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Diffstat (limited to 'sql/filesort_utils.h')
| -rw-r--r-- | sql/filesort_utils.h | 275 |
1 files changed, 275 insertions, 0 deletions
diff --git a/sql/filesort_utils.h b/sql/filesort_utils.h new file mode 100644 index 00000000..946b1cb4 --- /dev/null +++ b/sql/filesort_utils.h @@ -0,0 +1,275 @@ +/* Copyright (c) 2010, 2012 Oracle and/or its affiliates. All rights reserved. + + 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 St, Fifth Floor, Boston, MA 02110-1335 USA */ + +#ifndef FILESORT_UTILS_INCLUDED +#define FILESORT_UTILS_INCLUDED + +#include "my_base.h" +#include "sql_array.h" + +class Sort_param; +/* + Calculate cost of merge sort + + @param num_rows Total number of rows. + @param num_keys_per_buffer Number of keys per buffer. + @param elem_size Size of each element. + + Calculates cost of merge sort by simulating call to merge_many_buff(). + + @retval + Computed cost of merge sort in disk seeks. + + @note + Declared here in order to be able to unit test it, + since library dependencies have not been sorted out yet. + + See also comments get_merge_many_buffs_cost(). +*/ + +double get_merge_many_buffs_cost_fast(ha_rows num_rows, + ha_rows num_keys_per_buffer, + uint elem_size); + + +/** + A wrapper class around the buffer used by filesort(). + The sort buffer is a contiguous chunk of memory, + containing both records to be sorted, and pointers to said records: + + <start of buffer | still unused | end of buffer> + |rec 0|record 1 |rec 2| ............ |ptr to rec2|ptr to rec1|ptr to rec0| + + Records will be inserted "left-to-right". Records are not necessarily + fixed-size, they can be packed and stored without any "gaps". + + Record pointers will be inserted "right-to-left", as a side-effect + of inserting the actual records. + + We wrap the buffer in order to be able to do lazy initialization of the + pointers: the buffer is often much larger than what we actually need. + + With this allocation scheme, and lazy initialization of the pointers, + we are able to pack variable-sized records in the buffer, + and thus possibly have space for more records than we initially estimated. + + The buffer must be kept available for multiple executions of the + same sort operation, so we have explicit allocate and free functions, + rather than doing alloc/free in CTOR/DTOR. +*/ + +class Filesort_buffer +{ +public: + Filesort_buffer() : + m_next_rec_ptr(NULL), m_rawmem(NULL), m_record_pointers(NULL), + m_sort_keys(NULL), + m_num_records(0), m_record_length(0), + m_sort_length(0), + m_size_in_bytes(0), m_idx(0) + {} + + /** Sort me... */ + void sort_buffer(const Sort_param *param, uint count); + + /** + Reverses the record pointer array, to avoid recording new results for + non-deterministic mtr tests. + */ + void reverse_record_pointers() + { + if (m_idx < 2) // There is nothing to swap. + return; + uchar **keys= get_sort_keys(); + const longlong count= m_idx - 1; + for (longlong ix= 0; ix <= count/2; ++ix) + { + uchar *tmp= keys[count - ix]; + keys[count - ix] = keys[ix]; + keys[ix]= tmp; + } + } + + /** + Initializes all the record pointers. + */ + void init_record_pointers() + { + init_next_record_pointer(); + while (m_idx < m_num_records) + (void) get_next_record_pointer(); + reverse_record_pointers(); + } + + /** + Prepares the buffer for the next batch of records to process. + */ + void init_next_record_pointer() + { + m_idx= 0; + m_next_rec_ptr= m_rawmem; + m_sort_keys= NULL; + } + + /** + @returns the number of bytes currently in use for data. + */ + size_t space_used_for_data() const + { + return m_next_rec_ptr ? m_next_rec_ptr - m_rawmem : 0; + } + + /** + @returns the number of bytes left in the buffer. + */ + size_t spaceleft() const + { + DBUG_ASSERT(m_next_rec_ptr >= m_rawmem); + const size_t spaceused= + (m_next_rec_ptr - m_rawmem) + + (static_cast<size_t>(m_idx) * sizeof(uchar*)); + return m_size_in_bytes - spaceused; + } + + /** + Is the buffer full? + */ + bool isfull() const + { + if (m_idx < m_num_records) + return false; + return spaceleft() < (m_record_length + sizeof(uchar*)); + } + + /** + Where should the next record be stored? + */ + uchar *get_next_record_pointer() + { + uchar *retval= m_next_rec_ptr; + // Save the return value in the record pointer array. + m_record_pointers[-m_idx]= m_next_rec_ptr; + // Prepare for the subsequent request. + m_idx++; + m_next_rec_ptr+= m_record_length; + return retval; + } + + /** + Adjusts for actual record length. get_next_record_pointer() above was + pessimistic, and assumed that the record could not be packed. + */ + void adjust_next_record_pointer(uint val) + { + m_next_rec_ptr-= (m_record_length - val); + } + + /// Returns total size: pointer array + record buffers. + size_t sort_buffer_size() const + { + return m_size_in_bytes; + } + + bool is_allocated() const + { + return m_rawmem; + } + + /** + Allocates the buffer, but does *not* initialize pointers. + Total size = (num_records * record_length) + (num_records * sizeof(pointer)) + space for records space for pointer to records + Caller is responsible for raising an error if allocation fails. + + @param num_records Number of records. + @param record_length (maximum) size of each record. + @returns Pointer to allocated area, or NULL in case of out-of-memory. + */ + uchar *alloc_sort_buffer(uint num_records, uint record_length); + + /// Frees the buffer. + void free_sort_buffer(); + + void reset() + { + m_rawmem= NULL; + } + /** + Used to access the "right-to-left" array of record pointers as an ordinary + "left-to-right" array, so that we can pass it directly on to std::sort(). + */ + uchar **get_sort_keys() + { + if (m_idx == 0) + return NULL; + return &m_record_pointers[1 - m_idx]; + } + + /** + Gets sorted record number ix. @see get_sort_keys() + Only valid after buffer has been sorted! + */ + uchar *get_sorted_record(uint ix) + { + return m_sort_keys[ix]; + } + + /** + @returns The entire buffer, as a character array. + This is for reusing the memory for merge buffers. + */ + Bounds_checked_array<uchar> get_raw_buf() + { + return Bounds_checked_array<uchar>(m_rawmem, m_size_in_bytes); + } + + /** + We need an assignment operator, see filesort(). + This happens to have the same semantics as the one that would be + generated by the compiler. + Note that this is a shallow copy. We have two objects sharing the same + array. + */ + Filesort_buffer &operator=(const Filesort_buffer &rhs) = default; + + uint get_sort_length() const { return m_sort_length; } + void set_sort_length(uint val) { m_sort_length= val; } + +private: + uchar *m_next_rec_ptr; /// The next record will be inserted here. + uchar *m_rawmem; /// The raw memory buffer. + uchar **m_record_pointers; /// The "right-to-left" array of record pointers. + uchar **m_sort_keys; /// Caches the value of get_sort_keys() + uint m_num_records; /// Saved value from alloc_sort_buffer() + uint m_record_length; /// Saved value from alloc_sort_buffer() + uint m_sort_length; /// The length of the sort key. + size_t m_size_in_bytes; /// Size of raw buffer, in bytes. + + /** + This is the index in the "right-to-left" array of the next record to + be inserted into the buffer. It is signed, because we use it in signed + expressions like: + m_record_pointers[-m_idx]; + It is longlong rather than int, to ensure that it covers UINT_MAX32 + without any casting/warning. + */ + longlong m_idx; +}; + +int compare_packed_sort_keys(void *sort_keys, unsigned char **a, + unsigned char **b); +qsort2_cmp get_packed_keys_compare_ptr(); + +#endif // FILESORT_UTILS_INCLUDED |