Btr Cur Latch Leaves: Locking Leaf Pages in InnoDB

/**

• Latches the leaf page or pages requested. / static void btr_cur_latch_leaves( /=================/ page_t page, /!< in: leaf page where the search converged / ulint space, /!< in: space id / ulint zip_size, /!< in: compressed page size in bytes or 0 for uncompressed pages / ulint page_no, /!< in: page number of the leaf / ulint latch_mode, /!< in: BTR_SEARCH_LEAF, ... / btr_cur_t cursor, /!< in: cursor / mtr_t mtr) /*!< in: mtr / { ulint mode; ulint left_page_no; ulint right_page_no; buf_block_t get_block;

  ut_ad(page && mtr);

  switch (latch_mode) { case BTR_SEARCH_LEAF: case BTR_MODIFY_LEAF: mode = latch_mode == BTR_SEARCH_LEAF ? RW_S_LATCH : RW_X_LATCH; get_block = btr_block_get(space, zip_size, page_no, mode, mtr); #ifdef UNIV_BTR_DEBUG ut_a(page_is_comp(get_block->frame) == page_is_comp(page)); #endif /* UNIV_BTR_DEBUG / get_block->check_index_page_at_flush = TRUE; return; case BTR_MODIFY_TREE: / x-latch also brothers from left to right */ left_page_no = btr_page_get_prev(page, mtr);

   if (left_page_no != FIL_NULL) {
   	get_block = btr_block_get(space, zip_size,
   						  left_page_no,
   						  RW_X_LATCH, mtr);
  

#ifdef UNIV_BTR_DEBUG ut_a(page_is_comp(get_block->frame) == page_is_comp(page)); ut_a(btr_page_get_next(get_block->frame, mtr) == page_get_page_no(page)); #endif /* UNIV_BTR_DEBUG */ get_block->check_index_page_at_flush = TRUE; }

	get_block = btr_block_get(space, zip_size, page_no,
					  RW_X_LATCH, mtr);

#ifdef UNIV_BTR_DEBUG ut_a(page_is_comp(get_block->frame) == page_is_comp(page)); #endif /* UNIV_BTR_DEBUG */ get_block->check_index_page_at_flush = TRUE;

	right_page_no = btr_page_get_next(page, mtr);

	if (right_page_no != FIL_NULL) {
		get_block = btr_block_get(space, zip_size,
						  right_page_no,
						  RW_X_LATCH, mtr);

#ifdef UNIV_BTR_DEBUG ut_a(page_is_comp(get_block->frame) == page_is_comp(page)); ut_a(btr_page_get_prev(get_block->frame, mtr) == page_get_page_no(page)); #endif /* UNIV_BTR_DEBUG */ get_block->check_index_page_at_flush = TRUE; }

	return;

case BTR_SEARCH_PREV:
case BTR_MODIFY_PREV:
	mode = latch_mode == BTR_SEARCH_PREV ? RW_S_LATCH : RW_X_LATCH;
	/* latch also left brother */
	left_page_no = btr_page_get_prev(page, mtr);

	if (left_page_no != FIL_NULL) {
		get_block = btr_block_get(space, zip_size,
						  left_page_no, mode, mtr);
		cursor->left_block = get_block;

#ifdef UNIV_BTR_DEBUG ut_a(page_is_comp(get_block->frame) == page_is_comp(page)); ut_a(btr_page_get_next(get_block->frame, mtr) == page_get_page_no(page)); #endif /* UNIV_BTR_DEBUG */ get_block->check_index_page_at_flush = TRUE; }

	get_block = btr_block_get(space, zip_size, page_no, mode, mtr);

#ifdef UNIV_BTR_DEBUG ut_a(page_is_comp(get_block->frame) == page_is_comp(page)); #endif /* UNIV_BTR_DEBUG */ get_block->check_index_page_at_flush = TRUE; return; }

ut_error;

}

代码分析内容：该函数用于对所需的叶子页进行锁定。

函数参数解析：

• page：叶子页，搜索结束后的页。
• space：页所在表空间的ID。
• zip_size：页的压缩大小（如果未压缩，则为0）。
• page_no：页号。
• latch_mode：表示锁定模式（BTR_SEARCH_LEAF，BTR_MODIFY_LEAF，BTR_MODIFY_TREE，BTR_SEARCH_PREV，BTR_MODIFY_PREV）。
• cursor：游标。
• mtr：Mini-Transaction。

根据不同的锁定模式，函数的处理方式也不同。

• BTR_SEARCH_LEAF 和 BTR_MODIFY_LEAF：对叶子页进行S锁或X锁。
• BTR_MODIFY_TREE：对兄弟页进行X锁，并对叶子页进行X锁。
• BTR_SEARCH_PREV 和 BTR_MODIFY_PREV：对左兄弟页进行S锁或X锁，并对叶子页进行S锁或X锁。

最后，该函数会设置一个标志，表示在刷新缓冲池时需要检查该页是否是索引页。