海山数据库(He3DB)源码详解：海山Mysql 崩溃恢复（2）-日志解析

崩溃恢复之日志解析

MySQL redo日志崩溃恢复整体流程如图所示，本文将针对日志解析过程中涉及到的几个函数源码进行详细解析。

1. recv_group_scan_log_recs()函数流程

static
bool
recv_group_scan_log_recs(
	log_group_t*	group,
	lsn_t*		contiguous_lsn,
	bool		last_phase)         // 接收并扫描日志组中的日志记录
{
   
	DBUG_ENTER("recv_group_scan_log_recs");
	assert(!last_phase || recv_sys->mlog_checkpoint_lsn > 0);

	mutex_enter(&recv_sys->mutex);
	recv_sys->len = 0;
	recv_sys->recovered_offset = 0;
	recv_sys->n_addrs = 0;
	recv_sys_empty_hash();
	srv_start_lsn = *contiguous_lsn;
	recv_sys->parse_start_lsn = *contiguous_lsn;
	recv_sys->scanned_lsn = *contiguous_lsn;
	recv_sys->recovered_lsn = *contiguous_lsn;
	recv_sys->scanned_checkpoint_no = 0;
	recv_previous_parsed_rec_type = MLOG_SINGLE_REC_FLAG;
	recv_previous_parsed_rec_offset	= 0;
	recv_previous_parsed_rec_is_multi = 0;
	ut_ad(recv_max_page_lsn == 0);
	ut_ad(last_phase || !recv_writer_thread_active);
	mutex_exit(&recv_sys->mutex);

	lsn_t	checkpoint_lsn	= *contiguous_lsn;
	lsn_t	start_lsn;
	lsn_t	end_lsn;
	store_t	store_to_hash	= last_phase ? STORE_IF_EXISTS : STORE_YES;
	ulint	available_mem	= UNIV_PAGE_SIZE
		* (buf_pool_get_n_pages()
		   - (recv_n_pool_free_frames * srv_buf_pool_instances));

	end_lsn = *contiguous_lsn = ut_uint64_align_down(
		*contiguous_lsn, OS_FILE_LOG_BLOCK_SIZE);

	do {
   
		if (last_phase && store_to_hash == STORE_NO) {
   
			store_to_hash = STORE_IF_EXISTS;
			/* We must not allow change buffer
			merge here, because it would generate
			redo log records before we have
			finished the redo log scan. */
			recv_apply_hashed_log_recs(FALSE);
		}

		start_lsn = end_lsn;
		end_lsn += RECV_SCAN_SIZE;

		log_group_read_log_seg(
			log_sys->buf, group, start_lsn, end_lsn);
	} while (!recv_scan_log_recs(
			 available_mem, &store_to_hash, log_sys->buf,
			 RECV_SCAN_SIZE,
			 checkpoint_lsn,
			 start_lsn, contiguous_lsn, &group->scanned_lsn));

	if (recv_sys->found_corrupt_log || recv_sys->found_corrupt_fs) {
   
		DBUG_RETURN(false);
	}

	DBUG_PRINT("ib_log", ("%s " LSN_PF
			      " completed for log group " ULINTPF,
			      last_phase ? "rescan" : "scan",
			      group->scanned_lsn, group->id));

	DBUG_RETURN(store_to_hash == STORE_NO);
}

1、参数验证和初始化：

• 使用assert断言来确保如果last_phase为真，则必须有有效的检查点LSNrecv_sys->mlog_checkpoint_lsn。
• 初始化接收系统recv_sys的一些关键成员变量，比如长度、恢复偏移量、地址数量等，并清空哈希表。设置一些起始LSN比如srv_start_lsn、recv_sys->parse_start_lsn等为传入的contiguous_lsn值。

2、内存和资源准备：

• 计算可用的内存量，这是基于缓冲池的总页数减去为接收保留的空闲帧数。

3、日志扫描循环：

• 调整end_lsn为contiguous_lsn向下对齐到日志块大小OS_FILE_LOG_BLOCK_SIZE。

	end_lsn = *contiguous_lsn = ut_uint64_align_down(
		*contiguous_lsn, OS_FILE_LOG_BLOCK_SIZE);

• 在一个循环中，不断读取日志段log_group_read_log_seg，并处理日志记录recv_scan_log_recs。如果是在最后阶段且之前设置为不存储到哈希表STORE_NO，则更改为STORE_IF_EXISTS，并应用已哈希的日志记录。

	do {
   
		if (last_phase && store_to_hash == STORE_NO) {
   
            /* 如果满足条件，在日志解析中间，先进行日志应用操作
            如果日志缓冲区满，将更改store_to_hash策略为STORE_NO，且满足last_parse条件
            调用日志应用函数recv_apply_hashed_log_recs()*/
			store_to_hash = STORE_IF_EXISTS;
			recv_apply_hashed_log_recs(FALSE);
		}

		start_lsn = end_lsn;
		end_lsn += RECV_SCAN_SIZE;

		log_group_read_log_seg(
			log_sys->buf, group, start_lsn, end_lsn);  // 读取日志文件将start_lsn到end_lsn的日志读取到log_sys->buf

	} while (!recv_scan_log_recs(
			 available_mem, &store_to_hash, log_sys->buf,
			 RECV_SCAN_SIZE,
			 checkpoint_lsn,
			 start_lsn, contiguous_lsn, &group->scanned_lsn));  // while条件为日志解析函数入口

4、错误处理和返回：

• 如果在扫描过程中发现损坏的日志或文件系统，则返回false。
• 打印日志信息，表示扫描或重新扫描完成。
• 返回store_to_hash == STORE_NO的值，这可能表示是否还有更多日志需要处理。

2. recv_scan_log_recs()函数流程

static
bool
recv_scan_log_recs(   // 接收并扫描日志记录的函数
/*===============*/
	ulint		available_memory,/*!< in: we let the hash table of recs
					to grow to this size, at the maximum */
	store_t*	store_to_hash,	/*!< in,out: whether the records should be
					stored to the hash table; this is reset
					if just debug checking is needed, or
					when the available_memory runs out */
	const byte*	buf,		/*!< in: buffer containing a log
					segment or garbage */
	ulint		len,		/*!< in: buffer length */
	lsn_t		checkpoint_lsn,	/*!< in: latest checkpoint LSN */
	lsn_t		start_lsn,	/*!< in: buffer start lsn */
	lsn_t*		contiguous_lsn,	/*!< in/out: it is known that all log
					groups contain contiguous log data up
					to this lsn */
	lsn_t*		group_scanned_lsn)/*!< out: scanning succeeded up to
					this lsn */
{
   
	const byte*	log_block	= buf;
	ulint		no;
	lsn_t		scanned_lsn	= start_lsn;
	bool		finished	= false;
	ulint		data_len;
	bool		more_data	= false;
	ulint		recv_parsing_buf_size = RECV_PARSING_BUF_SIZE;

	ut_ad(start_lsn % OS_FILE_LOG_BLOCK_SIZE == 0);
	ut_ad(len % OS_FILE_LOG_BLOCK_SIZE == 0);
	ut_ad(len >= OS_FILE_LOG_BLOCK_SIZE);

	do {
   
		ut_ad(!finished);
		no = log_block_get_hdr_no(log_block);
		ulint expected_no = log_block_convert_lsn_to_no(scanned_lsn);
		if (no != expected_no) {
   
			finished = true;
			break;
		}

		if (!log_block_checksum_is_ok(log_block)) {
   
			ib::error() << "Log block " << no <<
				" at lsn " << scanned_lsn << " has valid"
				" header, but checksum field contains "
				<< log_block_get_checksum(log_block)
				<< ", should be "
				<< log_block_calc_checksum(log_block);
			finished = true;
			break;
		}

		if (log_block_get_flush_bit(log_block)) {
   

			if (scanned_lsn > *contiguous_lsn) {
   
				*contiguous_lsn = scanned_lsn;
			}
		}

		data_len = log_block_get_data_len(log_block);

		if (scanned_lsn + data_len > recv_sys->scanned_lsn
		    && log_block_get_checkpoint_no(log_block)
		    < recv_sys->scanned_checkpoint_no