplicating to make a new posting list tuple.
552 : : * Note that this includes line pointer overhead. This is zero in the case
553 : : * where no deduplication was possible.
554 : : */
555 : : Size
556 : 2976729 : _bt_dedup_finish_pending(Page newpage, BTDedupState state)
557 : : {
558 : : OffsetNumber tupoff;
559 : : Size tuplesz;
560 : : Size spacesaving;
561 : :
562 [ - + ]: 2976729 : Assert(state->nitems > 0);
563 [ - + ]: 2976729 : Assert(state->nitems <= state->nhtids);
564 [ - + ]: 2976729 : Assert(state->intervals[state->nintervals].baseoff == state->baseoff);
565 : :
566 : 2976729 : tupoff = OffsetNumberNext(PageGetMaxOffsetNumber(newpage));
567 [ + + ]: 2976729 : if (state->nitems == 1)
568 : : {
569 : : /* Use original, unchanged base tuple */
570 : 2775542 : tuplesz = IndexTupleSize(state->base);
1128 571 [ - + ]: 2775542 : Assert(tuplesz == MAXALIGN(IndexTupleSize(state->base)));
179 572 [ - + ]: 2775542 : Assert(tuplesz <= BTMaxItemSize);
2019 573 [ - + ]: 2775542 : if (PageAddItem(newpage, (Item) state->base, tuplesz, tupoff,
574 : : false, false) == InvalidOffsetNumber)
2019 pg@bowt.ie 575 [ # # ]:UBC 0 : elog(ERROR, "deduplication failed to add tuple to page");
576 : :
2019 pg@bowt.ie 577 :CBC 2775542 : spacesaving = 0;
578 : : }
579 : : else
580 : : {
581 : : IndexTuple final;
582 : :
583 : : /* Form a tuple with a posting list */
584 : 201187 : final = _bt_form_posting(state->base, state->htids, state->nhtids);
585 : 201187 : tuplesz = IndexTupleSize(final);
586 [ - + ]: 201187 : Assert(tuplesz <= state->maxpostingsize);
587 : :
588 : : /* Save final number of items for posting list */
589 : 201187 : state->intervals[state->nintervals].nitems = state->nitems;
590 : :
591 [ - + ]: 201187 : Assert(tuplesz == MAXALIGN(IndexTupleSize(final)));
179 592 [ - + ]: 201187 : Assert(tuplesz <= BTMaxItemSize);
2019 593 [ - + ]: 201187 : if (PageAddItem(newpage, (Item) final, tuplesz, tupoff, false,
594 : : false) == InvalidOffsetNumber)
2019 pg@bowt.ie 595 [ # # ]:UBC 0 : elog(ERROR, "deduplication failed to add tuple to page");
596 : :
2019 pg@bowt.ie 597 :CBC 201187 : pfree(final);
598 : 201187 : spacesaving = state->phystupsize - (tuplesz + sizeof(ItemIdData));
599 : : /* Increment nintervals, since we wrote a new posting list tuple */
600 : 201187 : state->nintervals++;
601 [ + - - + ]: 201187 : Assert(spacesaving > 0 && spacesaving < BLCKSZ);
602 : : }
603 : :
604 : : /* Reset state for next pending posting list */
605 : 2976729 : state->nhtids = 0;
606 : 2976729 : state->nitems = 0;
607 : 2976729 : state->phystupsize = 0;
608 : :
609 : 2976729 : return spacesaving;
610 : : }
611 : :
612 : : /*
613 : : * Finalize interval during bottom-up index deletion.
614 : : *
615 : : * During a bottom-up pass we expect that TIDs will be recorded in dedup state
616 : : * first, and then get moved over to delstate (in variable-sized batches) by
617 : : * calling here. Call here happens when the number of TIDs in a dedup
618 : : * interval is known, and interval gets finalized (i.e. when caller sees next
619 : : * tuple on the page is not a duplicate, or when caller runs out of tuples to
620 : : * process from leaf page).
621 : : *
622 : : * This is where bottom-up deletion determines and remembers which entries are
623 : : * duplicates. This will be important information to the tableam delete
624 : : * infrastructure later on. Plain index tuple duplicates are marked
625 : : * "promising" here, per tableam contract.
626 : : *
627 : : * Our approach to marking entries whose TIDs come from posting lists is more
628 : : * complicated. Posting lists can only be formed by a deduplication pass (or
629 : : * during an index build), so recent version churn affecting the pointed-to
630 : : * logical rows is not particularly likely. We may still give a weak signal
631 : : * about posting list tuples' entries (by marking just one of its TIDs/entries
632 : : * promising), though this is only a possibility in the event of further
633 : : * duplicate index tuples in final interval that covers posting list tuple (as
634 : : * in the plain tuple case). A weak signal/hint will be useful to the tableam
635 : : * when it has no stronger signal to go with for the deletion operation as a
636 : : * whole.
637 : : *
638 : : * The heuristics we use work well in practice because we only need to give
639 : : * the tableam the right _general_ idea about where to look. Garbage tends to
640 : : * naturally get concentrated in relatively few table blocks with workloads
641 : : * that bottom-up deletion targets. The tableam cannot possibly rank all
642 : : * available table blocks sensibly based on the hints we provide, but that's
643 : : * okay -- only the extremes matter. The tableam just needs to be able to
644 : : * predict which few table blocks will have the most tuples that are safe to
645 : : * delete for each deletion operation, with low variance across related
646 : : * deletion operations.
647 : : */
648 : : static void
1697 649 : 454603 : _bt_bottomupdel_finish_pending(Page page, BTDedupState state,
650 : : TM_IndexDeleteOp *delstate)
651 : : {
652 : 454603 : bool dupinterval = (state->nitems > 1);
653 : :
654 [ - + ]: 454603 : Assert(state->nitems > 0);
655 [ - + ]: 454603 : Assert(state->nitems <= state->nhtids);
656 [ - + ]: 454603 : Assert(state->intervals[state->nintervals].baseoff == state->baseoff);
657 : :
658 [ + + ]: 983524 : for (int i = 0; i < state->nitems; i++)
659 : : {
660 : 528921 : OffsetNumber offnum = state->baseoff + i;
661 : 528921 : ItemId itemid = PageGetItemId(page, offnum);
662 : 528921 : IndexTuple itup = (IndexTuple) PageGetItem(page, itemid);
663 : 528921 : TM_IndexDelete *ideltid = &delstate->deltids[delstate->ndeltids];
664 : 528921 : TM_IndexStatus *istatus = &delstate->status[delstate->ndeltids];
665 : :
666 [ + + ]: 528921 : if (!BTreeTupleIsPosting(itup))
667 : : {
668 : : /* Simple case: A plain non-pivot tuple */
669 : 422665 : ideltid->tid = itup->t_tid;
670 : 422665 : ideltid->id = delstate->ndeltids;
671 : 422665 : istatus->idxoffnum = offnum;
672 : 422665 : istatus->knowndeletable = false; /* for now */
673 : 422665 : istatus->promising = dupinterval; /* simple rule */
674 : 422665 : istatus->freespace = ItemIdGetLength(itemid) + sizeof(ItemIdData);
675 : :
676 : 422665 : delstate->ndeltids++;
677 : : }
678 : : else
679 : : {
680 : : /*
681 : : * Complicated case: A posting list tuple.
682 : : *
683 : : * We make the conservative assumption that there can only be at
684 : : * most one affected logical row per posting list tuple. There
685 : : * will be at most one promising entry in deltids to represent
686 : : * this presumed lone logical row. Note that this isn't even
687 : : * considered unless the posting list tuple is also in an interval
688 : : * of duplicates -- this complicated rule is just a variant of the
689 : : * simple rule used to decide if plain index tuples are promising.
690 : : */
691 : 106256 : int nitem = BTreeTupleGetNPosting(itup);
692 : 106256 : bool firstpromising = false;
693 : 106256 : bool lastpromising = false;
694 : :
695 [ - + ]: 106256 : Assert(_bt_posting_valid(itup));
696 : :
697 [ + + ]: 106256 : if (dupinterval)
698 : : {
699 : : /*
700 : : * Complicated rule: either the first or last TID in the
701 : : * posting list gets marked promising (if any at all)
702 : : */
703 : : BlockNumber minblocklist,
704 : : midblocklist,
705 : : maxblocklist;
706 : : ItemPointer mintid,
707 : : midtid,
708 : : maxtid;
709 : :
710 : 8535 : mintid = BTreeTupleGetHeapTID(itup);
711 : 8535 : midtid = BTreeTupleGetPostingN(itup, nitem / 2);
712 : 8535 : maxtid = BTreeTupleGetMaxHeapTID(itup);
713 : 8535 : minblocklist = ItemPointerGetBlockNumber(mintid);
714 : 8535 : midblocklist = ItemPointerGetBlockNumber(midtid);
715 : 8535 : maxblocklist = ItemPointerGetBlockNumber(maxtid);
716 : :
717 : : /* Only entry with predominant table block can be promising */
718 : 8535 : firstpromising = (minblocklist == midblocklist);
719 [ + + + + ]: 8535 : lastpromising = (!firstpromising &&
720 : : midblocklist == maxblocklist);
721 : : }
722 : :
723 [ + + ]: 592174 : for (int p = 0; p < nitem; p++)
724 : : {
725 : 485918 : ItemPointer htid = BTreeTupleGetPostingN(itup, p);
726 : :
727 : 485918 : ideltid->tid = *htid;
728 : 485918 : ideltid->id = delstate->ndeltids;
729 : 485918 : istatus->idxoffnum = offnum;
730 : 485918 : istatus->knowndeletable = false; /* for now */
731 : 485918 : istatus->promising = false;
732 [ + + + + : 485918 : if ((firstpromising && p == 0) ||
+ + ]
733 [ + + ]: 61888 : (lastpromising && p == nitem - 1))
734 : 5804 : istatus->promising = true;
735 : 485918 : istatus->freespace = sizeof(ItemPointerData); /* at worst */
736 : :
737 : 485918 : ideltid++;
738 : 485918 : istatus++;
739 : 485918 : delstate->ndeltids++;
740 : : }
741 : : }
742 : : }
743 : :
744 [ + + ]: 454603 : if (dupinterval)
745 : : {
746 : 49281 : state->intervals[state->nintervals].nitems = state->nitems;
747 : 49281 : state->nintervals++;
748 : : }
749 : :
750 : : /* Reset state for next interval */
751 : 454603 : state->nhtids = 0;
752 : 454603 : state->nitems = 0;
753 : 454603 : state->phystupsize = 0;
754 : 454603 : }
755 : :
756 : : /*
757 : : * Determine if page non-pivot tuples (data items) are all duplicates of the
758 : : * same value -- if they are, deduplication's "single value" strategy should
759 : : * be applied. The general goal of this strategy is to ensure that
760 : : * nbtsplitloc.c (which uses its own single value strategy) will find a useful
761 : : * split point as further duplicates are inserted, and successive rightmost
762 : : * page splits occur among pages that store the same duplicate value. When
763 : : * the page finally splits, it should end up BTREE_SINGLEVAL_FILLFACTOR% full,
764 : : * just like it would if deduplication were disabled.
765 : : *
766 : : * We expect that affected workloads will require _several_ single value
767 : : * strategy deduplication passes (over a page that only stores duplicates)
768 : : * before the page is finally split. The first deduplication pass should only
769 : : * find regular non-pivot tuples. Later deduplication passes will find
770 : : * existing maxpostingsize-capped posting list tuples, which must be skipped
771 : : * over. The penultimate pass is generally the first pass that actually
772 : : * reaches _bt_singleval_fillfactor(), and so will deliberately leave behind a
773 : : * few untouched non-pivot tuples. The final deduplication pass won't free
774 : : * any space -- it will skip over everything without merging anything (it
775 : : * retraces the steps of the penultimate pass).
776 : : *
777 : : * Fortunately, having several passes isn't too expensive. Each pass (after
778 : : * the first pass) won't spend many cycles on the large posting list tuples
779 : : * left by previous passes. Each pass will find a large contiguous group of
780 : : * smaller duplicate tuples to merge together at the end of the page.
781 : : */
782 : : static bool
2019 783 : 11561 : _bt_do_singleval(Relation rel, Page page, BTDedupState state,
784 : : OffsetNumber minoff, IndexTuple newitem)
785 : : {
1988 786 : 11561 : int nkeyatts = IndexRelationGetNumberOfKeyAttributes(rel);
787 : : ItemId itemid;
788 : : IndexTuple itup;
789 : :
2019 790 : 11561 : itemid = PageGetItemId(page, minoff);
791 : 11561 : itup = (IndexTuple) PageGetItem(page, itemid);
792 : :
1988 793 [ + + ]: 11561 : if (_bt_keep_natts_fast(rel, newitem, itup) > nkeyatts)
794 : : {
2019 795 : 1021 : itemid = PageGetItemId(page, PageGetMaxOffsetNumber(page));
796 : 1021 : itup = (IndexTuple) PageGetItem(page, itemid);
797 : :
1988 798 [ + + ]: 1021 : if (_bt_keep_natts_fast(rel, newitem, itup) > nkeyatts)
2019 799 : 664 : return true;
800 : : }
801 : :
802 : 10897 : return false;
803 : : }
804 : :
805 : : /*
806 : : * Lower maxpostingsize when using "single value" strategy, to avoid a sixth
807 : : * and final maxpostingsize-capped tuple. The sixth and final posting list
808 : : * tuple will end up somewhat smaller than the first five. (Note: The first
809 : : * five tuples could actually just be very large duplicate tuples that
810 : : * couldn't be merged together at all. Deduplication will simply not modify
811 : : * the page when that happens.)
812 : : *
813 : : * When there are six posting lists on the page (after current deduplication
814 : : * pass goes on to create/observe a sixth very large tuple), caller should end
815 : : * its deduplication pass. It isn't useful to try to deduplicate items that
816 : : * are supposed to end up on the new right sibling page following the
817 : : * anticipated page split. A future deduplication pass of future right
818 : : * sibling page might take care of it. (This is why the first single value
819 : : * strategy deduplication pass for a given leaf page will generally find only
820 : : * plain non-pivot tuples -- see _bt_do_singleval() comments.)
821 : : */
822 : : static void
823 : 326 : _bt_singleval_fillfactor(Page page, BTDedupState state, Size newitemsz)
824 : : {
825 : : Size leftfree;
826 : : int reduction;
827 : :
828 : : /* This calculation needs to match nbtsplitloc.c */
829 : 326 : leftfree = PageGetPageSize(page) - SizeOfPageHeaderData -
830 : : MAXALIGN(sizeof(BTPageOpaqueData));
831 : : /* Subtract size of new high key (includes pivot heap TID space) */
832 : 326 : leftfree -= newitemsz + MAXALIGN(sizeof(ItemPointerData));
833 : :
834 : : /*
835 : : * Reduce maxpostingsize by an amount equal to target free space on left
836 : : * half of page
837 : : */
838 : 326 : reduction = leftfree * ((100 - BTREE_SINGLEVAL_FILLFACTOR) / 100.0);
839 [ + - ]: 326 : if (state->maxpostingsize > reduction)
840 : 326 : state->maxpostingsize -= reduction;
841 : : else
2019 pg@bowt.ie 842 :UBC 0 : state->maxpostingsize = 0;
2019 pg@bowt.ie 843 :CBC 326 : }
844 : :
845 : : /*
846 : : * Build a posting list tuple based on caller's "base" index tuple and list of
847 : : * heap TIDs. When nhtids == 1, builds a standard non-pivot tuple without a
848 : : * posting list. (Posting list tuples can never have a single heap TID, partly
849 : : * because that ensures that deduplication always reduces final MAXALIGN()'d
850 : : * size of entire tuple.)
851 : : *
852 : : * Convention is that posting list starts at a MAXALIGN()'d offset (rather
853 : : * than a SHORTALIGN()'d offset), in line with the approach taken when
854 : : * appending a heap TID to new pivot tuple/high key during suffix truncation.
855 : : * This sometimes wastes a little space that was only needed as alignment
856 : : * padding in the original tuple. Following this convention simplifies the
857 : : * space accounting used when deduplicating a page (the same convention
858 : : * simplifies the accounting for choosing a point to split a page at).
859 : : *
860 : : * Note: Caller's "htids" array must be unique and already in ascending TID
861 : : * order. Any existing heap TIDs from "base" won't automatically appear in
862 : : * returned posting list tuple (they must be included in htids array.)
863 : : */
864 : : IndexTuple
865 : 246742 : _bt_form_posting(IndexTuple base, ItemPointer htids, int nhtids)
866 : : {
867 : : uint32 keysize,
868 : : newsize;
869 : : IndexTuple itup;
870 : :
871 [ + + ]: 246742 : if (BTreeTupleIsPosting(base))
872 : 66861 : keysize = BTreeTupleGetPostingOffset(base);
873 : : else
874 : 179881 : keysize = IndexTupleSize(base);
875 : :
876 [ - + ]: 246742 : Assert(!BTreeTupleIsPivot(base));
877 [ + - - + ]: 246742 : Assert(nhtids > 0 && nhtids <= PG_UINT16_MAX);
878 [ - + ]: 246742 : Assert(keysize == MAXALIGN(keysize));
879 : :
880 : : /* Determine final size of new tuple */
881 [ + + ]: 246742 : if (nhtids > 1)
882 : 221219 : newsize = MAXALIGN(keysize +
883 : : nhtids * sizeof(ItemPointerData));
884 : : else
885 : 25523 : newsize = keysize;
886 : :
887 [ - + ]: 246742 : Assert(newsize <= INDEX_SIZE_MASK);
888 [ - + ]: 246742 : Assert(newsize == MAXALIGN(newsize));
889 : :
890 : : /* Allocate memory using palloc0() (matches index_form_tuple()) */
891 : 246742 : itup = palloc0(newsize);
892 : 246742 : memcpy(itup, base, keysize);
893 : 246742 : itup->t_info &= ~INDEX_SIZE_MASK;
894 : 246742 : itup->t_info |= newsize;
895 [ + + ]: 246742 : if (nhtids > 1)
896 : : {
897 : : /* Form posting list tuple */
898 : 221219 : BTreeTupleSetPosting(itup, nhtids, keysize);
899 : 221219 : memcpy(BTreeTupleGetPosting(itup), htids,
900 : : sizeof(ItemPointerData) * nhtids);
901 [ - + ]: 221219 : Assert(_bt_posting_valid(itup));
902 : : }
903 : : else
904 : : {
905 : : /* Form standard non-pivot tuple */
906 : 25523 : itup->t_info &= ~INDEX_ALT_TID_MASK;
907 : 25523 : ItemPointerCopy(htids, &itup->t_tid);
908 [ - + ]: 25523 : Assert(ItemPointerIsValid(&itup->t_tid));
909 : : }
910 : :
911 : 246742 : return itup;
912 : : }
913 : :
914 : : /*
915 : : * Generate a replacement tuple by "updating" a posting list tuple so that it
916 : : * no longer has TIDs that need to be deleted.
917 : : *
918 : : * Used by both VACUUM and index deletion. Caller's vacposting argument
919 : : * points to the existing posting list tuple to be updated.
920 : : *
921 : : * On return, caller's vacposting argument will point to final "updated"
922 : : * tuple, which will be palloc()'d in caller's memory context.
923 : : */
924 : : void
925 : 36842 : _bt_update_posting(BTVacuumPosting vacposting)
926 : : {
927 : 36842 : IndexTuple origtuple = vacposting->itup;
928 : : uint32 keysize,
929 : : newsize;
930 : : IndexTuple itup;
931 : : int nhtids;
932 : : int ui,
933 : : d;
934 : : ItemPointer htids;
935 : :
936 : 36842 : nhtids = BTreeTupleGetNPosting(origtuple) - vacposting->ndeletedtids;
937 : :
938 [ - + ]: 36842 : Assert(_bt_posting_valid(origtuple));
939 [ + - - + ]: 36842 : Assert(nhtids > 0 && nhtids < BTreeTupleGetNPosting(origtuple));
940 : :
941 : : /*
942 : : * Determine final size of new tuple.
943 : : *
944 : : * This calculation needs to match the code used within _bt_form_posting()
945 : : * for new posting list tuples. We avoid calling _bt_form_posting() here
946 : : * to save ourselves a second memory allocation for a htids workspace.
947 : : */
2015 948 : 36842 : keysize = BTreeTupleGetPostingOffset(origtuple);
2019 949 [ + + ]: 36842 : if (nhtids > 1)
950 : 7726 : newsize = MAXALIGN(keysize +
951 : : nhtids * sizeof(ItemPointerData));
952 : : else
953 : 29116 : newsize = keysize;
954 : :
2014 955 [ - + ]: 36842 : Assert(newsize <= INDEX_SIZE_MASK);
956 [ - + ]: 36842 : Assert(newsize == MAXALIGN(newsize));
957 : :
958 : : /* Allocate memory using palloc0() (matches index_form_tuple()) */
2019 959 : 36842 : itup = palloc0(newsize);
960 : 36842 : memcpy(itup, origtuple, keysize);
961 : 36842 : itup->t_info &= ~INDEX_SIZE_MASK;
962 : 36842 : itup->t_info |= newsize;
963 : :
964 [ + + ]: 36842 : if (nhtids > 1)
965 : : {
966 : : /* Form posting list tuple */
967 : 7726 : BTreeTupleSetPosting(itup, nhtids, keysize);
968 : 7726 : htids = BTreeTupleGetPosting(itup);
969 : : }
970 : : else
971 : : {
972 : : /* Form standard non-pivot tuple */
973 : 29116 : itup->t_info &= ~INDEX_ALT_TID_MASK;
974 : 29116 : htids = &itup->t_tid;
975 : : }
976 : :
977 : 36842 : ui = 0;
978 : 36842 : d = 0;
979 [ + + ]: 200482 : for (int i = 0; i < BTreeTupleGetNPosting(origtuple); i++)
980 : : {
981 [ + + + + ]: 163640 : if (d < vacposting->ndeletedtids && vacposting->deletetids[d] == i)
982 : : {
983 : 79438 : d++;
984 : 79438 : continue;
985 : : }
986 : 84202 : htids[ui++] = *BTreeTupleGetPostingN(origtuple, i);
987 : : }
988 [ - + ]: 36842 : Assert(ui == nhtids);
989 [ - + ]: 36842 : Assert(d == vacposting->ndeletedtids);
990 [ + + - + ]: 36842 : Assert(nhtids == 1 || _bt_posting_valid(itup));
2014 991 [ + + - + ]: 36842 : Assert(nhtids > 1 || ItemPointerIsValid(&itup->t_tid));
992 : :
993 : : /* vacposting arg's itup will now point to updated version */
2019 994 : 36842 : vacposting->itup = itup;
995 : 36842 : }
996 : :
997 : : /*
998 : : * Prepare for a posting list split by swapping heap TID in newitem with heap
999 : : * TID from original posting list (the 'oposting' heap TID located at offset
1000 : : * 'postingoff'). Modifies newitem, so caller should pass their own private
1001 : : * copy that can safely be modified.
1002 : : *
1003 : : * Returns new posting list tuple, which is palloc()'d in caller's context.
1004 : : * This is guaranteed to be the same size as 'oposting'. Modified newitem is
1005 : : * what caller actually inserts. (This happens inside the same critical
1006 : : * section that performs an in-place update of old posting list using new
1007 : : * posting list returned here.)
1008 : : *
1009 : : * While the keys from newitem and oposting must be opclass equal, and must
1010 : : * generate identical output when run through the underlying type's output
1011 : : * function, it doesn't follow that their representations match exactly.
1012 : : * Caller must avoid assuming that there can't be representational differences
1013 : : * that make datums from oposting bigger or smaller than the corresponding
1014 : : * datums from newitem. For example, differences in TOAST input state might
1015 : : * break a faulty assumption about tuple size (the executor is entitled to
1016 : : * apply TOAST compression based on its own criteria). It also seems possible
1017 : : * that further representational variation will be introduced in the future,
1018 : : * in order to support nbtree features like page-level prefix compression.
1019 : : *
1020 : : * See nbtree/README for details on the design of posting list splits.
1021 : : */
1022 : : IndexTuple
1023 : 17222 : _bt_swap_posting(IndexTuple newitem, IndexTuple oposting, int postingoff)
1024 : : {
1025 : : int nhtids;
1026 : : char *replacepos;
1027 : : char *replaceposright;
1028 : : Size nmovebytes;
1029 : : IndexTuple nposting;
1030 : :
1031 : 17222 : nhtids = BTreeTupleGetNPosting(oposting);
1032 [ - + ]: 17222 : Assert(_bt_posting_valid(oposting));
1033 : :
1034 : : /*
1035 : : * The postingoff argument originated as a _bt_binsrch_posting() return
1036 : : * value. It will be 0 in the event of corruption that makes a leaf page
1037 : : * contain a non-pivot tuple that's somehow identical to newitem (no two
1038 : : * non-pivot tuples should ever have the same TID). This has been known
1039 : : * to happen in the field from time to time.
1040 : : *
1041 : : * Perform a basic sanity check to catch this case now.
1042 : : */
1576 1043 [ + - - + ]: 17222 : if (!(postingoff > 0 && postingoff < nhtids))
1576 pg@bowt.ie 1044 [ # # ]:UBC 0 : elog(ERROR, "posting list tuple with %d items cannot be split at offset %d",
1045 : : nhtids, postingoff);
1046 : :
1047 : : /*
1048 : : * Move item pointers in posting list to make a gap for the new item's
1049 : : * heap TID. We shift TIDs one place to the right, losing original
1050 : : * rightmost TID. (nmovebytes must not include TIDs to the left of
1051 : : * postingoff, nor the existing rightmost/max TID that gets overwritten.)
1052 : : */
2019 pg@bowt.ie 1053 :CBC 17222 : nposting = CopyIndexTuple(oposting);
1054 : 17222 : replacepos = (char *) BTreeTupleGetPostingN(nposting, postingoff);
1055 : 17222 : replaceposright = (char *) BTreeTupleGetPostingN(nposting, postingoff + 1);
1056 : 17222 : nmovebytes = (nhtids - postingoff - 1) * sizeof(ItemPointerData);
1057 : 17222 : memmove(replaceposright, replacepos, nmovebytes);
1058 : :
1059 : : /* Fill the gap at postingoff with TID of new item (original new TID) */
1060 [ + - - + ]: 17222 : Assert(!BTreeTupleIsPivot(newitem) && !BTreeTupleIsPosting(newitem));
1061 : 17222 : ItemPointerCopy(&newitem->t_tid, (ItemPointer) replacepos);
1062 : :
1063 : : /* Now copy oposting's rightmost/max TID into new item (final new TID) */
1064 : 17222 : ItemPointerCopy(BTreeTupleGetMaxHeapTID(oposting), &newitem->t_tid);
1065 : :
1066 [ - + ]: 17222 : Assert(ItemPointerCompare(BTreeTupleGetMaxHeapTID(nposting),
1067 : : BTreeTupleGetHeapTID(newitem)) < 0);
1068 [ - + ]: 17222 : Assert(_bt_posting_valid(nposting));
1069 : :
1070 : 17222 : return nposting;
1071 : : }
1072 : :
1073 : : /*
1074 : : * Verify posting list invariants for "posting", which must be a posting list
1075 : : * tuple. Used within assertions.
1076 : : */
1077 : : #ifdef USE_ASSERT_CHECKING
1078 : : static bool
1079 : 406487 : _bt_posting_valid(IndexTuple posting)
1080 : : {
1081 : : ItemPointerData last;
1082 : : ItemPointer htid;
1083 : :
1084 [ + - - + ]: 406487 : if (!BTreeTupleIsPosting(posting) || BTreeTupleGetNPosting(posting) < 2)
2019 pg@bowt.ie 1085 :UBC 0 : return false;
1086 : :
1087 : : /* Remember first heap TID for loop */
2019 pg@bowt.ie 1088 :CBC 406487 : ItemPointerCopy(BTreeTupleGetHeapTID(posting), &last);
1089 [ - + ]: 406487 : if (!ItemPointerIsValid(&last))
2019 pg@bowt.ie 1090 :UBC 0 : return false;
1091 : :
1092 : : /* Iterate, starting from second TID */
2019 pg@bowt.ie 1093 [ + + ]:CBC 7893245 : for (int i = 1; i < BTreeTupleGetNPosting(posting); i++)
1094 : : {
1095 : 7486758 : htid = BTreeTupleGetPostingN(posting, i);
1096 : :
1097 [ - + ]: 7486758 : if (!ItemPointerIsValid(htid))
2019 pg@bowt.ie 1098 :UBC 0 : return false;
2019 pg@bowt.ie 1099 [ - + ]:CBC 7486758 : if (ItemPointerCompare(htid, &last) <= 0)
2019 pg@bowt.ie 1100 :UBC 0 : return false;
2019 pg@bowt.ie 1101 :CBC 7486758 : ItemPointerCopy(htid, &last);
1102 : : }
1103 : :
1104 : 406487 : return true;
1105 : : }
1106 : : #endif
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