btr0pcur.cc 18.8 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637
/*****************************************************************************

Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
Copyright (c) 2016, 2019, MariaDB Corporation.

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; version 2 of the License.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA

*****************************************************************************/

/**************************************************//**
@file btr/btr0pcur.cc
The index tree persistent cursor

Created 2/23/1996 Heikki Tuuri
*******************************************************/

#include "btr0pcur.h"
#include "ut0byte.h"
#include "rem0cmp.h"
#include "trx0trx.h"

/**************************************************************//**
Allocates memory for a persistent cursor object and initializes the cursor.
@return own: persistent cursor */
btr_pcur_t*
btr_pcur_create_for_mysql(void)
/*============================*/
{
	btr_pcur_t*	pcur;
	DBUG_ENTER("btr_pcur_create_for_mysql");

	pcur = (btr_pcur_t*) ut_malloc_nokey(sizeof(btr_pcur_t));

	pcur->btr_cur.index = NULL;
	btr_pcur_init(pcur);

	DBUG_PRINT("btr_pcur_create_for_mysql", ("pcur: %p", pcur));
	DBUG_RETURN(pcur);
}

/**************************************************************//**
Resets a persistent cursor object, freeing ::old_rec_buf if it is
allocated and resetting the other members to their initial values. */
void
btr_pcur_reset(
/*===========*/
	btr_pcur_t*	cursor)	/*!< in, out: persistent cursor */
{
	btr_pcur_free(cursor);
	cursor->old_rec_buf = NULL;
	cursor->btr_cur.index = NULL;
	cursor->btr_cur.page_cur.rec = NULL;
	cursor->old_rec = NULL;
	cursor->old_n_fields = 0;
	cursor->old_stored = false;

	cursor->latch_mode = BTR_NO_LATCHES;
	cursor->pos_state = BTR_PCUR_NOT_POSITIONED;
}

/**************************************************************//**
Frees the memory for a persistent cursor object. */
void
btr_pcur_free_for_mysql(
/*====================*/
	btr_pcur_t*	cursor)	/*!< in, own: persistent cursor */
{
	DBUG_ENTER("btr_pcur_free_for_mysql");
	DBUG_PRINT("btr_pcur_free_for_mysql", ("pcur: %p", cursor));

	btr_pcur_free(cursor);
	ut_free(cursor);
	DBUG_VOID_RETURN;
}

/**************************************************************//**
The position of the cursor is stored by taking an initial segment of the
record the cursor is positioned on, before, or after, and copying it to the
cursor data structure, or just setting a flag if the cursor id before the
first in an EMPTY tree, or after the last in an EMPTY tree. NOTE that the
page where the cursor is positioned must not be empty if the index tree is
not totally empty! */
void
btr_pcur_store_position(
/*====================*/
	btr_pcur_t*	cursor, /*!< in: persistent cursor */
	mtr_t*		mtr)	/*!< in: mtr */
{
	page_cur_t*	page_cursor;
	buf_block_t*	block;
	rec_t*		rec;
	dict_index_t*	index;
	ulint		offs;

	ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
	ut_ad(cursor->latch_mode != BTR_NO_LATCHES);

	block = btr_pcur_get_block(cursor);
	index = btr_cur_get_index(btr_pcur_get_btr_cur(cursor));

	page_cursor = btr_pcur_get_page_cur(cursor);

	rec = page_cur_get_rec(page_cursor);
	offs = rec - block->frame;
	ut_ad(block->page.id.page_no() == page_get_page_no(block->frame));
	ut_ad(block->page.buf_fix_count);
	/* For spatial index, when we do positioning on parent
	buffer if necessary, it might not hold latches, but the
	tree must be locked to prevent change on the page */
	ut_ad(mtr_memo_contains_flagged(mtr, block,
					MTR_MEMO_PAGE_S_FIX
					| MTR_MEMO_PAGE_X_FIX)
	      || (dict_index_is_spatial(index)
		  && mtr_memo_contains_flagged(
			  mtr, dict_index_get_lock(index),
			  MTR_MEMO_X_LOCK | MTR_MEMO_SX_LOCK)));

	cursor->old_stored = true;

	if (page_is_empty(block->frame)) {
		/* It must be an empty index tree; NOTE that in this case
		we do not store the modify_clock, but always do a search
		if we restore the cursor position */

		ut_a(!page_has_siblings(block->frame));
		ut_ad(page_is_leaf(block->frame));
		ut_ad(block->page.id.page_no() == index->page);

		if (page_rec_is_supremum_low(offs)) {
			cursor->rel_pos = BTR_PCUR_AFTER_LAST_IN_TREE;
		} else {
before_first:
			cursor->rel_pos = BTR_PCUR_BEFORE_FIRST_IN_TREE;
		}

		return;
	}

	if (page_rec_is_supremum_low(offs)) {
		rec = page_rec_get_prev(rec);

		ut_ad(!page_rec_is_infimum(rec));
		if (UNIV_UNLIKELY(rec_is_metadata(rec, *index))) {
			ut_ad(index->table->instant);
			ut_ad(page_get_n_recs(block->frame) == 1);
			ut_ad(page_is_leaf(block->frame));
			ut_ad(page_get_page_no(block->frame) == index->page);
			cursor->rel_pos = BTR_PCUR_AFTER_LAST_IN_TREE;
			return;
		}

		cursor->rel_pos = BTR_PCUR_AFTER;
	} else if (page_rec_is_infimum_low(offs)) {
		rec = page_rec_get_next(rec);

		if (rec_is_metadata(rec, *index)) {
			ut_ad(!page_has_prev(block->frame));
			ut_d(const rec_t* p = rec);
			rec = page_rec_get_next(rec);
			if (page_rec_is_supremum(rec)) {
				ut_ad(page_has_next(block->frame)
				      || rec_is_alter_metadata(p, *index));
				goto before_first;
			}
		}

		cursor->rel_pos = BTR_PCUR_BEFORE;
	} else {
		cursor->rel_pos = BTR_PCUR_ON;
	}

	if (index->is_ibuf()) {
		ut_ad(!index->table->not_redundant());
		cursor->old_n_fields = rec_get_n_fields_old(rec);
	} else if (page_rec_is_leaf(rec)) {
		cursor->old_n_fields = dict_index_get_n_unique_in_tree(index);
	} else if (index->is_spatial()) {
		ut_ad(dict_index_get_n_unique_in_tree_nonleaf(index)
		      == DICT_INDEX_SPATIAL_NODEPTR_SIZE);
		/* For R-tree, we have to compare
		the child page numbers as well. */
		cursor->old_n_fields = DICT_INDEX_SPATIAL_NODEPTR_SIZE + 1;
	} else {
		cursor->old_n_fields = dict_index_get_n_unique_in_tree(index);
	}

	cursor->old_rec = rec_copy_prefix_to_buf(rec, index,
						 cursor->old_n_fields,
						 &cursor->old_rec_buf,
						 &cursor->buf_size);
	cursor->block_when_stored = block;

	/* Function try to check if block is S/X latch. */
	cursor->modify_clock = buf_block_get_modify_clock(block);
	cursor->withdraw_clock = buf_withdraw_clock;
}

/**************************************************************//**
Copies the stored position of a pcur to another pcur. */
void
btr_pcur_copy_stored_position(
/*==========================*/
	btr_pcur_t*	pcur_receive,	/*!< in: pcur which will receive the
					position info */
	btr_pcur_t*	pcur_donate)	/*!< in: pcur from which the info is
					copied */
{
	ut_free(pcur_receive->old_rec_buf);
	ut_memcpy(pcur_receive, pcur_donate, sizeof(btr_pcur_t));

	if (pcur_donate->old_rec_buf) {

		pcur_receive->old_rec_buf = (byte*)
			ut_malloc_nokey(pcur_donate->buf_size);

		ut_memcpy(pcur_receive->old_rec_buf, pcur_donate->old_rec_buf,
			  pcur_donate->buf_size);
		pcur_receive->old_rec = pcur_receive->old_rec_buf
			+ (pcur_donate->old_rec - pcur_donate->old_rec_buf);
	}

	pcur_receive->old_n_fields = pcur_donate->old_n_fields;
}

/**************************************************************//**
Restores the stored position of a persistent cursor bufferfixing the page and
obtaining the specified latches. If the cursor position was saved when the
(1) cursor was positioned on a user record: this function restores the position
to the last record LESS OR EQUAL to the stored record;
(2) cursor was positioned on a page infimum record: restores the position to
the last record LESS than the user record which was the successor of the page
infimum;
(3) cursor was positioned on the page supremum: restores to the first record
GREATER than the user record which was the predecessor of the supremum.
(4) cursor was positioned before the first or after the last in an empty tree:
restores to before first or after the last in the tree.
@return TRUE if the cursor position was stored when it was on a user
record and it can be restored on a user record whose ordering fields
are identical to the ones of the original user record */
ibool
btr_pcur_restore_position_func(
/*===========================*/
	ulint		latch_mode,	/*!< in: BTR_SEARCH_LEAF, ... */
	btr_pcur_t*	cursor,		/*!< in: detached persistent cursor */
	const char*	file,		/*!< in: file name */
	unsigned	line,		/*!< in: line where called */
	mtr_t*		mtr)		/*!< in: mtr */
{
	dict_index_t*	index;
	dtuple_t*	tuple;
	page_cur_mode_t	mode;
	page_cur_mode_t	old_mode;
	mem_heap_t*	heap;

	ut_ad(mtr->is_active());
	//ut_ad(cursor->old_stored);
	ut_ad(cursor->pos_state == BTR_PCUR_WAS_POSITIONED
	      || cursor->pos_state == BTR_PCUR_IS_POSITIONED);

	index = btr_cur_get_index(btr_pcur_get_btr_cur(cursor));

	if (UNIV_UNLIKELY
	    (cursor->rel_pos == BTR_PCUR_AFTER_LAST_IN_TREE
	     || cursor->rel_pos == BTR_PCUR_BEFORE_FIRST_IN_TREE)) {
		dberr_t err = DB_SUCCESS;

		/* In these cases we do not try an optimistic restoration,
		but always do a search */

		err = btr_cur_open_at_index_side(
			cursor->rel_pos == BTR_PCUR_BEFORE_FIRST_IN_TREE,
			index, latch_mode,
			btr_pcur_get_btr_cur(cursor), 0, mtr);

		if (err != DB_SUCCESS) {
			ib::warn() << " Error code: " << err
				   << " btr_pcur_restore_position_func "
				   << " called from file: "
				   << file << " line: " << line
				   << " table: " << index->table->name
				   << " index: " << index->name;
		}

		cursor->latch_mode =
			BTR_LATCH_MODE_WITHOUT_INTENTION(latch_mode);
		cursor->pos_state = BTR_PCUR_IS_POSITIONED;
		cursor->block_when_stored = btr_pcur_get_block(cursor);

		return(FALSE);
	}

	ut_a(cursor->old_rec);
	ut_a(cursor->old_n_fields);

	switch (latch_mode) {
	case BTR_SEARCH_LEAF:
	case BTR_MODIFY_LEAF:
	case BTR_SEARCH_PREV:
	case BTR_MODIFY_PREV:
		/* Try optimistic restoration. */

		if (!buf_pool_is_obsolete(cursor->withdraw_clock)
		    && btr_cur_optimistic_latch_leaves(
			cursor->block_when_stored, cursor->modify_clock,
			&latch_mode, btr_pcur_get_btr_cur(cursor),
			file, line, mtr)) {

			cursor->pos_state = BTR_PCUR_IS_POSITIONED;
			cursor->latch_mode = latch_mode;

			buf_block_dbg_add_level(
				btr_pcur_get_block(cursor),
				dict_index_is_ibuf(index)
				? SYNC_IBUF_TREE_NODE : SYNC_TREE_NODE);

			if (cursor->rel_pos == BTR_PCUR_ON) {
#ifdef UNIV_DEBUG
				const rec_t*	rec;
				const ulint*	offsets1;
				const ulint*	offsets2;
				rec = btr_pcur_get_rec(cursor);

				heap = mem_heap_create(256);
				offsets1 = rec_get_offsets(
					cursor->old_rec, index, NULL, true,
					cursor->old_n_fields, &heap);
				offsets2 = rec_get_offsets(
					rec, index, NULL, true,
					cursor->old_n_fields, &heap);

				ut_ad(!cmp_rec_rec(cursor->old_rec,
						   rec, offsets1, offsets2,
						   index));
				mem_heap_free(heap);
#endif /* UNIV_DEBUG */
				return(TRUE);
			}
			/* This is the same record as stored,
			may need to be adjusted for BTR_PCUR_BEFORE/AFTER,
			depending on search mode and direction. */
			if (btr_pcur_is_on_user_rec(cursor)) {
				cursor->pos_state
					= BTR_PCUR_IS_POSITIONED_OPTIMISTIC;
			}
			return(FALSE);
		}
	}

	/* If optimistic restoration did not succeed, open the cursor anew */

	heap = mem_heap_create(256);

	tuple = dict_index_build_data_tuple(cursor->old_rec, index, true,
					    cursor->old_n_fields, heap);

	/* Save the old search mode of the cursor */
	old_mode = cursor->search_mode;

	switch (cursor->rel_pos) {
	case BTR_PCUR_ON:
		mode = PAGE_CUR_LE;
		break;
	case BTR_PCUR_AFTER:
		mode = PAGE_CUR_G;
		break;
	case BTR_PCUR_BEFORE:
		mode = PAGE_CUR_L;
		break;
	default:
		ut_error;
		mode = PAGE_CUR_UNSUPP;
	}

	btr_pcur_open_with_no_init_func(index, tuple, mode, latch_mode,
					cursor,
#ifdef BTR_CUR_HASH_ADAPT
					NULL,
#endif /* BTR_CUR_HASH_ADAPT */
					file, line, mtr);

	/* Restore the old search mode */
	cursor->search_mode = old_mode;

	ut_ad(cursor->rel_pos == BTR_PCUR_ON
	      || cursor->rel_pos == BTR_PCUR_BEFORE
	      || cursor->rel_pos == BTR_PCUR_AFTER);
	if (cursor->rel_pos == BTR_PCUR_ON
	    && btr_pcur_is_on_user_rec(cursor)
	    && !cmp_dtuple_rec(tuple, btr_pcur_get_rec(cursor),
			       rec_get_offsets(btr_pcur_get_rec(cursor),
					       index, NULL, true,
					       ULINT_UNDEFINED, &heap))) {

		/* We have to store the NEW value for the modify clock,
		since the cursor can now be on a different page!
		But we can retain the value of old_rec */

		cursor->block_when_stored = btr_pcur_get_block(cursor);
		cursor->modify_clock = buf_block_get_modify_clock(
						cursor->block_when_stored);
		cursor->old_stored = true;
		cursor->withdraw_clock = buf_withdraw_clock;

		mem_heap_free(heap);

		return(TRUE);
	}

	mem_heap_free(heap);

	/* We have to store new position information, modify_clock etc.,
	to the cursor because it can now be on a different page, the record
	under it may have been removed, etc. */

	btr_pcur_store_position(cursor, mtr);

	return(FALSE);
}

/*********************************************************//**
Moves the persistent cursor to the first record on the next page. Releases the
latch on the current page, and bufferunfixes it. Note that there must not be
modifications on the current page, as then the x-latch can be released only in
mtr_commit. */
void
btr_pcur_move_to_next_page(
/*=======================*/
	btr_pcur_t*	cursor,	/*!< in: persistent cursor; must be on the
				last record of the current page */
	mtr_t*		mtr)	/*!< in: mtr */
{
	ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
	ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
	ut_ad(btr_pcur_is_after_last_on_page(cursor));

	cursor->old_stored = false;

	const page_t* page = btr_pcur_get_page(cursor);

	if (UNIV_UNLIKELY(!page)) {
		return;
	}

	const ulint next_page_no = mach_read_from_4(page + FIL_PAGE_NEXT);

	ut_ad(next_page_no != FIL_NULL);

	ulint mode = cursor->latch_mode;
	switch (mode) {
	case BTR_SEARCH_TREE:
		mode = BTR_SEARCH_LEAF;
		break;
	case BTR_MODIFY_TREE:
		mode = BTR_MODIFY_LEAF;
	}

	buf_block_t* next_block = btr_block_get(
		*btr_pcur_get_btr_cur(cursor)->index, next_page_no, mode, mtr);

	if (UNIV_UNLIKELY(!next_block)) {
		return;
	}

	const page_t* next_page = buf_block_get_frame(next_block);
#ifdef UNIV_BTR_DEBUG
	ut_a(page_is_comp(next_page) == page_is_comp(page));
	ut_a(btr_page_get_prev(next_page, mtr)
	     == btr_pcur_get_block(cursor)->page.id.page_no());
#endif /* UNIV_BTR_DEBUG */

	btr_leaf_page_release(btr_pcur_get_block(cursor), mode, mtr);

	page_cur_set_before_first(next_block, btr_pcur_get_page_cur(cursor));

	ut_d(page_check_dir(next_page));
}

/*********************************************************//**
Moves the persistent cursor backward if it is on the first record of the page.
Commits mtr. Note that to prevent a possible deadlock, the operation
first stores the position of the cursor, commits mtr, acquires the necessary
latches and restores the cursor position again before returning. The
alphabetical position of the cursor is guaranteed to be sensible on
return, but it may happen that the cursor is not positioned on the last
record of any page, because the structure of the tree may have changed
during the time when the cursor had no latches. */
static
void
btr_pcur_move_backward_from_page(
/*=============================*/
	btr_pcur_t*	cursor,	/*!< in: persistent cursor, must be on the first
				record of the current page */
	mtr_t*		mtr)	/*!< in: mtr */
{
	ulint		prev_page_no;
	page_t*		page;
	buf_block_t*	prev_block;
	ulint		latch_mode;
	ulint		latch_mode2;

	ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
	ut_ad(btr_pcur_is_before_first_on_page(cursor));
	ut_ad(!btr_pcur_is_before_first_in_tree(cursor));

	latch_mode = cursor->latch_mode;

	if (latch_mode == BTR_SEARCH_LEAF) {

		latch_mode2 = BTR_SEARCH_PREV;

	} else if (latch_mode == BTR_MODIFY_LEAF) {

		latch_mode2 = BTR_MODIFY_PREV;
	} else {
		latch_mode2 = 0; /* To eliminate compiler warning */
		ut_error;
	}

	btr_pcur_store_position(cursor, mtr);

	mtr_commit(mtr);

	mtr_start(mtr);

	btr_pcur_restore_position(latch_mode2, cursor, mtr);

	page = btr_pcur_get_page(cursor);

	prev_page_no = btr_page_get_prev(page, mtr);

	if (prev_page_no == FIL_NULL) {
	} else if (btr_pcur_is_before_first_on_page(cursor)) {

		prev_block = btr_pcur_get_btr_cur(cursor)->left_block;

		btr_leaf_page_release(btr_pcur_get_block(cursor),
				      latch_mode, mtr);

		page_cur_set_after_last(prev_block,
					btr_pcur_get_page_cur(cursor));
	} else {

		/* The repositioned cursor did not end on an infimum
		record on a page. Cursor repositioning acquired a latch
		also on the previous page, but we do not need the latch:
		release it. */

		prev_block = btr_pcur_get_btr_cur(cursor)->left_block;

		btr_leaf_page_release(prev_block, latch_mode, mtr);
	}

	cursor->latch_mode = latch_mode;
	cursor->old_stored = false;
}

/*********************************************************//**
Moves the persistent cursor to the previous record in the tree. If no records
are left, the cursor stays 'before first in tree'.
@return TRUE if the cursor was not before first in tree */
ibool
btr_pcur_move_to_prev(
/*==================*/
	btr_pcur_t*	cursor,	/*!< in: persistent cursor; NOTE that the
				function may release the page latch */
	mtr_t*		mtr)	/*!< in: mtr */
{
	ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
	ut_ad(cursor->latch_mode != BTR_NO_LATCHES);

	cursor->old_stored = false;

	if (btr_pcur_is_before_first_on_page(cursor)) {

		if (btr_pcur_is_before_first_in_tree(cursor)) {

			return(FALSE);
		}

		btr_pcur_move_backward_from_page(cursor, mtr);

		return(TRUE);
	}

	btr_pcur_move_to_prev_on_page(cursor);

	return(TRUE);
}

/**************************************************************//**
If mode is PAGE_CUR_G or PAGE_CUR_GE, opens a persistent cursor on the first
user record satisfying the search condition, in the case PAGE_CUR_L or
PAGE_CUR_LE, on the last user record. If no such user record exists, then
in the first case sets the cursor after last in tree, and in the latter case
before first in tree. The latching mode must be BTR_SEARCH_LEAF or
BTR_MODIFY_LEAF. */
void
btr_pcur_open_on_user_rec_func(
/*===========================*/
	dict_index_t*	index,		/*!< in: index */
	const dtuple_t*	tuple,		/*!< in: tuple on which search done */
	page_cur_mode_t	mode,		/*!< in: PAGE_CUR_L, ... */
	ulint		latch_mode,	/*!< in: BTR_SEARCH_LEAF or
					BTR_MODIFY_LEAF */
	btr_pcur_t*	cursor,		/*!< in: memory buffer for persistent
					cursor */
	const char*	file,		/*!< in: file name */
	unsigned	line,		/*!< in: line where called */
	mtr_t*		mtr)		/*!< in: mtr */
{
	btr_pcur_open_low(index, 0, tuple, mode, latch_mode, cursor,
			  file, line, 0, mtr);

	if ((mode == PAGE_CUR_GE) || (mode == PAGE_CUR_G)) {

		if (btr_pcur_is_after_last_on_page(cursor)) {

			btr_pcur_move_to_next_user_rec(cursor, mtr);
		}
	} else {
		ut_ad((mode == PAGE_CUR_LE) || (mode == PAGE_CUR_L));

		/* Not implemented yet */

		ut_error;
	}
}