Innodb_buffer_pool_read_requests探究之路

ulint innodb_buffer_pool_read_requests;    /*!< buf_pool->stat.n_page_gets */

/******************************************************************//**
Function to pass InnoDB status variables to MySQL */
void
srv_export_innodb_status(void)
/*==========================*/
{
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    export_vars.innodb_buffer_pool_read_requests = stat.n_page_gets;
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}

/* innodb_buffer_pool_read_requests, the number of logical
read requests */
case MONITOR_OVLD_BUF_POOL_READ_REQUESTS:
    buf_get_total_stat(&stat);
    value = stat.n_page_gets;
    break;

/** @brief The buffer pool statistics structure. */
struct buf_pool_stat_t{
    ulint   n_page_gets;    /*!< number of page gets performed;
                also successful searches through
                the adaptive hash index are
                counted as page gets; this field
                is NOT protected by the buffer
                pool mutex */
    省略部分代码
};

mysql> show create table t1;
+-------+---------------------------------------------------------------------------------------+
| Table | Create Table                                                                          |
+-------+---------------------------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (
  `a` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+---------------------------------------------------------------------------------------+
mysql> insert into t1() values(1),(2),(10),(11),(12);
mysql> select * from t1;
mysql> select * from t1 limit 2;
mysql> select * from t1 limit 3;
mysql> select * from t1 limit 4;
mysql> select * from t1 where a=1;

/** This is the general function used to get access to a database page.
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@return pointer to the block or NULL */
buf_block_t*
buf_page_get_gen(const page_id_t&    page_id,省略部分代码)
{
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    buf_pool->stat.n_page_gets++;
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}

This is the general function used to get optimistic access to a database page.
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buf_page_optimistic_get(buf_block_t*    block,  /*!< in: guessed buffer block */
/*====================*/
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{
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    buf_pool->stat.n_page_gets++;
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}

/**
  Read next row via random scan.

  @param buf  Buffer to read the row into

  @return Operation status
    @retval 0     Success
    @retval != 0  Error (error code returned)
*/

int handler::ha_rnd_next(uchar *buf)
{
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}

/**********************************************************************//**
Positions an index cursor to the index specified in the handle. Fetches the
row if any.
@return 0, HA_ERR_KEY_NOT_FOUND, or error number */

int
ha_innobase::index_read(
/*====================*/
    uchar*      buf,        /*!< in/out: buffer for the returned
                    row */
    const uchar*    key_ptr,    /*!< in: key value; if this is NULL
                    we position the cursor at the
                    start or end of index; this can
                    also contain an InnoDB row id, in
                    which case key_len is the InnoDB
                    row id length; the key value can
                    also be a prefix of a full key value,
                    and the last column can be a prefix
                    of a full column */
    uint            key_len,/*!< in: key value length */
    enum ha_rkey_function find_flag)/*!< in: search flags from my_base.h */
{
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}

/***********************************************************************//**
Reads the next or previous row from a cursor, which must have previously been
positioned using index_read.
@return 0, HA_ERR_END_OF_FILE, or error number */

int
ha_innobase::general_fetch(
/*=======================*/
    uchar*  buf,        /*!< in/out: buffer for next row in MySQL
                format */
    uint    direction,  /*!< in: ROW_SEL_NEXT or ROW_SEL_PREV */
    uint    match_mode) /*!< in: 0, ROW_SEL_EXACT, or
                ROW_SEL_EXACT_PREFIX */
{
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}