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/*****************************************************************************
Copyright (c) 1995, 2017, 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/buf0dblwr.h
Doublewrite buffer module
Created 2011/12/19 Inaam Rana
*******************************************************/
#pragma once
#include "os0file.h"
#include "buf0types.h"
/** Doublewrite control struct */
class buf_dblwr_t
{
struct element
{
/** asynchronous write request */
IORequest request;
/** payload size in bytes */
size_t size;
};
struct slot
{
/** first free position in write_buf measured in units of
* srv_page_size */
ulint first_free;
/** number of slots reserved for the current write batch */
ulint reserved;
/** the doublewrite buffer, aligned to srv_page_size */
byte* write_buf;
/** buffer blocks to be written via write_buf */
element* buf_block_arr;
};
/** the page number of the first doublewrite block (block_size pages) */
page_id_t block1{0, 0};
/** the page number of the second doublewrite block (block_size pages) */
page_id_t block2{0, 0};
/** mutex protecting the data members below */
mysql_mutex_t mutex;
/** condition variable for !batch_running */
pthread_cond_t cond;
/** whether a batch is being written from the doublewrite buffer */
bool batch_running;
/** number of expected flush_buffered_writes_completed() calls */
unsigned flushing_buffered_writes;
/** number of flush_buffered_writes_completed() calls */
ulint writes_completed;
/** number of pages written by flush_buffered_writes_completed() */
ulint pages_written;
slot slots[2];
slot *active_slot;
/** Size of the doublewrite block in pages */
uint32_t block_size;
public:
/** Values of use */
enum usage {
/** Assume that writes are atomic */
USE_NO= 0,
/** Use the doublewrite buffer with full durability */
USE_YES,
/** Durable writes to the doublewrite buffer, not to data files */
USE_FAST
};
/** The value of innodb_doublewrite */
ulong use;
private:
/** Initialise the persistent storage of the doublewrite buffer.
@param header doublewrite page header in the TRX_SYS page */
inline void init(const byte *header);
/** Flush possible buffered writes to persistent storage. */
bool flush_buffered_writes(const ulint size);
public:
/** Initialise the doublewrite buffer data structures. */
void init();
/** Create or restore the doublewrite buffer in the TRX_SYS page.
@return whether the operation succeeded */
bool create();
/** Free the doublewrite buffer. */
void close();
/** Acquire the mutex */
void lock() { mysql_mutex_lock(&mutex); }
/** @return the number of completed batches */
ulint batches() const
{ mysql_mutex_assert_owner(&mutex); return writes_completed; }
/** @return the number of final pages written */
ulint written() const
{ mysql_mutex_assert_owner(&mutex); return pages_written; }
/** Release the mutex */
void unlock() { mysql_mutex_unlock(&mutex); }
/** Initialize the doublewrite buffer memory structure on recovery.
If we are upgrading from a version before MySQL 4.1, then this
function performs the necessary update operations to support
innodb_file_per_table. If we are in a crash recovery, this function
loads the pages from double write buffer which are not older than
the checkpoint into memory.
@param file File handle
@param path Path name of file
@return DB_SUCCESS or error code */
dberr_t init_or_load_pages(pfs_os_file_t file, const char *path);
/** Process and remove the double write buffer pages for all tablespaces. */
void recover();
/** Update the doublewrite buffer on data page write completion. */
void write_completed();
/** Flush possible buffered writes to persistent storage.
It is very important to call this function after a batch of writes has been
posted, and also when we may have to wait for a page latch!
Otherwise a deadlock of threads can occur. */
void flush_buffered_writes();
/** Update the doublewrite buffer on write batch completion
@param request the completed batch write request */
void flush_buffered_writes_completed(const IORequest &request);
/** Schedule a page write. If the doublewrite memory buffer is full,
flush_buffered_writes() will be invoked to make space.
@param request asynchronous write request
@param size payload size in bytes */
void add_to_batch(const IORequest &request, size_t size);
/** Determine whether the doublewrite buffer has been created */
bool is_created() const
{ return UNIV_LIKELY(block1 != page_id_t(0, 0)); }
/** @return whether the doublewrite buffer is in use */
bool in_use() const { return is_created() && use; }
/** @return whether fsync() is needed on non-doublewrite pages */
bool need_fsync() const { return use < USE_FAST; }
void set_use(ulong use)
{
ut_ad(use <= USE_FAST);
mysql_mutex_lock(&mutex);
this->use= use;
mysql_mutex_unlock(&mutex);
}
/** @return whether a page identifier is part of the doublewrite buffer */
bool is_inside(const page_id_t id) const
{
if (!is_created())
return false;
ut_ad(block1 < block2);
if (id < block1)
return false;
return id < block1 + block_size ||
(id >= block2 && id < block2 + block_size);
}
/** Wait for flush_buffered_writes() to be fully completed */
void wait_flush_buffered_writes()
{
mysql_mutex_lock(&mutex);
while (batch_running)
my_cond_wait(&cond, &mutex.m_mutex);
mysql_mutex_unlock(&mutex);
}
};
/** The doublewrite buffer */
extern buf_dblwr_t buf_dblwr;
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