path: root/innobase/btr/btr0sea.c

/************************************************************************
The index tree adaptive search

(c) 1996 Innobase Oy

Created 2/17/1996 Heikki Tuuri
*************************************************************************/

#include "btr0sea.h"
#ifdef UNIV_NONINL
#include "btr0sea.ic"
#endif

#include "buf0buf.h"
#include "page0page.h"
#include "page0cur.h"
#include "btr0cur.h"
#include "btr0btr.h"

ulint	btr_search_n_succ	= 0;
ulint	btr_search_n_hash_fail	= 0;

byte	btr_sea_pad1[64];	/* padding to prevent other memory update
				hotspots from residing on the same memory
				cache line as btr_search_latch */

/* The latch protecting the adaptive search system: this latch protects the
(1) positions of records on those pages where a hash index has been built.
NOTE: It does not protect values of non-ordering fields within a record from
being updated in-place! We can use fact (1) to perform unique searches to
indexes. */

rw_lock_t*	btr_search_latch_temp; /* We will allocate the latch from
					dynamic memory to get it to the
					same DRAM page as other hotspot
					semaphores */

byte	btr_sea_pad2[64];	/* padding to prevent other memory update
				hotspots from residing on the same memory
				cache line */

btr_search_sys_t*	btr_search_sys;

/* If the number of records on the page divided by this parameter
would have been successfully accessed using a hash index, the index
is then built on the page, assuming the global limit has been reached */

#define BTR_SEARCH_PAGE_BUILD_LIMIT	16

/* The global limit for consecutive potentially successful hash searches,
before hash index building is started */

#define BTR_SEARCH_BUILD_LIMIT		100

/************************************************************************
Builds a hash index on a page with the given parameters. If the page already
has a hash index with different parameters, the old hash index is removed. */
static
void
btr_search_build_page_hash_index(
/*=============================*/
	page_t*	page,		/* in: index page, s- or x-latched */
	ulint	n_fields,	/* in: hash this many full fields */
	ulint	n_bytes,	/* in: hash this many bytes from the next
				field */
	ulint	side);		/* in: hash for searches from this side */

/*********************************************************************
This function should be called before reserving any btr search mutex, if
the intended operation might add nodes to the search system hash table.
Because of the latching order, once we have reserved the btr search system
latch, we cannot allocate a free frame from the buffer pool. Checks that
there is a free buffer frame allocated for hash table heap in the btr search
system. If not, allocates a free frames for the heap. This check makes it
probable that, when have reserved the btr search system latch and we need to
allocate a new node to the hash table, it will succeed. However, the check
will not guarantee success. */
static
void
btr_search_check_free_space_in_heap(void)
/*=====================================*/
{
	buf_frame_t*	frame;
	hash_table_t*	table;
	mem_heap_t*	heap;

	ut_ad(!rw_lock_own(&btr_search_latch, RW_LOCK_SHARED)
			&& !rw_lock_own(&btr_search_latch, RW_LOCK_EX));

	table = btr_search_sys->hash_index;

	heap = table->heap;
			
	/* Note that we peek the value of heap->free_block without reserving
	the latch: this is ok, because we will not guarantee that there will
	be enough free space in the hash table. */

	if (heap->free_block == NULL) {
		frame = buf_frame_alloc();

		rw_lock_x_lock(&btr_search_latch);

		if (heap->free_block == NULL) {
			heap->free_block = frame;
		} else {
			buf_frame_free(frame);
		}

		rw_lock_x_unlock(&btr_search_latch);
	}
}

/*********************************************************************
Creates and initializes the adaptive search system at a database start. */

void
btr_search_sys_create(
/*==================*/
	ulint	hash_size)	/* in: hash index hash table size */
{
	/* We allocate the search latch from dynamic memory:
	see above at the global variable definition */
	
	btr_search_latch_temp = mem_alloc(sizeof(rw_lock_t));
	
	rw_lock_create(&btr_search_latch);

	btr_search_sys = mem_alloc(sizeof(btr_search_sys_t));

	btr_search_sys->hash_index = ha_create(TRUE, hash_size, 0, 0);

	rw_lock_set_level(&btr_search_latch, SYNC_SEARCH_SYS);
}

/*********************************************************************
Creates and initializes a search info struct. */

btr_search_t*
btr_search_info_create(
/*===================*/
				/* out, own: search info struct */
	mem_heap_t*	heap)	/* in: heap where created */
{
	btr_search_t*	info;

	info = mem_heap_alloc(heap, sizeof(btr_search_t));

	info->last_search = NULL;
	info->n_direction = 0;
	info->root_guess = NULL;

	info->hash_analysis = 0;
	info->n_hash_potential = 0;

	info->last_hash_succ = FALSE;

	info->n_hash_succ = 0;	
	info->n_hash_fail = 0;	
	info->n_patt_succ = 0;	
	info->n_searches = 0;	

	return(info);
}

/*************************************************************************
Updates the search info of an index about hash successes. */
static
void
btr_search_info_update_hash(
/*========================*/
	btr_search_t*	info,	/* in: search info */
	btr_cur_t*	cursor)	/* in: cursor which was just positioned */
{
	dict_index_t*	index;
	ulint		n_unique;
	int		cmp;

	ut_ad(!rw_lock_own(&btr_search_latch, RW_LOCK_SHARED)
			&& !rw_lock_own(&btr_search_latch, RW_LOCK_EX));

	index = cursor->index;

	if (index->type & DICT_IBUF) {
		/* So many deletes are performed on an insert buffer tree
		that we do not consider a hash index useful on it: */

		return;
	}

	if (info->n_hash_potential == 0) {

		goto set_new_recomm;
	}

	n_unique = dict_index_get_n_unique_in_tree(index);

	/* Test if the search would have succeeded using the recommended
	hash prefix */

	if ((info->n_fields >= n_unique) && (cursor->up_match >= n_unique)) {
			
		info->n_hash_potential++;

		return;
	}

	cmp = ut_pair_cmp(info->n_fields, info->n_bytes,
					cursor->low_match, cursor->low_bytes);

	if (((info->side == BTR_SEARCH_LEFT_SIDE) && (cmp <= 0))
		|| ((info->side == BTR_SEARCH_RIGHT_SIDE) && (cmp > 0))) {

		goto set_new_recomm;
	}

	cmp = ut_pair_cmp(info->n_fields, info->n_bytes,
					cursor->up_match, cursor->up_bytes);

	if (((info->side == BTR_SEARCH_LEFT_SIDE) && (cmp > 0))
		|| ((info->side == BTR_SEARCH_RIGHT_SIDE) && (cmp <= 0))) {

	    	goto set_new_recomm;
	}

	info->n_hash_potential++;

	return;
	
set_new_recomm:
	/* We have to set a new recommendation; skip the hash analysis
	for a while to avoid unnecessary CPU time usage when there is no
	chance for success */
	
	info->hash_analysis = 0;
	
	if ((cursor->up_match >= n_unique)
					|| (cursor->low_match >= n_unique)) {
		info->n_fields = n_unique;
		info->n_bytes = 0;

		info->side = BTR_SEARCH_LEFT_SIDE;
	}

	cmp = ut_pair_cmp(cursor->up_match, cursor->up_bytes,
					cursor->low_match, cursor->low_bytes);
	if (cmp == 0) {
		info->n_hash_potential = 0;

	} else if (cmp > 0) {
		info->n_hash_potential = 1;

		if (cursor->up_match >= n_unique) {

			info->n_fields = n_unique;
			info->n_bytes = 0;

		} else if (cursor->low_match < cursor->up_match) {

			info->n_fields = cursor->low_match + 1;
			info->n_bytes = 0;
		} else {		
			info->n_fields = cursor->low_match;
			info->n_bytes = cursor->low_bytes + 1;
		}

		info->side = BTR_SEARCH_LEFT_SIDE;
	} else {
		info->n_hash_potential = 1;

		if (cursor->low_match >= n_unique) {

			info->n_fields = n_unique;
			info->n_bytes = 0;

		} else if (cursor->low_match > cursor->up_match) {

			info->n_fields = cursor->up_match + 1;
			info->n_bytes = 0;
		} else {		
			info->n_fields = cursor->up_match;
			info->n_bytes = cursor->up_bytes + 1;
		}

		info->side = BTR_SEARCH_RIGHT_SIDE;
	}
}
	
/*************************************************************************
Updates the block search info on hash successes. */
static
ibool
btr_search_update_block_hash_info(
/*==============================*/
				/* out: TRUE if building a (new) hash index on
				the block is recommended */
	btr_search_t*	info,	/* in: search info */
	buf_block_t*	block,	/* in: buffer block */
	btr_cur_t*	cursor)	/* in: cursor */
{
	ut_ad(!rw_lock_own(&btr_search_latch, RW_LOCK_SHARED)
			&& !rw_lock_own(&btr_search_latch, RW_LOCK_EX));
	ut_ad(rw_lock_own(&(block->lock), RW_LOCK_SHARED)
				|| rw_lock_own(&(block->lock), RW_LOCK_EX));
	ut_ad(cursor);

	info->last_hash_succ = FALSE;

	if ((block->n_hash_helps > 0)
	    && (info->n_hash_potential > 0)
	    && (block->n_fields == info->n_fields)
	    && (block->n_bytes == info->n_bytes)
	    && (block->side == info->side)) {
	
		if ((block->is_hashed)
		    && (block->curr_n_fields == info->n_fields)
		    && (block->curr_n_bytes == info->n_bytes)
		    && (block->curr_side == info->side)) {

			/* The search would presumably have succeeded using
			the hash index */
		    
			info->last_hash_succ = TRUE;
		}

		block->n_hash_helps++;
	} else {
		block->n_hash_helps = 1;
		block->n_fields = info->n_fields;
		block->n_bytes = info->n_bytes;
		block->side = info->side;
	}

	if (cursor->index->table->does_not_fit_in_memory) {
		block->n_hash_helps = 0;
	}

	if ((block->n_hash_helps > page_get_n_recs(block->frame)
	    				/ BTR_SEARCH_PAGE_BUILD_LIMIT)
	    && (info->n_hash_potential >= BTR_SEARCH_BUILD_LIMIT)) {

	    	if ((!block->is_hashed)
		    || (block->n_hash_helps
					> 2 * page_get_n_recs(block->frame))
		    || (block->n_fields != block->curr_n_fields)
		    || (block->n_bytes != block->curr_n_bytes)
		    || (block->side != block->curr_side)) {

	    		/* Build a new hash index on the page */

	    		return(TRUE);
		}
	}

	return(FALSE);
}

/*************************************************************************
Updates a hash node reference when it has been unsuccessfully used in a
search which could have succeeded with the used hash parameters. This can
happen because when building a hash index for a page, we do not check
what happens at page boundaries, and therefore there can be misleading
hash nodes. Also, collisions in the fold value can lead to misleading
references. This function lazily fixes these imperfections in the hash
index. */
static
void
btr_search_update_hash_ref(
/*=======================*/
	btr_search_t*	info,	/* in: search info */
	buf_block_t*	block,	/* in: buffer block where cursor positioned */
	btr_cur_t*	cursor)	/* in: cursor */
{
	ulint	fold;
	rec_t*	rec;
	dulint	tree_id;

	ut_ad(cursor->flag == BTR_CUR_HASH_FAIL);
	ut_ad(rw_lock_own(&btr_search_latch, RW_LOCK_EX));
	ut_ad(rw_lock_own(&(block->lock), RW_LOCK_SHARED)
				|| rw_lock_own(&(block->lock), RW_LOCK_EX));
	if (block->is_hashed
	    && (info->n_hash_potential > 0)
	    && (block->curr_n_fields == info->n_fields)
	    && (block->curr_n_bytes == info->n_bytes)
	    && (block->curr_side == info->side)) {

	    	rec = btr_cur_get_rec(cursor);

	    	if (!page_rec_is_user_rec(rec)) {

	    		return;
	    	}
	    
		tree_id = ((cursor->index)->tree)->id;

		fold = rec_fold(rec, block->curr_n_fields,
						block->curr_n_bytes, tree_id);

		ut_ad(rw_lock_own(&btr_search_latch, RW_LOCK_EX));

		ha_insert_for_fold(btr_search_sys->hash_index, fold, rec);
	}
}	
	
/*************************************************************************
Updates the search info. */

void
btr_search_info_update_slow(
/*========================*/
	btr_search_t*	info,	/* in: search info */
	btr_cur_t*	cursor)	/* in: cursor which was just positioned */
{
	buf_block_t*	block;
	ibool		build_index;

	ut_ad(!rw_lock_own(&btr_search_latch, RW_LOCK_SHARED)
			&& !rw_lock_own(&btr_search_latch, RW_LOCK_EX));

	block = buf_block_align(btr_cur_get_rec(cursor));

	btr_search_info_update_hash(info, cursor);

	build_index = btr_search_update_block_hash_info(info, block, cursor);

	if (build_index || (cursor->flag == BTR_CUR_HASH_FAIL)) {

		btr_search_check_free_space_in_heap();
	}
		
	if (cursor->flag == BTR_CUR_HASH_FAIL) {
		/* Update the hash node reference, if appropriate */

		btr_search_n_hash_fail++;

		rw_lock_x_lock(&btr_search_latch);

		btr_search_update_hash_ref(info, block, cursor);

		rw_lock_x_unlock(&btr_search_latch);
	}

	if (build_index) {		
		btr_search_build_page_hash_index(block->frame,
						block->n_fields,
						block->n_bytes,
						block->side);
	}
}

/**********************************************************************
Checks if a guessed position for a tree cursor is right. Note that if
mode is PAGE_CUR_LE, which is used in inserts, and the function returns
TRUE, then cursor->up_match and cursor->low_match both have sensible values. */
UNIV_INLINE
ibool
btr_search_check_guess(
/*===================*/
				/* out: TRUE if success */
	btr_cur_t*	cursor,	/* in: guessed cursor position */
	dtuple_t* 	tuple,	/* in: data tuple */
	ulint		mode,	/* in: PAGE_CUR_L, PAGE_CUR_LE, PAGE_CUR_G,
				or PAGE_CUR_GE */
	mtr_t*		mtr)	/* in: mtr */
{
	page_t*	page;
	rec_t*	rec;
	rec_t*	prev_rec;
	rec_t*	next_rec;
	ulint	n_unique;
	ulint	match;
	ulint	bytes;
	int	cmp;
	
	n_unique = dict_index_get_n_unique_in_tree(cursor->index);
	
	rec = btr_cur_get_rec(cursor);
	page = buf_frame_align(rec);

	ut_ad(page_rec_is_user_rec(rec));

	match = 0;
	bytes = 0;

	cmp = page_cmp_dtuple_rec_with_match(tuple, rec, &match, &bytes);

	if (mode == PAGE_CUR_GE) {
		if (cmp == 1) {

			return(FALSE);
		}

		cursor->up_match = match;

		if (match >= n_unique) {

			return(TRUE);
		}	
	} else if (mode == PAGE_CUR_LE) {
		if (cmp == -1) {

			return(FALSE);
		}

		cursor->low_match = match;

	} else if (mode == PAGE_CUR_G) {
		if (cmp != -1) {

			return(FALSE);
		}
	} else if (mode == PAGE_CUR_L) {
		if (cmp != 1) {

			return(FALSE);
		}
	}

	match = 0;
	bytes = 0;

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

		ut_ad(rec != page_get_infimum_rec(page));
		
		prev_rec = page_rec_get_prev(rec);

		if (prev_rec == page_get_infimum_rec(page)) {

	    		if (btr_page_get_prev(page, mtr) != FIL_NULL) {

				return(FALSE);
			}

			return(TRUE);
		}

		cmp = page_cmp_dtuple_rec_with_match(tuple, prev_rec,
							&match, &bytes);
		if (mode == PAGE_CUR_GE) {
			if (cmp != 1) {

				return(FALSE);
			}
		} else {
			if (cmp == -1) {

				return(FALSE);
			}
		}

		return(TRUE);
	}
		
	ut_ad(rec != page_get_supremum_rec(page));
	
	next_rec = page_rec_get_next(rec);

	if (next_rec == page_get_supremum_rec(page)) {

    		if (btr_page_get_next(page, mtr) == FIL_NULL) {

			cursor->up_match = 0;

			return(TRUE);
		}

		return(FALSE);
	}

	cmp = page_cmp_dtuple_rec_with_match(tuple, next_rec, &match, &bytes);
	
	if (mode == PAGE_CUR_LE) {
		if (cmp != -1) {

			return(FALSE);
		}

		cursor->up_match = match;
	} else {
		if (cmp == 1) {

			return(FALSE);
		}
	}

	return(TRUE);
}

/**********************************************************************
Tries to guess the right search position based on the hash search info
of the index. Note that if mode is PAGE_CUR_LE, which is used in inserts,
and the function returns TRUE, then cursor->up_match and cursor->low_match
both have sensible values. */

ibool
btr_search_guess_on_hash(
/*=====================*/
					/* out: TRUE if succeeded */	
	dict_index_t*	index,		/* in: index */
	btr_search_t*	info,		/* in: index search info */
	dtuple_t*	tuple,		/* in: logical record */
	ulint		mode,		/* in: PAGE_CUR_L, ... */
	ulint		latch_mode, 	/* in: BTR_SEARCH_LEAF, ... */
	btr_cur_t*	cursor, 	/* out: tree cursor */
	ulint		has_search_latch,/* in: latch mode the caller
					currently has on btr_search_latch:
					RW_S_LATCH, RW_X_LATCH, or 0 */
	mtr_t*		mtr)		/* in: mtr */
{
	buf_block_t*	block;
	rec_t*		rec;
	page_t*		page;
	ibool		success;
	ulint		fold;
	ulint		tuple_n_fields;
	dulint		tree_id;
#ifdef notdefined
	btr_cur_t	cursor2;
#endif
	ut_ad(index && info && tuple && cursor && mtr);
	ut_ad((latch_mode == BTR_SEARCH_LEAF)
					|| (latch_mode == BTR_MODIFY_LEAF));

	/* Note that, for efficiency, the struct info may not be protected by
	any latch here! */

	if (info->n_hash_potential == 0) {

		return(FALSE);
	}

	cursor->n_fields = info->n_fields;
	cursor->n_bytes = info->n_bytes;

	tuple_n_fields = dtuple_get_n_fields(tuple);

	if (tuple_n_fields < cursor->n_fields) {

		return(FALSE);
	}

	if ((cursor->n_bytes > 0) && (tuple_n_fields <= cursor->n_fields)) {

	    	return(FALSE);
	}

	tree_id = (index->tree)->id;

#ifdef UNIV_SEARCH_PERF_STAT
	info->n_hash_succ++;
#endif
	fold = dtuple_fold(tuple, cursor->n_fields, cursor->n_bytes, tree_id);

	cursor->fold = fold;
	cursor->flag = BTR_CUR_HASH;
	
	if (!has_search_latch) {
		rw_lock_s_lock(&btr_search_latch);
	}

	rec = ha_search_and_get_data(btr_search_sys->hash_index, fold);

	if (!rec) {
		if (!has_search_latch) {
			rw_lock_s_unlock(&btr_search_latch);
		}
		
		goto failure;
	}

	page = buf_frame_align(rec);

	if (!has_search_latch) {

		success = buf_page_get_known_nowait(latch_mode, page,
						BUF_MAKE_YOUNG,
#ifdef UNIV_SYNC_DEBUG
						__FILE__, __LINE__,
#endif
						mtr);

		rw_lock_s_unlock(&btr_search_latch);

		if (!success) {

			goto failure;
		}

		buf_page_dbg_add_level(page, SYNC_TREE_NODE_FROM_HASH);
	}

	block = buf_block_align(page);

	if (block->state == BUF_BLOCK_REMOVE_HASH) {
		if (!has_search_latch) {
	
			btr_leaf_page_release(page, latch_mode, mtr);
		}

		goto failure;
	}

	ut_ad(block->state == BUF_BLOCK_FILE_PAGE);
	ut_ad(page_rec_is_user_rec(rec));	

	btr_cur_position(index, rec, cursor);

	/* Check the validity of the guess within the page */

	if (0 != ut_dulint_cmp(tree_id, btr_page_get_index_id(page))) {

		success = FALSE;
/*
		printf("Tree id %lu, page index id %lu fold %lu\n",
				ut_dulint_get_low(tree_id),
				ut_dulint_get_low(btr_page_get_index_id(page)),
				fold);
*/				
	} else {
		success = btr_search_check_guess(cursor, tuple, mode, mtr);
	}
	
	if (!success) {
		btr_leaf_page_release(page, latch_mode, mtr);

		goto failure;
	}

	if (info->n_hash_potential < BTR_SEARCH_BUILD_LIMIT + 5) {
	
		info->n_hash_potential++;
	}

	if (info->last_hash_succ != TRUE) {
		info->last_hash_succ = TRUE;
	}
	
#ifdef notdefined
	/* These lines of code can be used in a debug version to check
	correctness of the searched cursor position: */
	
	info->last_hash_succ = FALSE;

	/* Currently, does not work if the following fails: */
	ut_a(!has_search_latch);
	
	btr_leaf_page_release(page, latch_mode, mtr);

	btr_cur_search_to_nth_level(index, 0, tuple, mode, latch_mode,
							&cursor2, 0, mtr);
	ut_a(btr_cur_get_rec(&cursor2) == btr_cur_get_rec(cursor));

	info->last_hash_succ = TRUE;
#endif

#ifdef UNIV_SEARCH_PERF_STAT
	btr_search_n_succ++;
#endif
	if (!has_search_latch && buf_block_peek_if_too_old(block)) {

		buf_page_make_young(page);
	}	

	return(TRUE);	

	/*-------------------------------------------*/
failure:
	info->n_hash_fail++;

	cursor->flag = BTR_CUR_HASH_FAIL;

#ifdef UNIV_SEARCH_PERF_STAT
	if (info->n_hash_succ > 0) {
		info->n_hash_succ--;
	}
#endif
	info->last_hash_succ = FALSE;

	return(FALSE);
}

/************************************************************************
Drops a page hash index. */

void
btr_search_drop_page_hash_index(
/*============================*/
	page_t*	page)	/* in: index page, s- or x-latched */
{
	hash_table_t*	table;
	buf_block_t*	block;
	ulint		n_fields;
	ulint		n_bytes;
	rec_t*		rec;
	rec_t*		sup;
	ulint		fold;
	ulint		prev_fold;
	dulint		tree_id;
	ulint		n_cached;
	ulint		n_recs;
	ulint*		folds;
	ulint		i;
	
	ut_ad(!rw_lock_own(&btr_search_latch, RW_LOCK_SHARED)
			&& !rw_lock_own(&btr_search_latch, RW_LOCK_EX));
		
	rw_lock_s_lock(&btr_search_latch);

	block = buf_block_align(page);

	if (!block->is_hashed) {

		rw_lock_s_unlock(&btr_search_latch);

		return;
	}

	table = btr_search_sys->hash_index;

	ut_ad(rw_lock_own(&(block->lock), RW_LOCK_SHARED)
	      			|| rw_lock_own(&(block->lock), RW_LOCK_EX)
	      			|| (block->buf_fix_count == 0));

	n_fields = block->curr_n_fields;
	n_bytes = block->curr_n_bytes;

	rw_lock_s_unlock(&btr_search_latch);
	
	n_recs = page_get_n_recs(page);

	/* Calculate and cache fold values into an array for fast deletion
	from the hash index */

	folds = mem_alloc(n_recs * sizeof(ulint));

	n_cached = 0;

	sup = page_get_supremum_rec(page);

	rec = page_get_infimum_rec(page);
	rec = page_rec_get_next(rec);

	tree_id = btr_page_get_index_id(page);
	
	prev_fold = 0;

	while (rec != sup) {
		/* FIXME: in a mixed tree, not all records may have enough
		ordering fields: */
		
		fold = rec_fold(rec, n_fields, n_bytes, tree_id);

		if ((fold == prev_fold) && (prev_fold != 0)) {

			goto next_rec;
		}

		/* Remove all hash nodes pointing to this page from the
		hash chain */

		folds[n_cached] = fold;
		n_cached++;
next_rec:
		rec = page_rec_get_next(rec);
	}

	rw_lock_x_lock(&btr_search_latch);

	for (i = 0; i < n_cached; i++) {

		ha_remove_all_nodes_to_page(table, folds[i], page);
	}

	block->is_hashed = FALSE;

	rw_lock_x_unlock(&btr_search_latch);

	mem_free(folds);
}

/************************************************************************
Drops a page hash index when a page is freed from a fseg to the file system.
Drops possible hash index if the page happens to be in the buffer pool. */

void
btr_search_drop_page_hash_when_freed(
/*=================================*/
	ulint	space,		/* in: space id */
	ulint	page_no)	/* in: page number */
{
	ibool	is_hashed;
	page_t*	page;
	mtr_t	mtr;

	is_hashed = buf_page_peek_if_search_hashed(space, page_no);

	if (!is_hashed) {

		return;
	}
	
	mtr_start(&mtr);

	/* We assume that if the caller has a latch on the page,
	then the caller has already drooped the hash index for the page,
	and we never get here. Therefore we can acquire the s-latch to
	the page without fearing a deadlock. */
	
	page = buf_page_get(space, page_no, RW_S_LATCH, &mtr);

	buf_page_dbg_add_level(page, SYNC_TREE_NODE_FROM_HASH);
	
	btr_search_drop_page_hash_index(page);

	mtr_commit(&mtr);
}

/************************************************************************
Builds a hash index on a page with the given parameters. If the page already
has a hash index with different parameters, the old hash index is removed. */
static
void
btr_search_build_page_hash_index(
/*=============================*/
	page_t*	page,		/* in: index page, s- or x-latched */
	ulint	n_fields,	/* in: hash this many full fields */
	ulint	n_bytes,	/* in: hash this many bytes from the next
				field */
	ulint	side)		/* in: hash for searches from this side */
{
	hash_table_t*	table;
	buf_block_t*	block;
	rec_t*		rec;
	rec_t*		next_rec;
	rec_t*		sup;
	ulint		fold;
	ulint		next_fold;
	dulint		tree_id;
	ulint		n_cached;
	ulint		n_recs;
	ulint*		folds;
	rec_t**		recs;
	ulint		i;
	
	block = buf_block_align(page);
	table = btr_search_sys->hash_index;

	ut_ad(!rw_lock_own(&btr_search_latch, RW_LOCK_EX));
	ut_ad(rw_lock_own(&(block->lock), RW_LOCK_SHARED)
				|| rw_lock_own(&(block->lock), RW_LOCK_EX));

	rw_lock_s_lock(&btr_search_latch);
				
	if (block->is_hashed && ((block->curr_n_fields != n_fields)
	        			|| (block->curr_n_bytes != n_bytes)
	        			|| (block->curr_side != side))) {

		rw_lock_s_unlock(&btr_search_latch);

		btr_search_drop_page_hash_index(page);
	} else {
		rw_lock_s_unlock(&btr_search_latch);
	}

	n_recs = page_get_n_recs(page);

	if (n_recs == 0) {

		return;
	}

	/* Calculate and cache fold values and corresponding records into
	an array for fast insertion to the hash index */

	folds = mem_alloc(n_recs * sizeof(ulint));
	recs = mem_alloc(n_recs * sizeof(rec_t*));

	n_cached = 0;

	tree_id = btr_page_get_index_id(page);

	sup = page_get_supremum_rec(page);

	rec = page_get_infimum_rec(page);
	rec = page_rec_get_next(rec);

	/* FIXME: in a mixed tree, all records may not have enough ordering
	fields: */
	
	fold = rec_fold(rec, n_fields, n_bytes, tree_id);

	if (side == BTR_SEARCH_LEFT_SIDE) {

		folds[n_cached] = fold;
		recs[n_cached] = rec;
		n_cached++;
	}
	
	for (;;) {
		next_rec = page_rec_get_next(rec);

		if (next_rec == sup) {

			if (side == BTR_SEARCH_RIGHT_SIDE) {
	
				folds[n_cached] = fold;
				recs[n_cached] = rec;
				n_cached++;
			}

		 	break;
		}

		next_fold = rec_fold(next_rec, n_fields, n_bytes, tree_id);

		if (fold != next_fold) {
			/* Insert an entry into the hash index */

			if (side == BTR_SEARCH_LEFT_SIDE) {

				folds[n_cached] = next_fold;
				recs[n_cached] = next_rec;
				n_cached++;
			} else {
				folds[n_cached] = fold;
				recs[n_cached] = rec;
				n_cached++;
			}
		}

		rec = next_rec;
		fold = next_fold;
	}

	btr_search_check_free_space_in_heap();

	rw_lock_x_lock(&btr_search_latch);

	if (block->is_hashed && ((block->curr_n_fields != n_fields)
	        			|| (block->curr_n_bytes != n_bytes)
	        			|| (block->curr_side != side))) {

		rw_lock_x_unlock(&btr_search_latch);

		mem_free(folds);
		mem_free(recs);

		return;
	}
	
	block->is_hashed = TRUE;
	block->n_hash_helps = 0;
	
	block->curr_n_fields = n_fields;
	block->curr_n_bytes = n_bytes;
	block->curr_side = side;

	for (i = 0; i < n_cached; i++) {
	
		ha_insert_for_fold(table, folds[i], recs[i]);
	}

	rw_lock_x_unlock(&btr_search_latch);

	mem_free(folds);
	mem_free(recs);
}

/************************************************************************
Moves or deletes hash entries for moved records. If new_page is already hashed,
then the hash index for page, if any, is dropped. If new_page is not hashed,
and page is hashed, then a new hash index is built to new_page with the same
parameters as page (this often happens when a page is split). */

void
btr_search_move_or_delete_hash_entries(
/*===================================*/
	page_t*	new_page,	/* in: records are copied to this page */
	page_t*	page)		/* in: index page from which records were
				copied, and the copied records will be deleted
				from this page */
{
	buf_block_t*	block;
	buf_block_t*	new_block;
	ulint		n_fields;
	ulint		n_bytes;
	ulint		side;

	block = buf_block_align(page);
	new_block = buf_block_align(new_page);

	ut_ad(rw_lock_own(&(block->lock), RW_LOCK_EX)
			&& rw_lock_own(&(new_block->lock), RW_LOCK_EX));

	rw_lock_s_lock(&btr_search_latch);
			
	if (new_block->is_hashed) {

		rw_lock_s_unlock(&btr_search_latch);

		btr_search_drop_page_hash_index(page);

		return;
	}

	if (block->is_hashed) {

		n_fields = block->curr_n_fields;
		n_bytes = block->curr_n_bytes;
		side = block->curr_side;

		new_block->n_fields = block->curr_n_fields;
		new_block->n_bytes = block->curr_n_bytes;
		new_block->side = block->curr_side;

		rw_lock_s_unlock(&btr_search_latch);

		btr_search_build_page_hash_index(new_page, n_fields, n_bytes,
									side);
		ut_a(n_fields == block->curr_n_fields);
		ut_a(n_bytes == block->curr_n_bytes);
		ut_a(side == block->curr_side);

		return;
	}

	rw_lock_s_unlock(&btr_search_latch);
}

/************************************************************************
Updates the page hash index when a single record is deleted from a page. */

void
btr_search_update_hash_on_delete(
/*=============================*/
	btr_cur_t*	cursor)	/* in: cursor which was positioned on the
				record to delete using btr_cur_search_...,
				the record is not yet deleted */
{
	hash_table_t*	table;
	buf_block_t*	block;
	rec_t*		rec;
	ulint		fold;
	dulint		tree_id;
	ibool		found;

	rec = btr_cur_get_rec(cursor);

	block = buf_block_align(rec);

	ut_ad(rw_lock_own(&(block->lock), RW_LOCK_EX));

	if (!block->is_hashed) {

		return;
	}

	table = btr_search_sys->hash_index;

	tree_id = ((cursor->index)->tree)->id;		

	fold = rec_fold(rec, block->curr_n_fields, block->curr_n_bytes,
								tree_id);
	rw_lock_x_lock(&btr_search_latch);

	found = ha_search_and_delete_if_found(table, fold, rec);

	rw_lock_x_unlock(&btr_search_latch);
}

/************************************************************************
Updates the page hash index when a single record is inserted on a page. */

void
btr_search_update_hash_node_on_insert(
/*==================================*/
	btr_cur_t*	cursor)	/* in: cursor which was positioned to the
				place to insert using btr_cur_search_...,
				and the new record has been inserted next
				to the cursor */
{
	hash_table_t*	table;
	buf_block_t*	block;
	rec_t*		rec;

	rec = btr_cur_get_rec(cursor);

	block = buf_block_align(rec);

	ut_ad(rw_lock_own(&(block->lock), RW_LOCK_EX));

	if (!block->is_hashed) {

		return;
	}

	rw_lock_x_lock(&btr_search_latch);

	if ((cursor->flag == BTR_CUR_HASH)
	    && (cursor->n_fields == block->curr_n_fields)
	    && (cursor->n_bytes == block->curr_n_bytes)
	    && (block->curr_side == BTR_SEARCH_RIGHT_SIDE)) {

	    	table = btr_search_sys->hash_index;
	    	
	    	ha_search_and_update_if_found(table, cursor->fold, rec,
						page_rec_get_next(rec));

		rw_lock_x_unlock(&btr_search_latch);
	} else {
		rw_lock_x_unlock(&btr_search_latch);

		btr_search_update_hash_on_insert(cursor);
	}
}

/************************************************************************
Updates the page hash index when a single record is inserted on a page. */

void
btr_search_update_hash_on_insert(
/*=============================*/
	btr_cur_t*	cursor)	/* in: cursor which was positioned to the
				place to insert using btr_cur_search_...,
				and the new record has been inserted next
				to the cursor */
{
	hash_table_t*	table; 
	buf_block_t*	block;
	page_t*		page;
	rec_t*		rec;
	rec_t*		ins_rec;
	rec_t*		next_rec;
	dulint		tree_id;
	ulint		fold;
	ulint		ins_fold;
	ulint		next_fold;
	ulint		n_fields;
	ulint		n_bytes;
	ulint		side;
	ibool		locked	= FALSE;

	table = btr_search_sys->hash_index;

	btr_search_check_free_space_in_heap();

	rec = btr_cur_get_rec(cursor);

	block = buf_block_align(rec);

	ut_ad(rw_lock_own(&(block->lock), RW_LOCK_EX));
	
	if (!block->is_hashed) {

		return;
	}

	tree_id = ((cursor->index)->tree)->id;

	n_fields = block->curr_n_fields;
	n_bytes = block->curr_n_bytes;
	side = block->curr_side;

	ins_rec = page_rec_get_next(rec);
	next_rec = page_rec_get_next(ins_rec);

	page = buf_frame_align(rec);

	ins_fold = rec_fold(ins_rec, n_fields, n_bytes, tree_id);

	if (next_rec != page_get_supremum_rec(page)) {
		next_fold = rec_fold(next_rec, n_fields, n_bytes, tree_id);
	}

	if (rec != page_get_infimum_rec(page)) {
		fold = rec_fold(rec, n_fields, n_bytes, tree_id);

	} else {
		if (side == BTR_SEARCH_LEFT_SIDE) {

			rw_lock_x_lock(&btr_search_latch);

			locked = TRUE;

			ha_insert_for_fold(table, ins_fold, ins_rec);
		}

		goto check_next_rec;
	}
	
 	if (fold != ins_fold) {

 		if (!locked) {

			rw_lock_x_lock(&btr_search_latch);

			locked = TRUE;
		}

		if (side == BTR_SEARCH_RIGHT_SIDE) {
			ha_insert_for_fold(table, fold, rec);
		} else {
			ha_insert_for_fold(table, ins_fold, ins_rec);
		}
	}

check_next_rec:
	if (next_rec == page_get_supremum_rec(page)) {

		if (side == BTR_SEARCH_RIGHT_SIDE) {

 			if (!locked) {
				rw_lock_x_lock(&btr_search_latch);

				locked = TRUE;
			}
			
			ha_insert_for_fold(table, ins_fold, ins_rec);
		}

		goto function_exit;
	}
	
	if (ins_fold != next_fold) {

 		if (!locked) {
	
			rw_lock_x_lock(&btr_search_latch);

			locked = TRUE;
		}

		if (side == BTR_SEARCH_RIGHT_SIDE) {

			ha_insert_for_fold(table, ins_fold, ins_rec);
/*
			printf("Hash insert for %s, fold %lu\n",
					cursor->index->name, ins_fold);
*/
		} else {
			ha_insert_for_fold(table, next_fold, next_rec);
		}
	}	
		
function_exit:
	if (locked) {
		rw_lock_x_unlock(&btr_search_latch);
	}
}

/************************************************************************
Prints info of the search system. */

void
btr_search_print_info(void)
/*=======================*/
{
	printf("SEARCH SYSTEM INFO\n");

	rw_lock_x_lock(&btr_search_latch);

	ha_print_info(btr_search_sys->hash_index);

	rw_lock_x_unlock(&btr_search_latch);
}

/************************************************************************
Prints info of searches on an index. */

void
btr_search_index_print_info(
/*========================*/
	dict_index_t*	index)	/* in: index */
{
	btr_search_t*	info;

	printf("INDEX SEARCH INFO\n");

	rw_lock_x_lock(&btr_search_latch);

	info = btr_search_get_info(index);

	printf("Searches %lu, hash succ %lu, fail %lu, patt succ %lu\n",
		info->n_searches, info->n_hash_succ, info->n_hash_fail,
		info->n_patt_succ);

	printf("Total of page cur short succ for all indexes %lu\n",
							page_cur_short_succ);
	rw_lock_x_unlock(&btr_search_latch);
}

/************************************************************************
Prints info of searches on a table. */

void
btr_search_table_print_info(
/*========================*/
	char*	name)	/* in: table name */
{
	dict_table_t*	table;
	dict_index_t*	index;

	mutex_enter(&(dict_sys->mutex));

	table = dict_table_get_low(name);

	ut_a(table);
	
	mutex_exit(&(dict_sys->mutex));

	index = dict_table_get_first_index(table);

	while (index) {
		btr_search_index_print_info(index);

		index = dict_table_get_next_index(index);
	}
}

/************************************************************************
Validates the search system. */

ibool
btr_search_validate(void)
/*=====================*/
				/* out: TRUE if ok */
{
	rw_lock_x_lock(&btr_search_latch);
	
	ut_a(ha_validate(btr_search_sys->hash_index));

	rw_lock_x_unlock(&btr_search_latch);

	return(TRUE);
}