buf0lru.h

Go to the documentation of this file.

/*****************************************************************************
 
Copyright (c) 1995, 2023, Oracle and/or its affiliates.
 
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License, version 2.0, as published by the
Free Software Foundation.
 
This program is also distributed with certain software (including but not
limited to OpenSSL) that is licensed under separate terms, as designated in a
particular file or component or in included license documentation. The authors
of MySQL hereby grant you an additional permission to link the program and
your derivative works with the separately licensed software that they have
included with MySQL.
 
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, version 2.0,
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 02110-1301  USA
 
*****************************************************************************/
 
#include <sys/types.h>
 
/** @file include/buf0lru.h
 The database buffer pool LRU replacement algorithm
 
 Created 11/5/1995 Heikki Tuuri
 *******************************************************/
 
#ifndef buf0lru_h
#define buf0lru_h
 
#include "buf0types.h"
#include "univ.i"
#ifndef UNIV_HOTBACKUP
#include "ut0byte.h"
 
// Forward declaration
struct trx_t;
 
/** Returns true if less than 25 % of the buffer pool is available. This can be
 used in heuristics to prevent huge transactions eating up the whole buffer
 pool for their locks.
 @return true if less than 25 % of buffer pool left */
bool buf_LRU_buf_pool_running_out(void);
 
/*#######################################################################
These are low-level functions
#########################################################################*/
 
/** Minimum LRU list length for which the LRU_old pointer is defined
8 megabytes of 16k pages */
constexpr uint32_t BUF_LRU_OLD_MIN_LEN = 8 * 1024 / 16;
#endif /* !UNIV_HOTBACKUP */
 
/** Flushes all dirty pages or removes all pages belonging to a given
tablespace. A PROBLEM: if readahead is being started, what guarantees
that it will not try to read in pages after this operation has completed?
@param[in]  id          tablespace ID
@param[in]  buf_remove  remove or flush strategy
@param[in]  trx         to check if the operation must be interrupted
@param[in]  strict      true, if no page from tablespace can be in
                        buffer pool just after flush */
void buf_LRU_flush_or_remove_pages(space_id_t id, buf_remove_t buf_remove,
                                   const trx_t *trx, bool strict = true);
 
#ifndef UNIV_HOTBACKUP
#if defined UNIV_DEBUG || defined UNIV_BUF_DEBUG
/** Insert a compressed block into buf_pool->zip_clean in the LRU order.
@param[in]      bpage   pointer to the block in question */
void buf_LRU_insert_zip_clean(buf_page_t *bpage);
#endif /* UNIV_DEBUG || UNIV_BUF_DEBUG */
 
/** Try to free a block.  If bpage is a descriptor of a compressed-only
page, the descriptor object will be freed as well.
NOTE: this function may temporarily release and relock the
buf_page_get_mutex(). Furthermore, the page frame will no longer be
accessible via bpage. If this function returns true, it will also release
the LRU list mutex.
The caller must hold the LRU list and buf_page_get_mutex() mutexes.
@param[in]      bpage   block to be freed
@param[in]      zip     true if should remove also the compressed page of
                        an uncompressed page
@return true if freed, false otherwise. */
[[nodiscard]] bool buf_LRU_free_page(buf_page_t *bpage, bool zip);
 
/** Try to free a replaceable block.
@param[in,out]  buf_pool        buffer pool instance
@param[in]      scan_all        scan whole LRU list if true, otherwise scan
                                only BUF_LRU_SEARCH_SCAN_THRESHOLD blocks
@return true if found and freed */
[[nodiscard]] bool buf_LRU_scan_and_free_block(buf_pool_t *buf_pool,
                                               bool scan_all);
 
/** Returns a free block from the buf_pool.  The block is taken off the
free list.  If it is empty, returns NULL.
@param[in]      buf_pool        buffer pool instance
@return a free control block, or NULL if the buf_block->free list is empty */
buf_block_t *buf_LRU_get_free_only(buf_pool_t *buf_pool);
 
/** Returns a free block from the buf_pool. The block is taken off the
free list. If free list is empty, blocks are moved from the end of the
LRU list to the free list.
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 free list, success:done
  * if buf_pool->try_LRU_scan is set
    * scan LRU up to srv_LRU_scan_depth to find a clean block
    * the above will put the block on free list
    * success:retry the free list
  * flush one dirty page from tail of LRU to disk
    * the above will put the block on free list
    * success: retry the free list
* iteration 1:
  * same as iteration 0 except:
    * scan whole LRU list
    * scan LRU list even if buf_pool->try_LRU_scan is not set
* iteration > 1:
  * same as iteration 1 but sleep 10ms
@param[in,out]  buf_pool        buffer pool instance
@return the free control block, in state BUF_BLOCK_READY_FOR_USE */
[[nodiscard]] buf_block_t *buf_LRU_get_free_block(buf_pool_t *buf_pool);
 
/** Determines if the unzip_LRU list should be used for evicting a victim
instead of the general LRU list.
@param[in,out]  buf_pool        buffer pool instance
@return true if should use unzip_LRU */
bool buf_LRU_evict_from_unzip_LRU(buf_pool_t *buf_pool);
 
/** Puts a block back to the free list.
@param[in]      block   block must not contain 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 */
 
/** Adds a block to the LRU list of decompressed zip pages.
@param[in]      block   control block
@param[in]      old     true if should be put to the end of the list,
                        else put to the start */
void buf_unzip_LRU_add_block(buf_block_t *block, bool old);
 
/** Moves a block to the start of the LRU list.
@param[in]      bpage   control block */
void buf_LRU_make_block_young(buf_page_t *bpage);
 
/** Moves a block to the end of the LRU list.
@param[in]      bpage   control block */
void buf_LRU_make_block_old(buf_page_t *bpage);
 
/** Updates buf_pool->LRU_old_ratio.
 @return updated old_pct */
uint buf_LRU_old_ratio_update(
    uint old_pct, /*!< in: Reserve this percentage of
                  the buffer pool for "old" blocks. */
    bool adjust); /*!< in: true=adjust the LRU list;
                   false=just assign buf_pool->LRU_old_ratio
                   during the initialization of InnoDB */
/** Update the historical stats that we are collecting for LRU eviction
 policy at the end of each interval. */
void buf_LRU_stat_update(void);
 
/** Remove one page from LRU list and put it to free list. The caller must hold
the LRU list and block mutexes and have page hash latched in X. The latch and
the block mutexes will be released.
@param[in,out]  bpage           block, must contain a file page and
                                be in a state where it can be freed; there
                                may or may not be a hash index to the page
@param[in]      ignore_content  true if should ignore page content, since it
                                could be not initialized */
void buf_LRU_free_one_page(buf_page_t *bpage, bool ignore_content);
 
/** Adjust LRU hazard pointers if needed.
@param[in] buf_pool Buffer pool instance
@param[in] bpage Control block */
void buf_LRU_adjust_hp(buf_pool_t *buf_pool, const buf_page_t *bpage);
 
#if defined UNIV_DEBUG || defined UNIV_BUF_DEBUG
/** Validates the LRU list. */
void buf_LRU_validate(void);
 
/** Validates the LRU list for one buffer pool instance.
@param[in]      buf_pool        buffer pool instance */
void buf_LRU_validate_instance(buf_pool_t *buf_pool);
 
using Space_References = std::map<struct fil_space_t *, size_t>;
 
/** Counts number of pages that are still in the LRU  for each space instance
encountered.
@returns map of space instances into count of pages in LRU. */
Space_References buf_LRU_count_space_references();
 
#endif /* UNIV_DEBUG || UNIV_BUF_DEBUG */
#if defined UNIV_DEBUG_PRINT || defined UNIV_DEBUG || defined UNIV_BUF_DEBUG
/** Prints the LRU list. */
void buf_LRU_print(void);
#endif /* UNIV_DEBUG_PRINT || UNIV_DEBUG || UNIV_BUF_DEBUG */
 
/** @name Heuristics for detecting index scan
@{ */
/** The denominator of buf_pool->LRU_old_ratio. */
constexpr uint32_t 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 */
constexpr uint32_t 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. */
constexpr uint32_t BUF_LRU_OLD_RATIO_MIN = 51;
 
static_assert(BUF_LRU_OLD_RATIO_MIN < BUF_LRU_OLD_RATIO_MAX,
              "BUF_LRU_OLD_RATIO_MIN >= BUF_LRU_OLD_RATIO_MAX");
static_assert(BUF_LRU_OLD_RATIO_MAX <= BUF_LRU_OLD_RATIO_DIV,
              "BUF_LRU_OLD_RATIO_MAX > BUF_LRU_OLD_RATIO_DIV");
 
/** 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. */
std::chrono::milliseconds get_buf_LRU_old_threshold();
/** @} */
 
/** @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(). Accesses protected by memory barriers. */
extern buf_LRU_stat_t buf_LRU_stat_sum;
 
/** Increments the I/O counter in buf_LRU_stat_cur. */
inline void buf_LRU_stat_inc_io() { buf_LRU_stat_cur.io++; }
/** Increments the page_zip_decompress() counter in buf_LRU_stat_cur. */
inline void buf_LRU_stat_inc_unzip() { buf_LRU_stat_cur.unzip++; }
 
#endif /* !UNIV_HOTBACKUP */
 
#endif