简单数据库实现——Part11 - 递归搜索B树
上一部分我们遇到了一个错误:
db > insert 15 user15 [email protected]
Need to implement searching an internal node
首先,将报错部分代码替换成新的函数调用。
if (get_node_type(root_node) == NODE_LEAF) {
return leaf_node_find(table, root_page_num, key);
} else {
- printf("Need to implement searching an internal node\n");
- exit(EXIT_FAILURE);
+ return internal_node_find(table, root_page_num, key);
}
}
这个函数会进行二分查找,找到包含给定键(key)的孩子元素。记住每个子指针右边的键是子指针包含的最大键。
所以,我们的二分查找比较待查键和子指针右边的键。
+Cursor* internal_node_find(Table* table, uint32_t page_num, uint32_t key) {
+ void* node = get_page(table->pager, page_num);
+ uint32_t num_keys = *internal_node_num_keys(node);
+
+ /* Binary search to find index of child to search */
+ uint32_t min_index = 0;
+ uint32_t max_index = num_keys; /* there is one more child than key */
+
+ while (min_index != max_index) {
+ uint32_t index = (min_index + max_index) / 2;
+ uint32_t key_to_right = *internal_node_key(node, index);
+ if (key_to_right >= key) {
+ max_index = index;
+ } else {
+ min_index = index + 1;
+ }
+ }
请记住内部节点的孩子可以是内部节点也可以是叶节点。当我们找到了正确的孩子,调用相应的搜索函数。
+ uint32_t child_num = *internal_node_child(node, min_index);
+ void* child = get_page(table->pager, child_num);
+ switch (get_node_type(child)) {
+ case NODE_LEAF:
+ return leaf_node_find(table, child_num, key);
+ case NODE_INTERNAL:
+ return internal_node_find(table, child_num, key);
+ }
+}
现在,将key插入多节点B树将不再错误,我们可以更新测试:
" - 12",
" - 13",
" - 14",
- "db > Need to implement searching an internal node",
+ "db > Executed.",
+ "db > ",
])
end
这个时候还可以补充一个新测试。尝试插入1400行,这依然是错误的,但是错误消息应该更新。
raw_output = nil
IO.popen("./db test.db", "r+") do |pipe|
commands.each do |command|
- pipe.puts command
+ begin
+ pipe.puts command
+ rescue Errno::EPIPE
+ break
+ end
end
pipe.close_write
这表明我们的1400行测试输出错误。
end
script << ".exit"
result = run_script(script)
- expect(result[-2]).to eq('db > Error: Table full.')
+ expect(result.last(2)).to match_array([
+ "db > Executed.",
+ "db > Need to implement updating parent after split",
+ ])
end