/********************************************************************//**
This is the general function used to get access to a database page.
@return pointer to the block or NULL */
UNIV_INTERN
buf_block_t*
buf_page_get_gen(
/*=============*/
ulint space, /*!< in: space id */
ulint zip_size,/*!< in: compressed page size in bytes
or 0 for uncompressed pages */
ulint offset, /*!< in: page number */
ulint rw_latch,/*!< in: RW_S_LATCH, RW_X_LATCH, RW_NO_LATCH */
buf_block_t* guess, /*!< in: guessed block or NULL */
ulint mode, /*!< in: BUF_GET, BUF_GET_IF_IN_POOL,
BUF_PEEK_IF_IN_POOL, BUF_GET_NO_LATCH, or
BUF_GET_IF_IN_POOL_OR_WATCH */
const char* file, /*!< in: file name */
ulint line, /*!< in: line where called */
mtr_t* mtr) /*!< in: mini-transaction */
{
buf_block_t* block;
ulint fold;
unsigned access_time;
ulint fix_type;
ibool must_read;
ulint retries = 0;
buf_pool_t* buf_pool = buf_pool_get(space, offset);
ut_ad(mtr);
ut_ad(mtr->state == MTR_ACTIVE);
ut_ad((rw_latch == RW_S_LATCH)
|| (rw_latch == RW_X_LATCH)
|| (rw_latch == RW_NO_LATCH));
ut_ad(zip_size == fil_space_get_zip_size(space));
ut_ad(ut_is_2pow(zip_size));
buf_pool->stat.n_page_gets++;
fold = buf_page_address_fold(space, offset);
loop:
block = guess; //guess 为 NULL
buf_pool_mutex_enter(buf_pool);
if (block) {
//这里不进来，因为block为空 /* If the guess is a compressed page descriptor that
has been allocated by buf_page_alloc_descriptor(),
it may have been freed by buf_relocate(). */
if (!buf_block_is_uncompressed(buf_pool, block)
|| offset != block->page.offset
|| space != block->page.space
|| buf_block_get_state(block) != BUF_BLOCK_FILE_PAGE) {
block = guess = NULL;
} else {
ut_ad(!block->page.in_zip_hash);
ut_ad(block->page.in_page_hash);
}
}
if (block == NULL) {
/**
*详见
*从buf_pool->page_hash中找到相应page
*当找到的page->offset == offset时,返回page
*
*/
block = (buf_block_t*) buf_page_hash_get_low(buf_pool, space, offset, fold);
}
if (block && buf_pool_watch_is_sentinel(buf_pool, &block->page)) {
block = NULL;
}
if (block == NULL) {
/* Page not in buf_pool: needs to be read from file */
//如果hash表中没有找到block,就读取硬盘文件
if (mode == BUF_GET_IF_IN_POOL_OR_WATCH) {
block = (buf_block_t*) buf_pool_watch_set(space, offset, fold);
if (UNIV_LIKELY_NULL(block)) {
goto got_block;
}
}
buf_pool_mutex_exit(buf_pool);
if (mode == BUF_GET_IF_IN_POOL
|| mode == BUF_PEEK_IF_IN_POOL
|| mode == BUF_GET_IF_IN_POOL_OR_WATCH) {
return(NULL);
}
if (buf_read_page(space, zip_size, offset)) {//从硬盘中读取数据，并开始预读,详见
buf_read_ahead_random(space, zip_size, offset,ibuf_inside(mtr));
retries = 0;
} else if (retries < BUF_PAGE_READ_MAX_RETRIES) {
++retries;
DBUG_EXECUTE_IF(
"innodb_page_corruption_retries",
retries = BUF_PAGE_READ_MAX_RETRIES;
);
} else {
fprintf(stderr, "InnoDB: Error: Unable"
" to read tablespace %lu page no"
" %lu into the buffer pool after"
" %lu attempts\n"
"InnoDB: The most probable cause"
" of this error may be that the"
" table has been corrupted.\n"
"InnoDB: You can try to fix this"
" problem by using"
" innodb_force_recovery.\n"
"InnoDB: Please see reference manual"
" for more details.\n"
"InnoDB: Aborting...\n",
space, offset,
BUF_PAGE_READ_MAX_RETRIES);
ut_error;
}
#if defined UNIV_DEBUG || defined UNIV_BUF_DEBUG
ut_a(++buf_dbg_counter % 5771 || buf_validate());
#endif /* UNIV_DEBUG || UNIV_BUF_DEBUG */
goto loop;
}
got_block:
ut_ad(page_zip_get_size(&block->page.zip) == zip_size);
must_read = buf_block_get_io_fix(block) == BUF_IO_READ;
if (must_read && (mode == BUF_GET_IF_IN_POOL
|| mode == BUF_PEEK_IF_IN_POOL)) {
/* The page is being read to buffer pool,
but we cannot wait around for the read to
complete. */
null_exit:
buf_pool_mutex_exit(buf_pool);
return(NULL);
}
switch (buf_block_get_state(block)) {
buf_page_t* bpage;
ibool success;
case BUF_BLOCK_FILE_PAGE:
break;
case BUF_BLOCK_ZIP_PAGE:
case BUF_BLOCK_ZIP_DIRTY:
if (mode == BUF_PEEK_IF_IN_POOL) {
/* This mode is only used for dropping an
adaptive hash index. There cannot be an
adaptive hash index for a compressed-only
page, so do not bother decompressing the page. */
goto null_exit;
}
bpage = &block->page;
/* Protect bpage->buf_fix_count. */
mutex_enter(&buf_pool->zip_mutex);
if (bpage->buf_fix_count
|| buf_page_get_io_fix(bpage) != BUF_IO_NONE) {
/* This condition often occurs when the buffer
is not buffer-fixed, but I/O-fixed by
buf_page_init_for_read(). */
mutex_exit(&buf_pool->zip_mutex);
wait_until_unfixed:
/* The block is buffer-fixed or I/O-fixed.
Try again later. */
buf_pool_mutex_exit(buf_pool);
os_thread_sleep(WAIT_FOR_READ);
goto loop;
}
/* Buffer-fix the block so that it cannot be evicted
or relocated while we are attempting to allocate an
uncompressed page. */
bpage->buf_fix_count++;
/* Allocate an uncompressed page. */
buf_pool_mutex_exit(buf_pool);
mutex_exit(&buf_pool->zip_mutex);
block = buf_LRU_get_free_block(buf_pool);
ut_a(block);
buf_pool_mutex_enter(buf_pool);
mutex_enter(&block->mutex);
mutex_enter(&buf_pool->zip_mutex);
/* Buffer-fixing prevents the page_hash from changing. */
ut_ad(bpage == buf_page_hash_get_low(buf_pool,
space, offset, fold));
if (--bpage->buf_fix_count
|| buf_page_get_io_fix(bpage) != BUF_IO_NONE) {
mutex_exit(&buf_pool->zip_mutex);
/* The block was buffer-fixed or I/O-fixed while
buf_pool->mutex was not held by this thread.
Free the block that was allocated and retry.
This should be extremely unlikely, for example,
if buf_page_get_zip() was invoked. */
buf_LRU_block_free_non_file_page(block);
mutex_exit(&block->mutex);
goto wait_until_unfixed;
}
/* Move the compressed page from bpage to block,
and uncompress it. */
buf_relocate(bpage, &block->page);
buf_block_init_low(block);
block->lock_hash_val = lock_rec_hash(space, offset);
UNIV_MEM_DESC(&block->page.zip.data,
page_zip_get_size(&block->page.zip), block);
if (buf_page_get_state(&block->page)
== BUF_BLOCK_ZIP_PAGE) {
#if defined UNIV_DEBUG || defined UNIV_BUF_DEBUG
UT_LIST_REMOVE(list, buf_pool->zip_clean,
&block->page);
#endif /* UNIV_DEBUG || UNIV_BUF_DEBUG */
ut_ad(!block->page.in_flush_list);
} else {
/* Relocate buf_pool->flush_list. */
buf_flush_relocate_on_flush_list(bpage,
&block->page);
}
/* Buffer-fix, I/O-fix, and X-latch the block
for the duration of the decompression.
Also add the block to the unzip_LRU list. */
block->page.state = BUF_BLOCK_FILE_PAGE;
/* Insert at the front of unzip_LRU list */
buf_unzip_LRU_add_block(block, FALSE);
block->page.buf_fix_count = 1;
buf_block_set_io_fix(block, BUF_IO_READ);
rw_lock_x_lock_inline(&block->lock, 0, file, line);
UNIV_MEM_INVALID(bpage, sizeof *bpage);
buf_pool->n_pend_unzip++;
mutex_exit(&buf_pool->zip_mutex);
buf_pool_mutex_exit(buf_pool);
access_time = buf_page_is_accessed(&block->page);
mutex_exit(&block->mutex);
buf_page_free_descriptor(bpage);
/* Decompress the page while not holding
buf_pool->mutex or block->mutex. */
success = buf_zip_decompress(block, srv_use_checksums);
ut_a(success);
if (UNIV_LIKELY(!recv_no_ibuf_operations)) {
if (access_time) {
#ifdef UNIV_IBUF_COUNT_DEBUG
ut_a(ibuf_count_get(space, offset) == 0);
#endif /* UNIV_IBUF_COUNT_DEBUG */
} else {
ibuf_merge_or_delete_for_page(
block, space, offset, zip_size, TRUE);
}
}
/* Unfix and unlatch the block. */
buf_pool_mutex_enter(buf_pool);
mutex_enter(&block->mutex);
block->page.buf_fix_count--;
buf_block_set_io_fix(block, BUF_IO_NONE);
mutex_exit(&block->mutex);
buf_pool->n_pend_unzip--;
rw_lock_x_unlock(&block->lock);
break;
case BUF_BLOCK_ZIP_FREE:
case BUF_BLOCK_NOT_USED:
case BUF_BLOCK_READY_FOR_USE:
case BUF_BLOCK_MEMORY:
case BUF_BLOCK_REMOVE_HASH:
ut_error;
break;
}
ut_ad(buf_block_get_state(block) == BUF_BLOCK_FILE_PAGE);
mutex_enter(&block->mutex);
#if UNIV_WORD_SIZE == 4
/* On 32-bit systems, there is no padding in buf_page_t. On
other systems, Valgrind could complain about uninitialized pad
bytes. */
UNIV_MEM_ASSERT_RW(&block->page, sizeof block->page);
#endif
#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
if ((mode == BUF_GET_IF_IN_POOL || mode == BUF_GET_IF_IN_POOL_OR_WATCH)
&& ibuf_debug) {
/* Try to evict the block from the buffer pool, to use the
insert buffer (change buffer) as much as possible. */
if (buf_LRU_free_block(&block->page, TRUE)) {
mutex_exit(&block->mutex);
if (mode == BUF_GET_IF_IN_POOL_OR_WATCH) {
/* Set the watch, as it would have
been set if the page were not in the
buffer pool in the first place. */
block = (buf_block_t*) buf_pool_watch_set(
space, offset, fold);
if (UNIV_LIKELY_NULL(block)) {
/* The page entered the buffer
pool for some reason. Try to
evict it again. */
goto got_block;
}
}
buf_pool_mutex_exit(buf_pool);
fprintf(stderr,
"innodb_change_buffering_debug evict %u %u\n",
(unsigned) space, (unsigned) offset);
return(NULL);
} else if (buf_flush_page_try(buf_pool, block)) {
fprintf(stderr,
"innodb_change_buffering_debug flush %u %u\n",
(unsigned) space, (unsigned) offset);
guess = block;
goto loop;
}
/* Failed to evict the page; change it directly */
}
#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
buf_block_buf_fix_inc(block, file, line);
#if defined UNIV_DEBUG_FILE_ACCESSES || defined UNIV_DEBUG
ut_a(mode == BUF_GET_POSSIBLY_FREED
|| !block->page.file_page_was_freed);
#endif
buf_pool_mutex_exit(buf_pool);
/* Check if this is the first access to the page */
access_time = buf_page_is_accessed(&block->page);
buf_page_set_accessed(&block->page);
mutex_exit(&block->mutex);
if (mode != BUF_PEEK_IF_IN_POOL) {
buf_page_make_young_if_needed(&block->page);
}
#if defined UNIV_DEBUG || defined UNIV_BUF_DEBUG
ut_a(++buf_dbg_counter % 5771 || buf_validate());
ut_a(block->page.buf_fix_count > 0);
ut_a(buf_block_get_state(block) == BUF_BLOCK_FILE_PAGE);
#endif /* UNIV_DEBUG || UNIV_BUF_DEBUG */
switch (rw_latch) {
case RW_NO_LATCH:
if (must_read) {
/* Let us wait until the read operation
completes */
for (;;) {
enum buf_io_fix io_fix;
mutex_enter(&block->mutex);
io_fix = buf_block_get_io_fix(block);
mutex_exit(&block->mutex);
if (io_fix == BUF_IO_READ) {
/* wait by temporaly s-latch */
rw_lock_s_lock(&(block->lock));
rw_lock_s_unlock(&(block->lock));
} else {
break;
}
}
}
fix_type = MTR_MEMO_BUF_FIX;
break;
case RW_S_LATCH:
rw_lock_s_lock_inline(&(block->lock), 0, file, line);
fix_type = MTR_MEMO_PAGE_S_FIX;
break;
default:
ut_ad(rw_latch == RW_X_LATCH);
rw_lock_x_lock_inline(&(block->lock), 0, file, line);
fix_type = MTR_MEMO_PAGE_X_FIX;
break;
}
mtr_memo_push(mtr, block, fix_type);
if (mode != BUF_PEEK_IF_IN_POOL && !access_time) {
/* In the case of a first access, try to apply linear
read-ahead */
buf_read_ahead_linear(space, zip_size, offset,
ibuf_inside(mtr));
}
#ifdef UNIV_IBUF_COUNT_DEBUG
ut_a(ibuf_count_get(buf_block_get_space(block),
buf_block_get_page_no(block)) == 0);
#endif
return(block);
}
