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
924 pg@bowt.ie 59 :CBC 13389 : _bt_dedup_pass(Relation rel, Buffer buf, IndexTuple newitem, Size newitemsz,
60 : : bool bottomupdedup)
61 : : {
62 : : OffsetNumber offnum,
63 : : minoff,
64 : : maxoff;
2071 65 : 13389 : Page page = BufferGetPage(buf);
1306 michael@paquier.xyz 66 : 13389 : BTPageOpaque opaque = BTPageGetOpaque(page);
67 : : Page newpage;
68 : : BTDedupState state;
1301 tgl@sss.pgh.pa.us 69 : 13389 : Size pagesaving PG_USED_FOR_ASSERTS_ONLY = 0;
2071 pg@bowt.ie 70 : 13389 : bool singlevalstrat = false;
2040 71 : 13389 : int nkeyatts = IndexRelationGetNumberOfKeyAttributes(rel);
72 : :
73 : : /* Passed-in newitemsz is MAXALIGNED but does not include line pointer */
2071 74 : 13389 : 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 : 13389 : state = (BTDedupState) palloc(sizeof(BTDedupStateData));
86 : 13389 : state->deduplicate = true;
1957 87 : 13389 : state->nmaxitems = 0;
231 88 : 13389 : state->maxpostingsize = Min(BTMaxItemSize / 2, INDEX_SIZE_MASK);
89 : : /* Metadata about base tuple of current pending posting list */
2071 90 : 13389 : state->base = NULL;
91 : 13389 : state->baseoff = InvalidOffsetNumber;
92 : 13389 : state->basetupsize = 0;
93 : : /* Metadata about current pending posting list TIDs */
94 : 13389 : state->htids = palloc(state->maxpostingsize);
95 : 13389 : state->nhtids = 0;
96 : 13389 : state->nitems = 0;
97 : : /* Size of all physical tuples to be replaced by pending posting list */
98 : 13389 : state->phystupsize = 0;
99 : : /* nintervals should be initialized to zero */
100 : 13389 : state->nintervals = 0;
101 : :
1806 102 [ + + ]: 13389 : minoff = P_FIRSTDATAKEY(opaque);
103 : 13389 : 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 : : */
1498 109 [ + + ]: 13389 : if (!bottomupdedup)
2071 110 : 11672 : 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 : 13389 : newpage = PageGetTempPageCopySpecial(page);
120 : 13389 : PageSetLSN(newpage, PageGetLSN(page));
121 : :
122 : : /* Copy high key, if any */
123 [ + + ]: 13389 : if (!P_RIGHTMOST(opaque))
124 : : {
125 : 10559 : ItemId hitemid = PageGetItemId(page, P_HIKEY);
126 : 10559 : Size hitemsz = ItemIdGetLength(hitemid);
127 : 10559 : IndexTuple hitem = (IndexTuple) PageGetItem(page, hitemid);
128 : :
1 peter@eisentraut.org 129 [ - + ]:GNC 10559 : if (PageAddItem(newpage, hitem, hitemsz, P_HIKEY, false, false) == InvalidOffsetNumber)
2071 pg@bowt.ie 130 [ # # ]:UBC 0 : elog(ERROR, "deduplication failed to add highkey");
131 : : }
132 : :
2071 pg@bowt.ie 133 :CBC 13389 : for (offnum = minoff;
134 [ + + ]: 3013203 : offnum <= maxoff;
135 : 2999814 : offnum = OffsetNumberNext(offnum))
136 : : {
137 : 2999814 : ItemId itemid = PageGetItemId(page, offnum);
138 : 2999814 : IndexTuple itup = (IndexTuple) PageGetItem(page, itemid);
139 : :
140 [ - + ]: 2999814 : Assert(!ItemIdIsDead(itemid));
141 : :
142 [ + + ]: 2999814 : if (offnum == minoff)
143 : : {
144 : : /*
145 : : * No previous/base tuple for the data item -- use the data item
146 : : * as base tuple of pending posting list
147 : : */
148 : 13389 : _bt_dedup_start_pending(state, itup, offnum);
149 : : }
150 [ + + + + ]: 5971953 : else if (state->deduplicate &&
2040 151 [ + + ]: 3398967 : _bt_keep_natts_fast(rel, state->base, itup) > nkeyatts &&
2071 152 : 413439 : _bt_dedup_save_htid(state, itup))
153 : : {
154 : : /*
155 : : * Tuple is equal to base tuple of pending posting list. Heap
156 : : * TID(s) for itup have been saved in state.
157 : : */
158 : : }
159 : : else
160 : : {
161 : : /*
162 : : * Tuple is not equal to pending posting list tuple, or
163 : : * _bt_dedup_save_htid() opted to not merge current item into
164 : : * pending posting list for some other reason (e.g., adding more
165 : : * TIDs would have caused posting list to exceed current
166 : : * maxpostingsize).
167 : : *
168 : : * If state contains pending posting list with more than one item,
169 : : * form new posting tuple and add it to our temp page (newpage).
170 : : * Else add pending interval's base tuple to the temp page as-is.
171 : : */
172 : 2579336 : pagesaving += _bt_dedup_finish_pending(newpage, state);
173 : :
174 [ + + ]: 2579336 : if (singlevalstrat)
175 : : {
176 : : /*
177 : : * Single value strategy's extra steps.
178 : : *
179 : : * Lower maxpostingsize for sixth and final large posting list
180 : : * tuple at the point where 5 maxpostingsize-capped tuples
181 : : * have either been formed or observed.
182 : : *
183 : : * When a sixth maxpostingsize-capped item is formed/observed,
184 : : * stop merging together tuples altogether. The few tuples
185 : : * that remain at the end of the page won't be merged together
186 : : * at all (at least not until after a future page split takes
187 : : * place, when this page's newly allocated right sibling page
188 : : * gets its first deduplication pass).
189 : : */
1957 190 [ + + ]: 2431 : if (state->nmaxitems == 5)
2071 191 : 304 : _bt_singleval_fillfactor(page, state, newitemsz);
1957 192 [ + + ]: 2127 : else if (state->nmaxitems == 6)
193 : : {
2071 194 : 106 : state->deduplicate = false;
195 : 106 : singlevalstrat = false; /* won't be back here */
196 : : }
197 : : }
198 : :
199 : : /* itup starts new pending posting list */
200 : 2579336 : _bt_dedup_start_pending(state, itup, offnum);
201 : : }
202 : : }
203 : :
204 : : /* Handle the last item */
205 : 13389 : pagesaving += _bt_dedup_finish_pending(newpage, state);
206 : :
207 : : /*
208 : : * If no items suitable for deduplication were found, newpage must be
209 : : * exactly the same as the original page, so just return from function.
210 : : *
211 : : * We could determine whether or not to proceed on the basis the space
212 : : * savings being sufficient to avoid an immediate page split instead. We
213 : : * don't do that because there is some small value in nbtsplitloc.c always
214 : : * operating against a page that is fully deduplicated (apart from
215 : : * newitem). Besides, most of the cost has already been paid.
216 : : */
217 [ + + ]: 13389 : if (state->nintervals == 0)
218 : : {
219 : : /* cannot leak memory here */
220 : 2338 : pfree(newpage);
221 : 2338 : pfree(state->htids);
222 : 2338 : pfree(state);
223 : 2338 : return;
224 : : }
225 : :
226 : : /*
227 : : * By here, it's clear that deduplication will definitely go ahead.
228 : : *
229 : : * Clear the BTP_HAS_GARBAGE page flag. The index must be a heapkeyspace
230 : : * index, and as such we'll never pay attention to BTP_HAS_GARBAGE anyway.
231 : : * But keep things tidy.
232 : : */
233 [ - + ]: 11051 : if (P_HAS_GARBAGE(opaque))
234 : : {
1306 michael@paquier.xyz 235 :UBC 0 : BTPageOpaque nopaque = BTPageGetOpaque(newpage);
236 : :
2071 pg@bowt.ie 237 : 0 : nopaque->btpo_flags &= ~BTP_HAS_GARBAGE;
238 : : }
239 : :
2071 pg@bowt.ie 240 :CBC 11051 : START_CRIT_SECTION();
241 : :
242 : 11051 : PageRestoreTempPage(newpage, page);
243 : 11051 : MarkBufferDirty(buf);
244 : :
245 : : /* XLOG stuff */
246 [ + + + + : 11051 : if (RelationNeedsWAL(rel))
+ - + - ]
247 : : {
248 : : XLogRecPtr recptr;
249 : : xl_btree_dedup xlrec_dedup;
250 : :
251 : 10988 : xlrec_dedup.nintervals = state->nintervals;
252 : :
253 : 10988 : XLogBeginInsert();
254 : 10988 : XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
259 peter@eisentraut.org 255 : 10988 : XLogRegisterData(&xlrec_dedup, SizeOfBtreeDedup);
256 : :
257 : : /*
258 : : * The intervals array is not in the buffer, but pretend that it is.
259 : : * When XLogInsert stores the whole buffer, the array need not be
260 : : * stored too.
261 : : */
262 : 10988 : XLogRegisterBufData(0, state->intervals,
2071 pg@bowt.ie 263 : 10988 : state->nintervals * sizeof(BTDedupInterval));
264 : :
265 : 10988 : recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_DEDUP);
266 : :
267 : 10988 : PageSetLSN(page, recptr);
268 : : }
269 : :
270 [ - + ]: 11051 : END_CRIT_SECTION();
271 : :
272 : : /* Local space accounting should agree with page accounting */
273 [ + + - + ]: 11051 : Assert(pagesaving < newitemsz || PageGetExactFreeSpace(page) >= newitemsz);
274 : :
275 : : /* cannot leak memory here */
276 : 11051 : pfree(state->htids);
277 : 11051 : pfree(state);
278 : : }
279 : :
280 : : /*
281 : : * Perform bottom-up index deletion pass.
282 : : *
283 : : * See if duplicate index tuples (plus certain nearby tuples) are eligible to
284 : : * be deleted via bottom-up index deletion. The high level goal here is to
285 : : * entirely prevent "unnecessary" page splits caused by MVCC version churn
286 : : * from UPDATEs (when the UPDATEs don't logically modify any of the columns
287 : : * covered by the 'rel' index). This is qualitative, not quantitative -- we
288 : : * do not particularly care about once-off opportunities to delete many index
289 : : * tuples together.
290 : : *
291 : : * See nbtree/README for details on the design of nbtree bottom-up deletion.
292 : : * See access/tableam.h for a description of how we're expected to cooperate
293 : : * with the tableam.
294 : : *
295 : : * Returns true on success, in which case caller can assume page split will be
296 : : * avoided for a reasonable amount of time. Returns false when caller should
297 : : * deduplicate the page (if possible at all).
298 : : *
299 : : * Note: Occasionally we return true despite failing to delete enough items to
300 : : * avoid a split. This makes caller skip deduplication and go split the page
301 : : * right away. Our return value is always just advisory information.
302 : : *
303 : : * Note: Caller should have already deleted all existing items with their
304 : : * LP_DEAD bits set.
305 : : */
306 : : bool
1749 307 : 1920 : _bt_bottomupdel_pass(Relation rel, Buffer buf, Relation heapRel,
308 : : Size newitemsz)
309 : : {
310 : : OffsetNumber offnum,
311 : : minoff,
312 : : maxoff;
313 : 1920 : Page page = BufferGetPage(buf);
1306 michael@paquier.xyz 314 : 1920 : BTPageOpaque opaque = BTPageGetOpaque(page);
315 : : BTDedupState state;
316 : : TM_IndexDeleteOp delstate;
317 : : bool neverdedup;
1749 pg@bowt.ie 318 : 1920 : int nkeyatts = IndexRelationGetNumberOfKeyAttributes(rel);
319 : :
320 : : /* Passed-in newitemsz is MAXALIGNED but does not include line pointer */
321 : 1920 : newitemsz += sizeof(ItemIdData);
322 : :
323 : : /* Initialize deduplication state */
324 : 1920 : state = (BTDedupState) palloc(sizeof(BTDedupStateData));
325 : 1920 : state->deduplicate = true;
326 : 1920 : state->nmaxitems = 0;
327 : 1920 : state->maxpostingsize = BLCKSZ; /* We're not really deduplicating */
328 : 1920 : state->base = NULL;
329 : 1920 : state->baseoff = InvalidOffsetNumber;
330 : 1920 : state->basetupsize = 0;
331 : 1920 : state->htids = palloc(state->maxpostingsize);
332 : 1920 : state->nhtids = 0;
333 : 1920 : state->nitems = 0;
334 : 1920 : state->phystupsize = 0;
335 : 1920 : state->nintervals = 0;
336 : :
337 : : /*
338 : : * Initialize tableam state that describes bottom-up index deletion
339 : : * operation.
340 : : *
341 : : * We'll go on to ask the tableam to search for TIDs whose index tuples we
342 : : * can safely delete. The tableam will search until our leaf page space
343 : : * target is satisfied, or until the cost of continuing with the tableam
344 : : * operation seems too high. It focuses its efforts on TIDs associated
345 : : * with duplicate index tuples that we mark "promising".
346 : : *
347 : : * This space target is a little arbitrary. The tableam must be able to
348 : : * keep the costs and benefits in balance. We provide the tableam with
349 : : * exhaustive information about what might work, without directly
350 : : * concerning ourselves with avoiding work during the tableam call. Our
351 : : * role in costing the bottom-up deletion process is strictly advisory.
352 : : */
1454 353 : 1920 : delstate.irel = rel;
354 : 1920 : delstate.iblknum = BufferGetBlockNumber(buf);
1749 355 : 1920 : delstate.bottomup = true;
356 : 1920 : delstate.bottomupfreespace = Max(BLCKSZ / 16, newitemsz);
357 : 1920 : delstate.ndeltids = 0;
358 : 1920 : delstate.deltids = palloc(MaxTIDsPerBTreePage * sizeof(TM_IndexDelete));
359 : 1920 : delstate.status = palloc(MaxTIDsPerBTreePage * sizeof(TM_IndexStatus));
360 : :
361 [ + + ]: 1920 : minoff = P_FIRSTDATAKEY(opaque);
362 : 1920 : maxoff = PageGetMaxOffsetNumber(page);
363 : 1920 : for (offnum = minoff;
364 [ + + ]: 540332 : offnum <= maxoff;
365 : 538412 : offnum = OffsetNumberNext(offnum))
366 : : {
367 : 538412 : ItemId itemid = PageGetItemId(page, offnum);
368 : 538412 : IndexTuple itup = (IndexTuple) PageGetItem(page, itemid);
369 : :
370 [ - + ]: 538412 : Assert(!ItemIdIsDead(itemid));
371 : :
372 [ + + ]: 538412 : if (offnum == minoff)
373 : : {
374 : : /* itup starts first pending interval */
375 : 1920 : _bt_dedup_start_pending(state, itup, offnum);
376 : : }
377 [ + + + - ]: 609865 : else if (_bt_keep_natts_fast(rel, state->base, itup) > nkeyatts &&
378 : 73373 : _bt_dedup_save_htid(state, itup))
379 : : {
380 : : /* Tuple is equal; just added its TIDs to pending interval */
381 : : }
382 : : else
383 : : {
384 : : /* Finalize interval -- move its TIDs to delete state */
385 : 463119 : _bt_bottomupdel_finish_pending(page, state, &delstate);
386 : :
387 : : /* itup starts new pending interval */
388 : 463119 : _bt_dedup_start_pending(state, itup, offnum);
389 : : }
390 : : }
391 : : /* Finalize final interval -- move its TIDs to delete state */
392 : 1920 : _bt_bottomupdel_finish_pending(page, state, &delstate);
393 : :
394 : : /*
395 : : * We don't give up now in the event of having few (or even zero)
396 : : * promising tuples for the tableam because it's not up to us as the index
397 : : * AM to manage costs (note that the tableam might have heuristics of its
398 : : * own that work out what to do). We should at least avoid having our
399 : : * caller do a useless deduplication pass after we return in the event of
400 : : * zero promising tuples, though.
401 : : */
402 : 1920 : neverdedup = false;
403 [ + + ]: 1920 : if (state->nintervals == 0)
404 : 5 : neverdedup = true;
405 : :
406 : 1920 : pfree(state->htids);
407 : 1920 : pfree(state);
408 : :
409 : : /* Ask tableam which TIDs are deletable, then physically delete them */
410 : 1920 : _bt_delitems_delete_check(rel, buf, heapRel, &delstate);
411 : :
412 : 1920 : pfree(delstate.deltids);
413 : 1920 : pfree(delstate.status);
414 : :
415 : : /* Report "success" to caller unconditionally to avoid deduplication */
416 [ + + ]: 1920 : if (neverdedup)
417 : 5 : return true;
418 : :
419 : : /* Don't dedup when we won't end up back here any time soon anyway */
420 : 1915 : return PageGetExactFreeSpace(page) >= Max(BLCKSZ / 24, newitemsz);
421 : : }
422 : :
423 : : /*
424 : : * Create a new pending posting list tuple based on caller's base tuple.
425 : : *
426 : : * Every tuple processed by deduplication either becomes the base tuple for a
427 : : * posting list, or gets its heap TID(s) accepted into a pending posting list.
428 : : * A tuple that starts out as the base tuple for a posting list will only
429 : : * actually be rewritten within _bt_dedup_finish_pending() when it turns out
430 : : * that there are duplicates that can be merged into the base tuple.
431 : : */
432 : : void
2071 433 : 5843739 : _bt_dedup_start_pending(BTDedupState state, IndexTuple base,
434 : : OffsetNumber baseoff)
435 : : {
436 [ - + ]: 5843739 : Assert(state->nhtids == 0);
437 [ - + ]: 5843739 : Assert(state->nitems == 0);
438 [ - + ]: 5843739 : Assert(!BTreeTupleIsPivot(base));
439 : :
440 : : /*
441 : : * Copy heap TID(s) from new base tuple for new candidate posting list
442 : : * into working state's array
443 : : */
444 [ + + ]: 5843739 : if (!BTreeTupleIsPosting(base))
445 : : {
446 : 4868117 : memcpy(state->htids, &base->t_tid, sizeof(ItemPointerData));
447 : 4868117 : state->nhtids = 1;
448 : 4868117 : state->basetupsize = IndexTupleSize(base);
449 : : }
450 : : else
451 : : {
452 : : int nposting;
453 : :
454 : 975622 : nposting = BTreeTupleGetNPosting(base);
455 : 975622 : memcpy(state->htids, BTreeTupleGetPosting(base),
456 : : sizeof(ItemPointerData) * nposting);
457 : 975622 : state->nhtids = nposting;
458 : : /* basetupsize should not include existing posting list */
459 : 975622 : state->basetupsize = BTreeTupleGetPostingOffset(base);
460 : : }
461 : :
462 : : /*
463 : : * Save new base tuple itself -- it'll be needed if we actually create a
464 : : * new posting list from new pending posting list.
465 : : *
466 : : * Must maintain physical size of all existing tuples (including line
467 : : * pointer overhead) so that we can calculate space savings on page.
468 : : */
469 : 5843739 : state->nitems = 1;
470 : 5843739 : state->base = base;
471 : 5843739 : state->baseoff = baseoff;
472 : 5843739 : state->phystupsize = MAXALIGN(IndexTupleSize(base)) + sizeof(ItemIdData);
473 : : /* Also save baseoff in pending state for interval */
474 : 5843739 : state->intervals[state->nintervals].baseoff = state->baseoff;
475 : 5843739 : }
476 : :
477 : : /*
478 : : * Save itup heap TID(s) into pending posting list where possible.
479 : : *
480 : : * Returns bool indicating if the pending posting list managed by state now
481 : : * includes itup's heap TID(s).
482 : : */
483 : : bool
484 : 1260141 : _bt_dedup_save_htid(BTDedupState state, IndexTuple itup)
485 : : {
486 : : int nhtids;
487 : : ItemPointer htids;
488 : : Size mergedtupsz;
489 : :
490 [ - + ]: 1260141 : Assert(!BTreeTupleIsPivot(itup));
491 : :
492 [ + + ]: 1260141 : if (!BTreeTupleIsPosting(itup))
493 : : {
494 : 1253906 : nhtids = 1;
495 : 1253906 : htids = &itup->t_tid;
496 : : }
497 : : else
498 : : {
499 : 6235 : nhtids = BTreeTupleGetNPosting(itup);
500 : 6235 : htids = BTreeTupleGetPosting(itup);
501 : : }
502 : :
503 : : /*
504 : : * Don't append (have caller finish pending posting list as-is) if
505 : : * appending heap TID(s) from itup would put us over maxpostingsize limit.
506 : : *
507 : : * This calculation needs to match the code used within _bt_form_posting()
508 : : * for new posting list tuples.
509 : : */
510 : 1260141 : mergedtupsz = MAXALIGN(state->basetupsize +
511 : : (state->nhtids + nhtids) * sizeof(ItemPointerData));
512 : :
513 [ + + ]: 1260141 : if (mergedtupsz > state->maxpostingsize)
514 : : {
515 : : /*
516 : : * Count this as an oversized item for single value strategy, though
517 : : * only when there are 50 TIDs in the final posting list tuple. This
518 : : * limit (which is fairly arbitrary) avoids confusion about how many
519 : : * 1/6 of a page tuples have been encountered/created by the current
520 : : * deduplication pass.
521 : : *
522 : : * Note: We deliberately don't consider which deduplication pass
523 : : * merged together tuples to create this item (could be a previous
524 : : * deduplication pass, or current pass). See _bt_do_singleval()
525 : : * comments.
526 : : */
1957 527 [ + + ]: 10320 : if (state->nhtids > 50)
528 : 9759 : state->nmaxitems++;
529 : :
2071 530 : 10320 : return false;
531 : : }
532 : :
533 : : /*
534 : : * Save heap TIDs to pending posting list tuple -- itup can be merged into
535 : : * pending posting list
536 : : */
537 : 1249821 : state->nitems++;
538 : 1249821 : memcpy(state->htids + state->nhtids, htids,
539 : : sizeof(ItemPointerData) * nhtids);
540 : 1249821 : state->nhtids += nhtids;
541 : 1249821 : state->phystupsize += MAXALIGN(IndexTupleSize(itup)) + sizeof(ItemIdData);
542 : :
543 : 1249821 : return true;
544 : : }
545 : :
546 : : /*
547 : : * Finalize pending posting list tuple, and add it to the page. Final tuple
548 : : * is based on saved base tuple, and saved list of heap TIDs.
549 : : *
550 : : * Returns space saving from deduplicating to make a new posting list tuple.
551 : : * Note that this includes line pointer overhead. This is zero in the case
552 : : * where no deduplication was possible.
553 : : */
554 : : Size
555 : 3019397 : _bt_dedup_finish_pending(Page newpage, BTDedupState state)
556 : : {
557 : : OffsetNumber tupoff;
558 : : Size tuplesz;
559 : : Size spacesaving;
560 : :
561 [ - + ]: 3019397 : Assert(state->nitems > 0);
562 [ - + ]: 3019397 : Assert(state->nitems <= state->nhtids);
563 [ - + ]: 3019397 : Assert(state->intervals[state->nintervals].baseoff == state->baseoff);
564 : :
565 : 3019397 : tupoff = OffsetNumberNext(PageGetMaxOffsetNumber(newpage));
566 [ + + ]: 3019397 : if (state->nitems == 1)
567 : : {
568 : : /* Use original, unchanged base tuple */
569 : 2818514 : tuplesz = IndexTupleSize(state->base);
1180 570 [ - + ]: 2818514 : Assert(tuplesz == MAXALIGN(IndexTupleSize(state->base)));
231 571 [ - + ]: 2818514 : Assert(tuplesz <= BTMaxItemSize);
1 peter@eisentraut.org 572 [ - + ]:GNC 2818514 : if (PageAddItem(newpage, state->base, tuplesz, tupoff, false, false) == InvalidOffsetNumber)
2071 pg@bowt.ie 573 [ # # ]:UBC 0 : elog(ERROR, "deduplication failed to add tuple to page");
574 : :
2071 pg@bowt.ie 575 :CBC 2818514 : spacesaving = 0;
576 : : }
577 : : else
578 : : {
579 : : IndexTuple final;
580 : :
581 : : /* Form a tuple with a posting list */
582 : 200883 : final = _bt_form_posting(state->base, state->htids, state->nhtids);
583 : 200883 : tuplesz = IndexTupleSize(final);
584 [ - + ]: 200883 : Assert(tuplesz <= state->maxpostingsize);
585 : :
586 : : /* Save final number of items for posting list */
587 : 200883 : state->intervals[state->nintervals].nitems = state->nitems;
588 : :
589 [ - + ]: 200883 : Assert(tuplesz == MAXALIGN(IndexTupleSize(final)));
231 590 [ - + ]: 200883 : Assert(tuplesz <= BTMaxItemSize);
1 peter@eisentraut.org 591 [ - + ]:GNC 200883 : if (PageAddItem(newpage, final, tuplesz, tupoff, false, false) == InvalidOffsetNumber)
2071 pg@bowt.ie 592 [ # # ]:UBC 0 : elog(ERROR, "deduplication failed to add tuple to page");
593 : :
2071 pg@bowt.ie 594 :CBC 200883 : pfree(final);
595 : 200883 : spacesaving = state->phystupsize - (tuplesz + sizeof(ItemIdData));
596 : : /* Increment nintervals, since we wrote a new posting list tuple */
597 : 200883 : state->nintervals++;
598 [ + - - + ]: 200883 : Assert(spacesaving > 0 && spacesaving < BLCKSZ);
599 : : }
600 : :
601 : : /* Reset state for next pending posting list */
602 : 3019397 : state->nhtids = 0;
603 : 3019397 : state->nitems = 0;
604 : 3019397 : state->phystupsize = 0;
605 : :
606 : 3019397 : return spacesaving;
607 : : }
608 : :
609 : : /*
610 : : * Finalize interval during bottom-up index deletion.
611 : : *
612 : : * During a bottom-up pass we expect that TIDs will be recorded in dedup state
613 : : * first, and then get moved over to delstate (in variable-sized batches) by
614 : : * calling here. Call here happens when the number of TIDs in a dedup
615 : : * interval is known, and interval gets finalized (i.e. when caller sees next
616 : : * tuple on the page is not a duplicate, or when caller runs out of tuples to
617 : : * process from leaf page).
618 : : *
619 : : * This is where bottom-up deletion determines and remembers which entries are
620 : : * duplicates. This will be important information to the tableam delete
621 : : * infrastructure later on. Plain index tuple duplicates are marked
622 : : * "promising" here, per tableam contract.
623 : : *
624 : : * Our approach to marking entries whose TIDs come from posting lists is more
625 : : * complicated. Posting lists can only be formed by a deduplication pass (or
626 : : * during an index build), so recent version churn affecting the pointed-to
627 : : * logical rows is not particularly likely. We may still give a weak signal
628 : : * about posting list tuples' entries (by marking just one of its TIDs/entries
629 : : * promising), though this is only a possibility in the event of further
630 : : * duplicate index tuples in final interval that covers posting list tuple (as
631 : : * in the plain tuple case). A weak signal/hint will be useful to the tableam
632 : : * when it has no stronger signal to go with for the deletion operation as a
633 : : * whole.
634 : : *
635 : : * The heuristics we use work well in practice because we only need to give
636 : : * the tableam the right _general_ idea about where to look. Garbage tends to
637 : : * naturally get concentrated in relatively few table blocks with workloads
638 : : * that bottom-up deletion targets. The tableam cannot possibly rank all
639 : : * available table blocks sensibly based on the hints we provide, but that's
640 : : * okay -- only the extremes matter. The tableam just needs to be able to
641 : : * predict which few table blocks will have the most tuples that are safe to
642 : : * delete for each deletion operation, with low variance across related
643 : : * deletion operations.
644 : : */
645 : : static void
1749 646 : 465039 : _bt_bottomupdel_finish_pending(Page page, BTDedupState state,
647 : : TM_IndexDeleteOp *delstate)
648 : : {
649 : 465039 : bool dupinterval = (state->nitems > 1);
650 : :
651 [ - + ]: 465039 : Assert(state->nitems > 0);
652 [ - + ]: 465039 : Assert(state->nitems <= state->nhtids);
653 [ - + ]: 465039 : Assert(state->intervals[state->nintervals].baseoff == state->baseoff);
654 : :
655 [ + + ]: 1003451 : for (int i = 0; i < state->nitems; i++)
656 : : {
657 : 538412 : OffsetNumber offnum = state->baseoff + i;
658 : 538412 : ItemId itemid = PageGetItemId(page, offnum);
659 : 538412 : IndexTuple itup = (IndexTuple) PageGetItem(page, itemid);
660 : 538412 : TM_IndexDelete *ideltid = &delstate->deltids[delstate->ndeltids];
661 : 538412 : TM_IndexStatus *istatus = &delstate->status[delstate->ndeltids];
662 : :
663 [ + + ]: 538412 : if (!BTreeTupleIsPosting(itup))
664 : : {
665 : : /* Simple case: A plain non-pivot tuple */
666 : 428694 : ideltid->tid = itup->t_tid;
667 : 428694 : ideltid->id = delstate->ndeltids;
668 : 428694 : istatus->idxoffnum = offnum;
669 : 428694 : istatus->knowndeletable = false; /* for now */
670 : 428694 : istatus->promising = dupinterval; /* simple rule */
671 : 428694 : istatus->freespace = ItemIdGetLength(itemid) + sizeof(ItemIdData);
672 : :
673 : 428694 : delstate->ndeltids++;
674 : : }
675 : : else
676 : : {
677 : : /*
678 : : * Complicated case: A posting list tuple.
679 : : *
680 : : * We make the conservative assumption that there can only be at
681 : : * most one affected logical row per posting list tuple. There
682 : : * will be at most one promising entry in deltids to represent
683 : : * this presumed lone logical row. Note that this isn't even
684 : : * considered unless the posting list tuple is also in an interval
685 : : * of duplicates -- this complicated rule is just a variant of the
686 : : * simple rule used to decide if plain index tuples are promising.
687 : : */
688 : 109718 : int nitem = BTreeTupleGetNPosting(itup);
689 : 109718 : bool firstpromising = false;
690 : 109718 : bool lastpromising = false;
691 : :
692 [ - + ]: 109718 : Assert(_bt_posting_valid(itup));
693 : :
694 [ + + ]: 109718 : if (dupinterval)
695 : : {
696 : : /*
697 : : * Complicated rule: either the first or last TID in the
698 : : * posting list gets marked promising (if any at all)
699 : : */
700 : : BlockNumber minblocklist,
701 : : midblocklist,
702 : : maxblocklist;
703 : : ItemPointer mintid,
704 : : midtid,
705 : : maxtid;
706 : :
707 : 10096 : mintid = BTreeTupleGetHeapTID(itup);
708 : 10096 : midtid = BTreeTupleGetPostingN(itup, nitem / 2);
709 : 10096 : maxtid = BTreeTupleGetMaxHeapTID(itup);
710 : 10096 : minblocklist = ItemPointerGetBlockNumber(mintid);
711 : 10096 : midblocklist = ItemPointerGetBlockNumber(midtid);
712 : 10096 : maxblocklist = ItemPointerGetBlockNumber(maxtid);
713 : :
714 : : /* Only entry with predominant table block can be promising */
715 : 10096 : firstpromising = (minblocklist == midblocklist);
716 [ + + + + ]: 10096 : lastpromising = (!firstpromising &&
717 : : midblocklist == maxblocklist);
718 : : }
719 : :
720 [ + + ]: 606688 : for (int p = 0; p < nitem; p++)
721 : : {
722 : 496970 : ItemPointer htid = BTreeTupleGetPostingN(itup, p);
723 : :
724 : 496970 : ideltid->tid = *htid;
725 : 496970 : ideltid->id = delstate->ndeltids;
726 : 496970 : istatus->idxoffnum = offnum;
727 : 496970 : istatus->knowndeletable = false; /* for now */
728 : 496970 : istatus->promising = false;
729 [ + + + + : 496970 : if ((firstpromising && p == 0) ||
+ + ]
730 [ + + ]: 64119 : (lastpromising && p == nitem - 1))
731 : 6924 : istatus->promising = true;
732 : 496970 : istatus->freespace = sizeof(ItemPointerData); /* at worst */
733 : :
734 : 496970 : ideltid++;
735 : 496970 : istatus++;
736 : 496970 : delstate->ndeltids++;
737 : : }
738 : : }
739 : : }
740 : :
741 [ + + ]: 465039 : if (dupinterval)
742 : : {
743 : 48753 : state->intervals[state->nintervals].nitems = state->nitems;
744 : 48753 : state->nintervals++;
745 : : }
746 : :
747 : : /* Reset state for next interval */
748 : 465039 : state->nhtids = 0;
749 : 465039 : state->nitems = 0;
750 : 465039 : state->phystupsize = 0;
751 : 465039 : }
752 : :
753 : : /*
754 : : * Determine if page non-pivot tuples (data items) are all duplicates of the
755 : : * same value -- if they are, deduplication's "single value" strategy should
756 : : * be applied. The general goal of this strategy is to ensure that
757 : : * nbtsplitloc.c (which uses its own single value strategy) will find a useful
758 : : * split point as further duplicates are inserted, and successive rightmost
759 : : * page splits occur among pages that store the same duplicate value. When
760 : : * the page finally splits, it should end up BTREE_SINGLEVAL_FILLFACTOR% full,
761 : : * just like it would if deduplication were disabled.
762 : : *
763 : : * We expect that affected workloads will require _several_ single value
764 : : * strategy deduplication passes (over a page that only stores duplicates)
765 : : * before the page is finally split. The first deduplication pass should only
766 : : * find regular non-pivot tuples. Later deduplication passes will find
767 : : * existing maxpostingsize-capped posting list tuples, which must be skipped
768 : : * over. The penultimate pass is generally the first pass that actually
769 : : * reaches _bt_singleval_fillfactor(), and so will deliberately leave behind a
770 : : * few untouched non-pivot tuples. The final deduplication pass won't free
771 : : * any space -- it will skip over everything without merging anything (it
772 : : * retraces the steps of the penultimate pass).
773 : : *
774 : : * Fortunately, having several passes isn't too expensive. Each pass (after
775 : : * the first pass) won't spend many cycles on the large posting list tuples
776 : : * left by previous passes. Each pass will find a large contiguous group of
777 : : * smaller duplicate tuples to merge together at the end of the page.
778 : : */
779 : : static bool
2071 780 : 11672 : _bt_do_singleval(Relation rel, Page page, BTDedupState state,
781 : : OffsetNumber minoff, IndexTuple newitem)
782 : : {
2040 783 : 11672 : int nkeyatts = IndexRelationGetNumberOfKeyAttributes(rel);
784 : : ItemId itemid;
785 : : IndexTuple itup;
786 : :
2071 787 : 11672 : itemid = PageGetItemId(page, minoff);
788 : 11672 : itup = (IndexTuple) PageGetItem(page, itemid);
789 : :
2040 790 [ + + ]: 11672 : if (_bt_keep_natts_fast(rel, newitem, itup) > nkeyatts)
791 : : {
2071 792 : 978 : itemid = PageGetItemId(page, PageGetMaxOffsetNumber(page));
793 : 978 : itup = (IndexTuple) PageGetItem(page, itemid);
794 : :
2040 795 [ + + ]: 978 : if (_bt_keep_natts_fast(rel, newitem, itup) > nkeyatts)
2071 796 : 626 : return true;
797 : : }
798 : :
799 : 11046 : return false;
800 : : }
801 : :
802 : : /*
803 : : * Lower maxpostingsize when using "single value" strategy, to avoid a sixth
804 : : * and final maxpostingsize-capped tuple. The sixth and final posting list
805 : : * tuple will end up somewhat smaller than the first five. (Note: The first
806 : : * five tuples could actually just be very large duplicate tuples that
807 : : * couldn't be merged together at all. Deduplication will simply not modify
808 : : * the page when that happens.)
809 : : *
810 : : * When there are six posting lists on the page (after current deduplication
811 : : * pass goes on to create/observe a sixth very large tuple), caller should end
812 : : * its deduplication pass. It isn't useful to try to deduplicate items that
813 : : * are supposed to end up on the new right sibling page following the
814 : : * anticipated page split. A future deduplication pass of future right
815 : : * sibling page might take care of it. (This is why the first single value
816 : : * strategy deduplication pass for a given leaf page will generally find only
817 : : * plain non-pivot tuples -- see _bt_do_singleval() comments.)
818 : : */
819 : : static void
820 : 304 : _bt_singleval_fillfactor(Page page, BTDedupState state, Size newitemsz)
821 : : {
822 : : Size leftfree;
823 : : int reduction;
824 : :
825 : : /* This calculation needs to match nbtsplitloc.c */
826 : 304 : leftfree = PageGetPageSize(page) - SizeOfPageHeaderData -
827 : : MAXALIGN(sizeof(BTPageOpaqueData));
828 : : /* Subtract size of new high key (includes pivot heap TID space) */
829 : 304 : leftfree -= newitemsz + MAXALIGN(sizeof(ItemPointerData));
830 : :
831 : : /*
832 : : * Reduce maxpostingsize by an amount equal to target free space on left
833 : : * half of page
834 : : */
835 : 304 : reduction = leftfree * ((100 - BTREE_SINGLEVAL_FILLFACTOR) / 100.0);
836 [ + - ]: 304 : if (state->maxpostingsize > reduction)
837 : 304 : state->maxpostingsize -= reduction;
838 : : else
2071 pg@bowt.ie 839 :UBC 0 : state->maxpostingsize = 0;
2071 pg@bowt.ie 840 :CBC 304 : }
841 : :
842 : : /*
843 : : * Build a posting list tuple based on caller's "base" index tuple and list of
844 : : * heap TIDs. When nhtids == 1, builds a standard non-pivot tuple without a
845 : : * posting list. (Posting list tuples can never have a single heap TID, partly
846 : : * because that ensures that deduplication always reduces final MAXALIGN()'d
847 : : * size of entire tuple.)
848 : : *
849 : : * Convention is that posting list starts at a MAXALIGN()'d offset (rather
850 : : * than a SHORTALIGN()'d offset), in line with the approach taken when
851 : : * appending a heap TID to new pivot tuple/high key during suffix truncation.
852 : : * This sometimes wastes a little space that was only needed as alignment
853 : : * padding in the original tuple. Following this convention simplifies the
854 : : * space accounting used when deduplicating a page (the same convention
855 : : * simplifies the accounting for choosing a point to split a page at).
856 : : *
857 : : * Note: Caller's "htids" array must be unique and already in ascending TID
858 : : * order. Any existing heap TIDs from "base" won't automatically appear in
859 : : * returned posting list tuple (they must be included in htids array.)
860 : : */
861 : : IndexTuple
862 : 253562 : _bt_form_posting(IndexTuple base, ItemPointer htids, int nhtids)
863 : : {
864 : : uint32 keysize,
865 : : newsize;
866 : : IndexTuple itup;
867 : :
868 [ + + ]: 253562 : if (BTreeTupleIsPosting(base))
869 : 73972 : keysize = BTreeTupleGetPostingOffset(base);
870 : : else
871 : 179590 : keysize = IndexTupleSize(base);
872 : :
873 [ - + ]: 253562 : Assert(!BTreeTupleIsPivot(base));
874 [ + - - + ]: 253562 : Assert(nhtids > 0 && nhtids <= PG_UINT16_MAX);
875 [ - + ]: 253562 : Assert(keysize == MAXALIGN(keysize));
876 : :
877 : : /* Determine final size of new tuple */
878 [ + + ]: 253562 : if (nhtids > 1)
879 : 220981 : newsize = MAXALIGN(keysize +
880 : : nhtids * sizeof(ItemPointerData));
881 : : else
882 : 32581 : newsize = keysize;
883 : :
884 [ - + ]: 253562 : Assert(newsize <= INDEX_SIZE_MASK);
885 [ - + ]: 253562 : Assert(newsize == MAXALIGN(newsize));
886 : :
887 : : /* Allocate memory using palloc0() (matches index_form_tuple()) */
888 : 253562 : itup = palloc0(newsize);
889 : 253562 : memcpy(itup, base, keysize);
890 : 253562 : itup->t_info &= ~INDEX_SIZE_MASK;
891 : 253562 : itup->t_info |= newsize;
892 [ + + ]: 253562 : if (nhtids > 1)
893 : : {
894 : : /* Form posting list tuple */
895 : 220981 : BTreeTupleSetPosting(itup, nhtids, keysize);
896 : 220981 : memcpy(BTreeTupleGetPosting(itup), htids,
897 : : sizeof(ItemPointerData) * nhtids);
898 [ - + ]: 220981 : Assert(_bt_posting_valid(itup));
899 : : }
900 : : else
901 : : {
902 : : /* Form standard non-pivot tuple */
903 : 32581 : itup->t_info &= ~INDEX_ALT_TID_MASK;
904 : 32581 : ItemPointerCopy(htids, &itup->t_tid);
905 [ - + ]: 32581 : Assert(ItemPointerIsValid(&itup->t_tid));
906 : : }
907 : :
908 : 253562 : return itup;
909 : : }
910 : :
911 : : /*
912 : : * Generate a replacement tuple by "updating" a posting list tuple so that it
913 : : * no longer has TIDs that need to be deleted.
914 : : *
915 : : * Used by both VACUUM and index deletion. Caller's vacposting argument
916 : : * points to the existing posting list tuple to be updated.
917 : : *
918 : : * On return, caller's vacposting argument will point to final "updated"
919 : : * tuple, which will be palloc()'d in caller's memory context.
920 : : */
921 : : void
922 : 31416 : _bt_update_posting(BTVacuumPosting vacposting)
923 : : {
924 : 31416 : IndexTuple origtuple = vacposting->itup;
925 : : uint32 keysize,
926 : : newsize;
927 : : IndexTuple itup;
928 : : int nhtids;
929 : : int ui,
930 : : d;
931 : : ItemPointer htids;
932 : :
933 : 31416 : nhtids = BTreeTupleGetNPosting(origtuple) - vacposting->ndeletedtids;
934 : :
935 [ - + ]: 31416 : Assert(_bt_posting_valid(origtuple));
936 [ + - - + ]: 31416 : Assert(nhtids > 0 && nhtids < BTreeTupleGetNPosting(origtuple));
937 : :
938 : : /*
939 : : * Determine final size of new tuple.
940 : : *
941 : : * This calculation needs to match the code used within _bt_form_posting()
942 : : * for new posting list tuples. We avoid calling _bt_form_posting() here
943 : : * to save ourselves a second memory allocation for a htids workspace.
944 : : */
2067 945 : 31416 : keysize = BTreeTupleGetPostingOffset(origtuple);
2071 946 [ + + ]: 31416 : if (nhtids > 1)
947 : 5138 : newsize = MAXALIGN(keysize +
948 : : nhtids * sizeof(ItemPointerData));
949 : : else
950 : 26278 : newsize = keysize;
951 : :
2066 952 [ - + ]: 31416 : Assert(newsize <= INDEX_SIZE_MASK);
953 [ - + ]: 31416 : Assert(newsize == MAXALIGN(newsize));
954 : :
955 : : /* Allocate memory using palloc0() (matches index_form_tuple()) */
2071 956 : 31416 : itup = palloc0(newsize);
957 : 31416 : memcpy(itup, origtuple, keysize);
958 : 31416 : itup->t_info &= ~INDEX_SIZE_MASK;
959 : 31416 : itup->t_info |= newsize;
960 : :
961 [ + + ]: 31416 : if (nhtids > 1)
962 : : {
963 : : /* Form posting list tuple */
964 : 5138 : BTreeTupleSetPosting(itup, nhtids, keysize);
965 : 5138 : htids = BTreeTupleGetPosting(itup);
966 : : }
967 : : else
968 : : {
969 : : /* Form standard non-pivot tuple */
970 : 26278 : itup->t_info &= ~INDEX_ALT_TID_MASK;
971 : 26278 : htids = &itup->t_tid;
972 : : }
973 : :
974 : 31416 : ui = 0;
975 : 31416 : d = 0;
976 [ + + ]: 173517 : for (int i = 0; i < BTreeTupleGetNPosting(origtuple); i++)
977 : : {
978 [ + + + + ]: 142101 : if (d < vacposting->ndeletedtids && vacposting->deletetids[d] == i)
979 : : {
980 : 73203 : d++;
981 : 73203 : continue;
982 : : }
983 : 68898 : htids[ui++] = *BTreeTupleGetPostingN(origtuple, i);
984 : : }
985 [ - + ]: 31416 : Assert(ui == nhtids);
986 [ - + ]: 31416 : Assert(d == vacposting->ndeletedtids);
987 [ + + - + ]: 31416 : Assert(nhtids == 1 || _bt_posting_valid(itup));
2066 988 [ + + - + ]: 31416 : Assert(nhtids > 1 || ItemPointerIsValid(&itup->t_tid));
989 : :
990 : : /* vacposting arg's itup will now point to updated version */
2071 991 : 31416 : vacposting->itup = itup;
992 : 31416 : }
993 : :
994 : : /*
995 : : * Prepare for a posting list split by swapping heap TID in newitem with heap
996 : : * TID from original posting list (the 'oposting' heap TID located at offset
997 : : * 'postingoff'). Modifies newitem, so caller should pass their own private
998 : : * copy that can safely be modified.
999 : : *
1000 : : * Returns new posting list tuple, which is palloc()'d in caller's context.
1001 : : * This is guaranteed to be the same size as 'oposting'. Modified newitem is
1002 : : * what caller actually inserts. (This happens inside the same critical
1003 : : * section that performs an in-place update of old posting list using new
1004 : : * posting list returned here.)
1005 : : *
1006 : : * While the keys from newitem and oposting must be opclass equal, and must
1007 : : * generate identical output when run through the underlying type's output
1008 : : * function, it doesn't follow that their representations match exactly.
1009 : : * Caller must avoid assuming that there can't be representational differences
1010 : : * that make datums from oposting bigger or smaller than the corresponding
1011 : : * datums from newitem. For example, differences in TOAST input state might
1012 : : * break a faulty assumption about tuple size (the executor is entitled to
1013 : : * apply TOAST compression based on its own criteria). It also seems possible
1014 : : * that further representational variation will be introduced in the future,
1015 : : * in order to support nbtree features like page-level prefix compression.
1016 : : *
1017 : : * See nbtree/README for details on the design of posting list splits.
1018 : : */
1019 : : IndexTuple
1020 : 17851 : _bt_swap_posting(IndexTuple newitem, IndexTuple oposting, int postingoff)
1021 : : {
1022 : : int nhtids;
1023 : : char *replacepos;
1024 : : char *replaceposright;
1025 : : Size nmovebytes;
1026 : : IndexTuple nposting;
1027 : :
1028 : 17851 : nhtids = BTreeTupleGetNPosting(oposting);
1029 [ - + ]: 17851 : Assert(_bt_posting_valid(oposting));
1030 : :
1031 : : /*
1032 : : * The postingoff argument originated as a _bt_binsrch_posting() return
1033 : : * value. It will be 0 in the event of corruption that makes a leaf page
1034 : : * contain a non-pivot tuple that's somehow identical to newitem (no two
1035 : : * non-pivot tuples should ever have the same TID). This has been known
1036 : : * to happen in the field from time to time.
1037 : : *
1038 : : * Perform a basic sanity check to catch this case now.
1039 : : */
1628 1040 [ + - - + ]: 17851 : if (!(postingoff > 0 && postingoff < nhtids))
1628 pg@bowt.ie 1041 [ # # ]:UBC 0 : elog(ERROR, "posting list tuple with %d items cannot be split at offset %d",
1042 : : nhtids, postingoff);
1043 : :
1044 : : /*
1045 : : * Move item pointers in posting list to make a gap for the new item's
1046 : : * heap TID. We shift TIDs one place to the right, losing original
1047 : : * rightmost TID. (nmovebytes must not include TIDs to the left of
1048 : : * postingoff, nor the existing rightmost/max TID that gets overwritten.)
1049 : : */
2071 pg@bowt.ie 1050 :CBC 17851 : nposting = CopyIndexTuple(oposting);
1051 : 17851 : replacepos = (char *) BTreeTupleGetPostingN(nposting, postingoff);
1052 : 17851 : replaceposright = (char *) BTreeTupleGetPostingN(nposting, postingoff + 1);
1053 : 17851 : nmovebytes = (nhtids - postingoff - 1) * sizeof(ItemPointerData);
1054 : 17851 : memmove(replaceposright, replacepos, nmovebytes);
1055 : :
1056 : : /* Fill the gap at postingoff with TID of new item (original new TID) */
1057 [ + - - + ]: 17851 : Assert(!BTreeTupleIsPivot(newitem) && !BTreeTupleIsPosting(newitem));
1058 : 17851 : ItemPointerCopy(&newitem->t_tid, (ItemPointer) replacepos);
1059 : :
1060 : : /* Now copy oposting's rightmost/max TID into new item (final new TID) */
1061 : 17851 : ItemPointerCopy(BTreeTupleGetMaxHeapTID(oposting), &newitem->t_tid);
1062 : :
1063 [ - + ]: 17851 : Assert(ItemPointerCompare(BTreeTupleGetMaxHeapTID(nposting),
1064 : : BTreeTupleGetHeapTID(newitem)) < 0);
1065 [ - + ]: 17851 : Assert(_bt_posting_valid(nposting));
1066 : :
1067 : 17851 : return nposting;
1068 : : }
1069 : :
1070 : : /*
1071 : : * Verify posting list invariants for "posting", which must be a posting list
1072 : : * tuple. Used within assertions.
1073 : : */
1074 : : #ifdef USE_ASSERT_CHECKING
1075 : : static bool
1076 : 402955 : _bt_posting_valid(IndexTuple posting)
1077 : : {
1078 : : ItemPointerData last;
1079 : : ItemPointer htid;
1080 : :
1081 [ + - - + ]: 402955 : if (!BTreeTupleIsPosting(posting) || BTreeTupleGetNPosting(posting) < 2)
2071 pg@bowt.ie 1082 :UBC 0 : return false;
1083 : :
1084 : : /* Remember first heap TID for loop */
2071 pg@bowt.ie 1085 :CBC 402955 : ItemPointerCopy(BTreeTupleGetHeapTID(posting), &last);
1086 [ - + ]: 402955 : if (!ItemPointerIsValid(&last))
2071 pg@bowt.ie 1087 :UBC 0 : return false;
1088 : :
1089 : : /* Iterate, starting from second TID */
2071 pg@bowt.ie 1090 [ + + ]:CBC 8034359 : for (int i = 1; i < BTreeTupleGetNPosting(posting); i++)
1091 : : {
1092 : 7631404 : htid = BTreeTupleGetPostingN(posting, i);
1093 : :
1094 [ - + ]: 7631404 : if (!ItemPointerIsValid(htid))
2071 pg@bowt.ie 1095 :UBC 0 : return false;
2071 pg@bowt.ie 1096 [ - + ]:CBC 7631404 : if (ItemPointerCompare(htid, &last) <= 0)
2071 pg@bowt.ie 1097 :UBC 0 : return false;
2071 pg@bowt.ie 1098 :CBC 7631404 : ItemPointerCopy(htid, &last);
1099 : : }
1100 : :
1101 : 402955 : return true;
1102 : : }
1103 : : #endif
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