/* Copyright (C) 2001 MySQL AB 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ /* Function to handle quick removal of duplicates This code is used when doing multi-table deletes to find the rows in reference tables that needs to be deleted. The basic idea is as follows: Store first all strings in a binary tree, ignoring duplicates. When the tree uses more memory than 'max_heap_table_size', write the tree (in sorted order) out to disk and start with a new tree. When all data has been generated, merge the trees (removing any found duplicates). The unique entries will be returned in sort order, to ensure that we do the deletes in disk order. */ #include "sql_priv.h" #include "unireg.h" #include "sql_sort.h" #include "queues.h" // QUEUE #include "my_tree.h" // element_count #include "sql_class.h" // Unique int unique_write_to_file(uchar* key, element_count count, Unique *unique) { /* Use unique->size (size of element stored in the tree) and not unique->tree.size_of_element. The latter is different from unique->size when tree implementation chooses to store pointer to key in TREE_ELEMENT (instead of storing the element itself there) */ return my_b_write(&unique->file, key, unique->size) ? 1 : 0; } int unique_write_to_ptrs(uchar* key, element_count count, Unique *unique) { memcpy(unique->record_pointers, key, unique->size); unique->record_pointers+=unique->size; return 0; } Unique::Unique(qsort_cmp2 comp_func, void * comp_func_fixed_arg, uint size_arg, ulonglong max_in_memory_size_arg) :max_in_memory_size(max_in_memory_size_arg), size(size_arg), elements(0) { my_b_clear(&file); init_tree(&tree, (ulong) (max_in_memory_size / 16), 0, size, comp_func, 0, NULL, comp_func_fixed_arg); /* If the following fail's the next add will also fail */ my_init_dynamic_array(&file_ptrs, sizeof(BUFFPEK), 16, 16); /* If you change the following, change it in get_max_elements function, too. */ max_elements= (ulong) (max_in_memory_size / ALIGN_SIZE(sizeof(TREE_ELEMENT)+size)); (void) open_cached_file(&file, mysql_tmpdir,TEMP_PREFIX, DISK_BUFFER_SIZE, MYF(MY_WME)); } /* Calculate log2(n!) NOTES Stirling's approximate formula is used: n! ~= sqrt(2*M_PI*n) * (n/M_E)^n Derivation of formula used for calculations is as follows: log2(n!) = log(n!)/log(2) = log(sqrt(2*M_PI*n)*(n/M_E)^n) / log(2) = = (log(2*M_PI*n)/2 + n*log(n/M_E)) / log(2). */ inline double log2_n_fact(double x) { return (log(2*M_PI*x)/2 + x*log(x/M_E)) / M_LN2; } /* Calculate cost of merge_buffers function call for given sequence of input stream lengths and store the number of rows in result stream in *last. SYNOPSIS get_merge_buffers_cost() buff_elems Array of #s of elements in buffers elem_size Size of element stored in buffer first Pointer to first merged element size last Pointer to last merged element size RETURN Cost of merge_buffers operation in disk seeks. NOTES It is assumed that no rows are eliminated during merge. The cost is calculated as cost(read_and_write) + cost(merge_comparisons). All bytes in the sequences is read and written back during merge so cost of disk io is 2*elem_size*total_buf_elems/IO_SIZE (2 is for read + write) For comparisons cost calculations we assume that all merged sequences have the same length, so each of total_buf_size elements will be added to a sort heap with (n_buffers-1) elements. This gives the comparison cost: total_buf_elems* log2(n_buffers) / TIME_FOR_COMPARE_ROWID; */ static double get_merge_buffers_cost(uint *buff_elems, uint elem_size, uint *first, uint *last) { uint total_buf_elems= 0; for (uint *pbuf= first; pbuf <= last; pbuf++) total_buf_elems+= *pbuf; *last= total_buf_elems; size_t n_buffers= last - first + 1; /* Using log2(n)=log(n)/log(2) formula */ return 2*((double)total_buf_elems*elem_size) / IO_SIZE + total_buf_elems*log((double) n_buffers) / (TIME_FOR_COMPARE_ROWID * M_LN2); } /* Calculate cost of merging buffers into one in Unique::get, i.e. calculate how long (in terms of disk seeks) the two calls merge_many_buffs(...); merge_buffers(...); will take. SYNOPSIS get_merge_many_buffs_cost() buffer buffer space for temporary data, at least Unique::get_cost_calc_buff_size bytes maxbuffer # of full buffers max_n_elems # of elements in first maxbuffer buffers last_n_elems # of elements in last buffer elem_size size of buffer element NOTES maxbuffer+1 buffers are merged, where first maxbuffer buffers contain max_n_elems elements each and last buffer contains last_n_elems elements. The current implementation does a dumb simulation of merge_many_buffs function actions. RETURN Cost of merge in disk seeks. */ static double get_merge_many_buffs_cost(uint *buffer, uint maxbuffer, uint max_n_elems, uint last_n_elems, int elem_size) { register int i; double total_cost= 0.0; uint *buff_elems= buffer; /* #s of elements in each of merged sequences */ /* Set initial state: first maxbuffer sequences contain max_n_elems elements each, last sequence contains last_n_elems elements. */ for (i = 0; i < (int)maxbuffer; i++) buff_elems[i]= max_n_elems; buff_elems[maxbuffer]= last_n_elems; /* Do it exactly as merge_many_buff function does, calling get_merge_buffers_cost to get cost of merge_buffers. */ if (maxbuffer >= MERGEBUFF2) { while (maxbuffer >= MERGEBUFF2) { uint lastbuff= 0; for (i = 0; i <= (int) maxbuffer - MERGEBUFF*3/2; i += MERGEBUFF) { total_cost+=get_merge_buffers_cost(buff_elems, elem_size, buff_elems + i, buff_elems + i + MERGEBUFF-1); lastbuff++; } total_cost+=get_merge_buffers_cost(buff_elems, elem_size, buff_elems + i, buff_elems + maxbuffer); maxbuffer= lastbuff; } } /* Simulate final merge_buff call. */ total_cost += get_merge_buffers_cost(buff_elems, elem_size, buff_elems, buff_elems + maxbuffer); return total_cost; } /* Calculate cost of using Unique for processing nkeys elements of size key_size using max_in_memory_size memory. SYNOPSIS Unique::get_use_cost() buffer space for temporary data, use Unique::get_cost_calc_buff_size to get # bytes needed. nkeys #of elements in Unique key_size size of each elements in bytes max_in_memory_size amount of memory Unique will be allowed to use RETURN Cost in disk seeks. NOTES cost(using_unqiue) = cost(create_trees) + (see #1) cost(merge) + (see #2) cost(read_result) (see #3) 1. Cost of trees creation For each Unique::put operation there will be 2*log2(n+1) elements comparisons, where n runs from 1 tree_size (we assume that all added elements are different). Together this gives: n_compares = 2*(log2(2) + log2(3) + ... + log2(N+1)) = 2*log2((N+1)!) then cost(tree_creation) = n_compares*ROWID_COMPARE_COST; Total cost of creating trees: (n_trees - 1)*max_size_tree_cost + non_max_size_tree_cost. Approximate value of log2(N!) is calculated by log2_n_fact function. 2. Cost of merging. If only one tree is created by Unique no merging will be necessary. Otherwise, we model execution of merge_many_buff function and count #of merges. (The reason behind this is that number of buffers is small, while size of buffers is big and we don't want to loose precision with O(x)-style formula) 3. If only one tree is created by Unique no disk io will happen. Otherwise, ceil(key_len*n_keys) disk seeks are necessary. We assume these will be random seeks. */ double Unique::get_use_cost(uint *buffer, uint nkeys, uint key_size, ulonglong max_in_memory_size) { ulong max_elements_in_tree; ulong last_tree_elems; int n_full_trees; /* number of trees in unique - 1 */ double result; max_elements_in_tree= ((ulong) max_in_memory_size / ALIGN_SIZE(sizeof(TREE_ELEMENT)+key_size)); n_full_trees= nkeys / max_elements_in_tree; last_tree_elems= nkeys % max_elements_in_tree; /* Calculate cost of creating trees */ result= 2*log2_n_fact(last_tree_elems + 1.0); if (n_full_trees) result+= n_full_trees * log2_n_fact(max_elements_in_tree + 1.0); result /= TIME_FOR_COMPARE_ROWID; DBUG_PRINT("info",("unique trees sizes: %u=%u*%lu + %lu", nkeys, n_full_trees, n_full_trees?max_elements_in_tree:0, last_tree_elems)); if (!n_full_trees) return result; /* There is more then one tree and merging is necessary. First, add cost of writing all trees to disk, assuming that all disk writes are sequential. */ result += DISK_SEEK_BASE_COST * n_full_trees * ceil(((double) key_size)*max_elements_in_tree / IO_SIZE); result += DISK_SEEK_BASE_COST * ceil(((double) key_size)*last_tree_elems / IO_SIZE); /* Cost of merge */ double merge_cost= get_merge_many_buffs_cost(buffer, n_full_trees, max_elements_in_tree, last_tree_elems, key_size); if (merge_cost < 0.0) return merge_cost; result += merge_cost; /* Add cost of reading the resulting sequence, assuming there were no duplicate elements. */ result += ceil((double)key_size*nkeys/IO_SIZE); return result; } Unique::~Unique() { close_cached_file(&file); delete_tree(&tree); delete_dynamic(&file_ptrs); } /* Write tree to disk; clear tree */ bool Unique::flush() { BUFFPEK file_ptr; elements+= tree.elements_in_tree; file_ptr.count=tree.elements_in_tree; file_ptr.file_pos=my_b_tell(&file); if (tree_walk(&tree, (tree_walk_action) unique_write_to_file, (void*) this, left_root_right) || insert_dynamic(&file_ptrs, (uchar*) &file_ptr)) return 1; delete_tree(&tree); return 0; } /* Clear the tree and the file. You must call reset() if you want to reuse Unique after walk(). */ void Unique::reset() { reset_tree(&tree); /* If elements != 0, some trees were stored in the file (see how flush() works). Note, that we can not count on my_b_tell(&file) == 0 here, because it can return 0 right after walk(), and walk() does not reset any Unique member. */ if (elements) { reset_dynamic(&file_ptrs); reinit_io_cache(&file, WRITE_CACHE, 0L, 0, 1); } elements= 0; } /* The comparison function, passed to queue_init() in merge_walk() and in merge_buffers() when the latter is called from Uniques::get() must use comparison function of Uniques::tree, but compare members of struct BUFFPEK. */ C_MODE_START static int buffpek_compare(void *arg, uchar *key_ptr1, uchar *key_ptr2) { BUFFPEK_COMPARE_CONTEXT *ctx= (BUFFPEK_COMPARE_CONTEXT *) arg; return ctx->key_compare(ctx->key_compare_arg, *((uchar **) key_ptr1), *((uchar **)key_ptr2)); } C_MODE_END /* DESCRIPTION Function is very similar to merge_buffers, but instead of writing sorted unique keys to the output file, it invokes walk_action for each key. This saves I/O if you need to pass through all unique keys only once. SYNOPSIS merge_walk() All params are 'IN' (but see comment for begin, end): merge_buffer buffer to perform cached piece-by-piece loading of trees; initially the buffer is empty merge_buffer_size size of merge_buffer. Must be aligned with key_length key_length size of tree element; key_length * (end - begin) must be less or equal than merge_buffer_size. begin pointer to BUFFPEK struct for the first tree. end pointer to BUFFPEK struct for the last tree; end > begin and [begin, end) form a consecutive range. BUFFPEKs structs in that range are used and overwritten in merge_walk(). walk_action element visitor. Action is called for each unique key. walk_action_arg argument to walk action. Passed to it on each call. compare elements comparison function compare_arg comparison function argument file file with all trees dumped. Trees in the file must contain sorted unique values. Cache must be initialized in read mode. RETURN VALUE 0 ok <> 0 error */ static bool merge_walk(uchar *merge_buffer, ulong merge_buffer_size, uint key_length, BUFFPEK *begin, BUFFPEK *end, tree_walk_action walk_action, void *walk_action_arg, qsort_cmp2 compare, void *compare_arg, IO_CACHE *file) { BUFFPEK_COMPARE_CONTEXT compare_context = { compare, compare_arg }; QUEUE queue; if (end <= begin || merge_buffer_size < (ulong) (key_length * (end - begin + 1)) || init_queue(&queue, (uint) (end - begin), offsetof(BUFFPEK, key), 0, buffpek_compare, &compare_context)) return 1; /* we need space for one key when a piece of merge buffer is re-read */ merge_buffer_size-= key_length; uchar *save_key_buff= merge_buffer + merge_buffer_size; uint max_key_count_per_piece= (uint) (merge_buffer_size/(end-begin) / key_length); /* if piece_size is aligned reuse_freed_buffer will always hit */ uint piece_size= max_key_count_per_piece * key_length; uint bytes_read; /* to hold return value of read_to_buffer */ BUFFPEK *top; int res= 1; /* Invariant: queue must contain top element from each tree, until a tree is not completely walked through. Here we're forcing the invariant, inserting one element from each tree to the queue. */ for (top= begin; top != end; ++top) { top->base= merge_buffer + (top - begin) * piece_size; top->max_keys= max_key_count_per_piece; bytes_read= read_to_buffer(file, top, key_length); if (bytes_read == (uint) (-1)) goto end; DBUG_ASSERT(bytes_read); queue_insert(&queue, (uchar *) top); } top= (BUFFPEK *) queue_top(&queue); while (queue.elements > 1) { /* Every iteration one element is removed from the queue, and one is inserted by the rules of the invariant. If two adjacent elements on the top of the queue are not equal, biggest one is unique, because all elements in each tree are unique. Action is applied only to unique elements. */ void *old_key= top->key; /* read next key from the cache or from the file and push it to the queue; this gives new top. */ top->key+= key_length; if (--top->mem_count) queue_replaced(&queue); else /* next piece should be read */ { /* save old_key not to overwrite it in read_to_buffer */ memcpy(save_key_buff, old_key, key_length); old_key= save_key_buff; bytes_read= read_to_buffer(file, top, key_length); if (bytes_read == (uint) (-1)) goto end; else if (bytes_read > 0) /* top->key, top->mem_count are reset */ queue_replaced(&queue); /* in read_to_buffer */ else { /* Tree for old 'top' element is empty: remove it from the queue and give all its memory to the nearest tree. */ queue_remove(&queue, 0); reuse_freed_buff(&queue, top, key_length); } } top= (BUFFPEK *) queue_top(&queue); /* new top has been obtained; if old top is unique, apply the action */ if (compare(compare_arg, old_key, top->key)) { if (walk_action(old_key, 1, walk_action_arg)) goto end; } } /* Applying walk_action to the tail of the last tree: this is safe because either we had only one tree in the beginning, either we work with the last tree in the queue. */ do { do { if (walk_action(top->key, 1, walk_action_arg)) goto end; top->key+= key_length; } while (--top->mem_count); bytes_read= read_to_buffer(file, top, key_length); if (bytes_read == (uint) (-1)) goto end; } while (bytes_read); res= 0; end: delete_queue(&queue); return res; } /* DESCRIPTION Walks consecutively through all unique elements: if all elements are in memory, then it simply invokes 'tree_walk', else all flushed trees are loaded to memory piece-by-piece, pieces are sorted, and action is called for each unique value. Note: so as merging resets file_ptrs state, this method can change internal Unique state to undefined: if you want to reuse Unique after walk() you must call reset() first! SYNOPSIS Unique:walk() All params are 'IN': action function-visitor, typed in include/my_tree.h function is called for each unique element arg argument for visitor, which is passed to it on each call RETURN VALUE 0 OK <> 0 error */ bool Unique::walk(tree_walk_action action, void *walk_action_arg) { int res; uchar *merge_buffer; if (elements == 0) /* the whole tree is in memory */ return tree_walk(&tree, action, walk_action_arg, left_root_right); /* flush current tree to the file to have some memory for merge buffer */ if (flush()) return 1; if (flush_io_cache(&file) || reinit_io_cache(&file, READ_CACHE, 0L, 0, 0)) return 1; if (!(merge_buffer= (uchar *) my_malloc((ulong) max_in_memory_size, MYF(0)))) return 1; res= merge_walk(merge_buffer, (ulong) max_in_memory_size, size, (BUFFPEK *) file_ptrs.buffer, (BUFFPEK *) file_ptrs.buffer + file_ptrs.elements, action, walk_action_arg, tree.compare, tree.custom_arg, &file); my_free(merge_buffer); return res; } /* Modify the TABLE element so that when one calls init_records() the rows will be read in priority order. */ bool Unique::get(TABLE *table) { SORTPARAM sort_param; table->sort.found_records=elements+tree.elements_in_tree; if (my_b_tell(&file) == 0) { /* Whole tree is in memory; Don't use disk if you don't need to */ if ((record_pointers=table->sort.record_pointers= (uchar*) my_malloc(size * tree.elements_in_tree, MYF(0)))) { (void) tree_walk(&tree, (tree_walk_action) unique_write_to_ptrs, this, left_root_right); return 0; } } /* Not enough memory; Save the result to file && free memory used by tree */ if (flush()) return 1; IO_CACHE *outfile=table->sort.io_cache; BUFFPEK *file_ptr= (BUFFPEK*) file_ptrs.buffer; uint maxbuffer= file_ptrs.elements - 1; uchar *sort_buffer; my_off_t save_pos; bool error=1; /* Open cached file if it isn't open */ outfile=table->sort.io_cache=(IO_CACHE*) my_malloc(sizeof(IO_CACHE), MYF(MY_ZEROFILL)); if (!outfile || (! my_b_inited(outfile) && open_cached_file(outfile,mysql_tmpdir,TEMP_PREFIX,READ_RECORD_BUFFER, MYF(MY_WME)))) return 1; reinit_io_cache(outfile,WRITE_CACHE,0L,0,0); bzero((char*) &sort_param,sizeof(sort_param)); sort_param.max_rows= elements; sort_param.sort_form=table; sort_param.rec_length= sort_param.sort_length= sort_param.ref_length= size; sort_param.keys= (uint) (max_in_memory_size / sort_param.sort_length); sort_param.not_killable=1; if (!(sort_buffer=(uchar*) my_malloc((sort_param.keys+1) * sort_param.sort_length, MYF(0)))) return 1; sort_param.unique_buff= sort_buffer+(sort_param.keys* sort_param.sort_length); sort_param.compare= (qsort2_cmp) buffpek_compare; sort_param.cmp_context.key_compare= tree.compare; sort_param.cmp_context.key_compare_arg= tree.custom_arg; /* Merge the buffers to one file, removing duplicates */ if (merge_many_buff(&sort_param,sort_buffer,file_ptr,&maxbuffer,&file)) goto err; if (flush_io_cache(&file) || reinit_io_cache(&file,READ_CACHE,0L,0,0)) goto err; if (merge_buffers(&sort_param, &file, outfile, sort_buffer, file_ptr, file_ptr, file_ptr+maxbuffer,0)) goto err; error=0; err: my_free(sort_buffer); if (flush_io_cache(outfile)) error=1; /* Setup io_cache for reading */ save_pos=outfile->pos_in_file; if (reinit_io_cache(outfile,READ_CACHE,0L,0,0)) error=1; outfile->end_of_file=save_pos; return error; }