mariadb/storage/innobase/include/buf0dblwr.h

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/**************************************************//**
@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
{
  /** the page number of the first doublewrite block (block_size() pages) */
  page_id_t block1= page_id_t(0, 0);
  /** the page number of the second doublewrite block (block_size() pages) */
  page_id_t block2= page_id_t(0, 0);

  /** mutex protecting the data members below */
  mysql_mutex_t mutex;
  /** condition variable for !batch_running */
  mysql_cond_t cond;
  /** whether a batch is being written from the doublewrite buffer */
  bool batch_running;
  /** 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;

  struct element
  {
    /** tablespace */
    fil_space_t *space;
    /** asynchronous write request */
    IORequest request;
    /** payload size in bytes */
    size_t size;
  };

  /** buffer blocks to be written via write_buf */
  element *buf_block_arr;

  /** Initialize the doublewrite buffer data structure.
  @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:
  /** Create or restore the doublewrite buffer in the TRX_SYS page.
  @return whether the operation succeeded */
  bool create();
  /** Free the doublewrite buffer. */
  void close();

  /** 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 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 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();

  /** Size of the doublewrite block in pages */
  uint32_t block_size() const { return FSP_EXTENT_SIZE; }

  /** Schedule a page write. If the doublewrite memory buffer is full,
  flush_buffered_writes() will be invoked to make space.
  @param space      tablespace
  @param request    asynchronous write request
  @param size       payload size in bytes */
  void add_to_batch(fil_space_t *space, const IORequest &request,
                    size_t size) MY_ATTRIBUTE((nonnull));

  /** Determine whether the doublewrite buffer is initialized */
  bool is_initialised() const
  { return UNIV_LIKELY(block1 != page_id_t(0, 0)); }

  /** @return whether a page identifier is part of the doublewrite buffer */
  bool is_inside(const page_id_t id) const
  {
    if (!is_initialised())
      return false;
    ut_ad(block1 < block2);
    if (id < block1)
      return false;
    const uint32_t size= block_size();
    return id < block1 + size || (id >= block2 && id < block2 + size);
  }
};

/** The doublewrite buffer */
extern buf_dblwr_t buf_dblwr;