buf0rea.h

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/** @file include/buf0rea.h
 The database buffer read
 
 Created 11/5/1995 Heikki Tuuri
 *******************************************************/
 
#ifndef buf0rea_h
#define buf0rea_h
 
#include "buf0buf.h"
#include "buf0types.h"
 
/** Low-level function which reads a page asynchronously from a file to the
buffer buf_pool if it is not already there, in which case does nothing.
Sets the io_fix flag and sets an exclusive lock on the buffer frame. The
flag is cleared and the x-lock released by an i/o-handler thread.
@param[out]     err             DB_SUCCESS or DB_TABLESPACE_DELETED
                                if we are trying to read from a non-existent
                                tablespace or a tablespace which is just now
                                being dropped
@param[in]      sync            whether synchronous aio is desired
@param[in]      type            Request type
@param[in]      mode            BUF_READ_IBUF_PAGES_ONLY, ...
@param[in]      page_id         page id
@param[in]      page_size       page size
@param[in]      unzip           true=request uncompressed page
@return 1 if a read request was queued, 0 if the page already resided in
buf_pool, or if the page is in the doublewrite buffer blocks in which case it
is never read into the pool, or if the tablespace does not exist or is being
dropped */
ulint buf_read_page_low(dberr_t *err, bool sync, ulint type, ulint mode,
                        const page_id_t &page_id, const page_size_t &page_size,
                        bool unzip);
 
/** High-level function which reads a page asynchronously from a file to the
buffer buf_pool if it is not already there. Sets the io_fix flag and sets
an exclusive lock on the buffer frame. The flag is cleared and the x-lock
released by the i/o-handler thread.
@param[in]      page_id         page id
@param[in]      page_size       page size
@return true if page has been read in, false in case of failure */
bool buf_read_page(const page_id_t &page_id, const page_size_t &page_size);
 
/** High-level function which reads a page asynchronously from a file to the
buffer buf_pool if it is not already there. Sets the io_fix flag and sets
an exclusive lock on the buffer frame. The flag is cleared and the x-lock
released by the i/o-handler thread.
@param[in]      page_id         page id
@param[in]      page_size       page size
@param[in]      sync            true if synchronous aio is desired
@return true if page has been read in, false in case of failure */
bool buf_read_page_background(const page_id_t &page_id,
                              const page_size_t &page_size, bool sync);
 
/** Applies a random read-ahead in buf_pool if there are at least a threshold
value of accessed pages from the random read-ahead area. Does not read any
page, not even the one at the position (space, offset), if the read-ahead
mechanism is not activated. NOTE 1: the calling thread may own latches on
pages: to avoid deadlocks this function must be written such that it cannot
end up waiting for these latches! NOTE 2: the calling thread must want
access to the page given: this rule is set to prevent unintended read-aheads
performed by ibuf routines, a situation which could result in a deadlock if
the OS does not support asynchronous i/o.
@param[in]      page_id         page id of a page which the current thread
wants to access
@param[in]      page_size       page size
@param[in]      inside_ibuf     true if we are inside ibuf routine
@return number of page read requests issued; NOTE that if we read ibuf
pages, it may happen that the page at the given page number does not
get read even if we return a positive value! */
ulint buf_read_ahead_random(const page_id_t &page_id,
                            const page_size_t &page_size, bool inside_ibuf);
 
/** Applies linear read-ahead if in the buf_pool the page is a border page of
a linear read-ahead area and all the pages in the area have been accessed.
Does not read any page if the read-ahead mechanism is not activated. Note
that the algorithm looks at the 'natural' adjacent successor and
predecessor of the page, which on the leaf level of a B-tree are the next
and previous page in the chain of leaves. To know these, the page specified
in (space, offset) must already be present in the buf_pool. Thus, the
natural way to use this function is to call it when a page in the buf_pool
is accessed the first time, calling this function just after it has been
bufferfixed.
NOTE 1: as this function looks at the natural predecessor and successor
fields on the page, what happens, if these are not initialized to any
sensible value? No problem, before applying read-ahead we check that the
area to read is within the span of the space, if not, read-ahead is not
applied. An uninitialized value may result in a useless read operation, but
only very improbably.
NOTE 2: the calling thread may own latches on pages: to avoid deadlocks this
function must be written such that it cannot end up waiting for these
latches!
NOTE 3: the calling thread must want access to the page given: this rule is
set to prevent unintended read-aheads performed by ibuf routines, a situation
which could result in a deadlock if the OS does not support asynchronous io.
@param[in]      page_id         page id; see NOTE 3 above
@param[in]      page_size       page size
@param[in]      inside_ibuf     true if we are inside ibuf routine
@return number of page read requests issued */
ulint buf_read_ahead_linear(const page_id_t &page_id,
                            const page_size_t &page_size, bool inside_ibuf);
 
/** Issues read requests for pages which the ibuf module wants to read in, in
order to contract the insert buffer tree. Technically, this function is like
a read-ahead function.
@param[in] sync                 true if the caller wants this function to wait
                                for the highest address page to get read in,
                                before this function returns.
@param[in] space_ids            Array of space ids.
@param[in] page_nos             Array of page numbers to read, with the highest
                                page number the last in the array.
@param[in] n_stored             number of elements in the arrays. */
void buf_read_ibuf_merge_pages(bool sync, const space_id_t *space_ids,
                               const page_no_t *page_nos, ulint n_stored);
 
/** Issues asynchronous read requests for pages which recovery wants to read in.
@param[in]      space_id        tablespace id
@param[in]      page_nos        array of page numbers to read, with the
highest page number the last in the array
@param[in]      n_stored        number of page numbers in the array */
 
void buf_read_recv_pages(space_id_t space_id, const page_no_t *page_nos,
                         ulint n_stored);
 
/** @name Modes used in read-ahead
@{ */
/** read only pages belonging to the insert buffer tree */
constexpr uint32_t BUF_READ_IBUF_PAGES_ONLY = 131;
/** read any page */
constexpr uint32_t BUF_READ_ANY_PAGE = 132;
/** @} */
 
#endif