/***************************************************************************** Copyright (c) 1995, 2016, Oracle and/or its affiliates. All Rights Reserved. Copyright (c) 2017, 2022, 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 include/buf0lru.h The database buffer pool LRU replacement algorithm Created 11/5/1995 Heikki Tuuri *******************************************************/ #pragma once #include "buf0types.h" #include "hash0hash.h" // Forward declaration struct trx_t; struct fil_space_t; /** Flush this many pages in buf_LRU_get_free_block() */ extern size_t innodb_lru_flush_size; /*####################################################################### These are low-level functions #########################################################################*/ /** Minimum LRU list length for which the LRU_old pointer is defined */ #define BUF_LRU_OLD_MIN_LEN 512 /* 8 megabytes of 16k pages */ /** Try to free a block. If bpage is a descriptor of a compressed-only ROW_FORMAT=COMPRESSED page, the buf_page_t object will be freed as well. The caller must hold buf_pool.mutex. @param bpage block to be freed @param zip whether to remove both copies of a ROW_FORMAT=COMPRESSED page @retval true if freed and buf_pool.mutex may have been temporarily released @retval false if the page was not freed */ bool buf_LRU_free_page(buf_page_t *bpage, bool zip) MY_ATTRIBUTE((nonnull)); /** Try to free a replaceable block. @param limit maximum number of blocks to scan @return true if found and freed */ bool buf_LRU_scan_and_free_block(ulint limit= ULINT_UNDEFINED); /** @return a buffer block from the buf_pool.free list @retval NULL if the free list is empty */ buf_block_t* buf_LRU_get_free_only(); /** How to acquire a block */ enum buf_LRU_get { /** The caller is not holding buf_pool.mutex */ have_no_mutex= 0, /** The caller is holding buf_pool.mutex */ have_mutex, /** The caller is not holding buf_pool.mutex and is OK if a block cannot be allocated. */ have_no_mutex_soft }; /** Get a block from the buf_pool.free list. If the list is empty, blocks will be moved from the end of buf_pool.LRU to buf_pool.free. This function is called from a user thread when it needs a clean block to read in a page. Note that we only ever get a block from the free list. Even when we flush a page or find a page in LRU scan we put it to free list to be used. * iteration 0: * get a block from the buf_pool.free list, success:done * if buf_pool.try_LRU_scan is set * scan LRU up to 100 pages to free a clean block * success:retry the free list * flush up to innodb_lru_flush_size LRU blocks to data files (until UT_LIST_GET_GEN(buf_pool.free) < innodb_lru_scan_depth) * on buf_page_write_complete() the blocks will put on buf_pool.free list * success: retry the free list * subsequent iterations: same as iteration 0 except: * scan whole LRU list * scan LRU list even if buf_pool.try_LRU_scan is not set @param get how to allocate the block @return the free control block, in state BUF_BLOCK_MEMORY @retval nullptr if get==have_no_mutex_soft and memory was not available */ buf_block_t* buf_LRU_get_free_block(buf_LRU_get get) MY_ATTRIBUTE((malloc,warn_unused_result)); /** @return whether the unzip_LRU list should be used for evicting a victim instead of the general LRU list */ bool buf_LRU_evict_from_unzip_LRU(); /** Puts a block back to the free list. @param[in] block block; not containing a file page */ void buf_LRU_block_free_non_file_page(buf_block_t* block); /******************************************************************//** Adds a block to the LRU list. Please make sure that the page_size is already set when invoking the function, so that we can get correct page_size from the buffer page when adding a block into LRU */ void buf_LRU_add_block( /*==============*/ buf_page_t* bpage, /*!< in: control block */ bool old); /*!< in: true if should be put to the old blocks in the LRU list, else put to the start; if the LRU list is very short, added to the start regardless of this parameter */ /** Move a block to the start of the buf_pool.LRU list. @param bpage buffer pool page */ void buf_page_make_young(buf_page_t *bpage); /** Flag a page accessed in buf_pool and move it to the start of buf_pool.LRU if it is too old. @param bpage buffer pool page @return whether this is not the first access */ bool buf_page_make_young_if_needed(buf_page_t *bpage); /******************************************************************//** Adds a block to the LRU list of decompressed zip pages. */ void buf_unzip_LRU_add_block( /*====================*/ buf_block_t* block, /*!< in: control block */ ibool old); /*!< in: TRUE if should be put to the end of the list, else put to the start */ /** Evict the temporary tablespace pages above the given threshold @param threshold Above this page to be removed from LRU list */ void buf_LRU_truncate_temp(uint32_t threshold); /** Update buf_pool.LRU_old_ratio. @param[in] old_pct Reserve this percentage of the buffer pool for "old" blocks @param[in] adjust true=adjust the LRU list; false=just assign buf_pool.LRU_old_ratio during the initialization of InnoDB @return updated old_pct */ uint buf_LRU_old_ratio_update(uint old_pct, bool adjust); /********************************************************************//** Update the historical stats that we are collecting for LRU eviction policy at the end of each interval. */ void buf_LRU_stat_update(); #ifdef UNIV_DEBUG /** Validate the LRU list. */ void buf_LRU_validate(); #endif /* UNIV_DEBUG */ #if defined UNIV_DEBUG_PRINT || defined UNIV_DEBUG /** Dump the LRU list to stderr. */ void buf_LRU_print(); #endif /* UNIV_DEBUG_PRINT || UNIV_DEBUG */ /** @name Heuristics for detecting index scan @{ */ /** The denominator of buf_pool.LRU_old_ratio. */ #define BUF_LRU_OLD_RATIO_DIV 1024 /** Maximum value of buf_pool.LRU_old_ratio. @see buf_LRU_old_adjust_len @see buf_pool.LRU_old_ratio_update */ #define BUF_LRU_OLD_RATIO_MAX BUF_LRU_OLD_RATIO_DIV /** Minimum value of buf_pool.LRU_old_ratio. @see buf_LRU_old_adjust_len @see buf_pool.LRU_old_ratio_update The minimum must exceed (BUF_LRU_OLD_TOLERANCE + 5) * BUF_LRU_OLD_RATIO_DIV / BUF_LRU_OLD_MIN_LEN. */ #define BUF_LRU_OLD_RATIO_MIN 51 #if BUF_LRU_OLD_RATIO_MIN >= BUF_LRU_OLD_RATIO_MAX # error "BUF_LRU_OLD_RATIO_MIN >= BUF_LRU_OLD_RATIO_MAX" #endif #if BUF_LRU_OLD_RATIO_MAX > BUF_LRU_OLD_RATIO_DIV # error "BUF_LRU_OLD_RATIO_MAX > BUF_LRU_OLD_RATIO_DIV" #endif /** Move blocks to "new" LRU list only if the first access was at least this many milliseconds ago. Not protected by any mutex or latch. */ extern uint buf_LRU_old_threshold_ms; /* @} */ /** @brief Statistics for selecting the LRU list for eviction. These statistics are not 'of' LRU but 'for' LRU. We keep count of I/O and page_zip_decompress() operations. Based on the statistics we decide if we want to evict from buf_pool.unzip_LRU or buf_pool.LRU. */ struct buf_LRU_stat_t { ulint io; /**< Counter of buffer pool I/O operations. */ ulint unzip; /**< Counter of page_zip_decompress operations. */ }; /** Current operation counters. Not protected by any mutex. Cleared by buf_LRU_stat_update(). */ extern buf_LRU_stat_t buf_LRU_stat_cur; /** Running sum of past values of buf_LRU_stat_cur. Updated by buf_LRU_stat_update(). Protected by buf_pool.mutex. */ extern buf_LRU_stat_t buf_LRU_stat_sum; /********************************************************************//** Increments the I/O counter in buf_LRU_stat_cur. */ #define buf_LRU_stat_inc_io() buf_LRU_stat_cur.io++ /********************************************************************//** Increments the page_zip_decompress() counter in buf_LRU_stat_cur. */ #define buf_LRU_stat_inc_unzip() buf_LRU_stat_cur.unzip++