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原作地址：http://www.cnblogs.com/liuhao/p/3714012.html
写在前面：作者水平有限，欢迎不吝赐教，一切以最新源码为准。
InnoDB redo log
669 /* Offsets of a log file header */ 670 #define LOG_GROUP_ID 0 /* log group number */ 671 #define LOG_FILE_START_LSN 4 /* lsn of the start of data in this 672 log file */ 673 #define LOG_FILE_NO 12 /* 4-byte archived log file number; 674 this field is only defined in an 675 archived log file */ 676 #define LOG_FILE_WAS_CREATED_BY_HOT_BACKUP 16 677 /* a 32-byte field which contains 678 the string ‘ibbackup‘ and the 679 creation time if the log file was 680 created by ibbackup --restore; 681 when mysqld is first time started 682 on the restored database, it can 683 print helpful info for the user */ 684 #define LOG_FILE_ARCH_COMPLETED OS_FILE_LOG_BLOCK_SIZE 685 /* this 4-byte field is TRUE when 686 the writing of an archived log file 687 has been completed; this field is 688 only defined in an archived log file */ 689 #define LOG_FILE_END_LSN (OS_FILE_LOG_BLOCK_SIZE + 4) 690 /* lsn where the archived log file 691 at least extends: actually the 692 archived log file may extend to a 693 later lsn, as long as it is within the 694 same log block as this lsn; this field 695 is defined only when an archived log 696 file has been completely written */ 697 #define LOG_CHECKPOINT_1 OS_FILE_LOG_BLOCK_SIZE 698 /* first checkpoint field in the log 699 header; we write alternately to the 700 checkpoint fields when we make new 701 checkpoints; this field is only defined 702 in the first log file of a log group */ 703 #define LOG_CHECKPOINT_2 (3 * OS_FILE_LOG_BLOCK_SIZE) 704 /* second checkpoint field in the log 705 header */ 706 #define LOG_FILE_HDR_SIZE (4 * OS_FILE_LOG_BLOCK_SIZE)
580 /* Offsets of a log block header */ 581 #define LOG_BLOCK_HDR_NO 0 /* block number which must be > 0 and 582 is allowed to wrap around at 2G; the 583 highest bit is set to 1 if this is the 584 first log block in a log flush write 585 segment */ 586 #define LOG_BLOCK_FLUSH_BIT_MASK 0x80000000UL 587 /* mask used to get the highest bit in 588 the preceding field */ 589 #define LOG_BLOCK_HDR_DATA_LEN 4 /* number of bytes of log written to 590 this block */ 591 #define LOG_BLOCK_FIRST_REC_GROUP 6 /* offset of the first start of an 592 mtr log record group in this log block, 593 0 if none; if the value is the same 594 as LOG_BLOCK_HDR_DATA_LEN, it means 595 that the first rec group has not yet 596 been catenated to this log block, but 597 if it will, it will start at this 598 offset; an archive recovery can 599 start parsing the log records starting 600 from this offset in this log block, 601 if value not 0 */ 602 #define LOG_BLOCK_CHECKPOINT_NO 8 /* 4 lower bytes of the value of 603 log_sys->next_checkpoint_no when the 604 log block was last written to: if the 605 block has not yet been written full, 606 this value is only updated before a 607 log buffer flush */ 608 #define LOG_BLOCK_HDR_SIZE 12 /* size of the log block header in 609 bytes */ 610 611 /* Offsets of a log block trailer from the end of the block */ 612 #define LOG_BLOCK_CHECKSUM 4 /* 4 byte checksum of the log block 613 contents; in InnoDB versions 614 < 3.23.52 this did not contain the 615 checksum but the same value as 616 .._HDR_NO */ 617 #define LOG_BLOCK_TRL_SIZE 4 /* trailer size in bytes */
| log_sys->lsn | 接下来将要生成的log record使用此lsn的值 |
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log_sys->flushed_do_disk_lsn
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redo log file已经被刷新到此lsn。比该lsn值小的日志记录已经被安全的记录在磁盘上 |
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log_sys->write_lsn
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当前正在执行的写操作使用的临界lsn值； |
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log_sys->current_flush_lsn
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当前正在执行的write + flush操作使用的临界lsn值，一般和log_sys->write_lsn相等； |
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log_sys->buf
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内存中全局的log buffer，和每个mtr自己的buffer有所区别；
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log_sys->buf_size
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log_sys->buf的size
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log_sys->buf_free
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写入buffer的起始偏移量
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log_sys->buf_next_to_write
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buffer中还未写到log file的起始偏移量。下次执行write+flush操作时，将会从此偏移量开始
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log_sys->max_buf_free
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确定flush操作执行的时间点，当log_sys->buf_free比此值大时需要执行flush操作，具体看log_check_margins函数
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376 /* Mini-transaction handle and buffer */
377 struct mtr_t{
378 #ifdef UNIV_DEBUG
379 ulint state; /*!< MTR_ACTIVE, MTR_COMMITTING, MTR_COMMITTED */
380 #endif
381 dyn_array_t memo; /*!< memo stack for locks etc. */
382 dyn_array_t log; /*!< mini-transaction log */
383 unsigned inside_ibuf:1;
384 /*!< TRUE if inside ibuf changes */
385 unsigned modifications:1;
386 /*!< TRUE if the mini-transaction
387 modified buffer pool pages */
388 unsigned made_dirty:1;
389 /*!< TRUE if mtr has made at least
390 one buffer pool page dirty */
391 ulint n_log_recs;
392 /* count of how many page initial log records
393 have been written to the mtr log */
394 ulint n_freed_pages;
395 /* number of pages that have been freed in
396 this mini-transaction */
397 ulint log_mode; /* specifies which operations should be
398 logged; default value MTR_LOG_ALL */
399 lsn_t start_lsn;/* start lsn of the possible log entry for
400 this mtr */
401 lsn_t end_lsn;/* end lsn of the possible log entry for
402 this mtr */
403 #ifdef UNIV_DEBUG
404 ulint magic_n;
405 #endif /* UNIV_DEBUG */
406 };
(trx_commit_in_memory() / trx_commit_complete_for_mysql() / trx_prepare() e.t.c)-> trx_flush_log_if_needed()-> trx_flush_log_if_needed_low()-> log_write_up_to()-> log_group_write_buf().
srv_master_thread()-> (srv_master_do_active_tasks() / srv_master_do_idle_tasks() / srv_master_do_shutdown_tasks())-> srv_sync_log_buffer_in_background()-> log_buffer_sync_in_background()->log_write_up_to()->... .
146 /** Wrapper for recv_recovery_from_checkpoint_start_func(). 147 Recovers from a checkpoint. When this function returns, the database is able 148 to start processing of new user transactions, but the function 149 recv_recovery_from_checkpoint_finish should be called later to complete 150 the recovery and free the resources used in it. 151 @param type in: LOG_CHECKPOINT or LOG_ARCHIVE 152 @param lim in: recover up to this log sequence number if possible 153 @param min in: minimum flushed log sequence number from data files 154 @param max in: maximum flushed log sequence number from data files 155 @return error code or DB_SUCCESS */ 156 # define recv_recovery_from_checkpoint_start(type,lim,min,max) 157 recv_recovery_from_checkpoint_start_func(type,lim,min,max)
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recv_sys->limit_lsn
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恢复应该执行到的最大的LSN值，这里赋值为LSN_MAX（uint64_t的最大值） |
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recv_sys->parse_start_lsn
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恢复解析日志阶段所使用的最起始的LSN值，这里等于最后一次执行checkpoint对应的LSN值 |
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recv_sys->scanned_lsn
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当前扫描到的LSN值 |
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recv_sys->recovered_lsn
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当前恢复到的LSN值，此值小于等于recv_sys->scanned_lsn |
2908 /*******************************************************//**
2909 Scans log from a buffer and stores new log data to the parsing buffer. Parses
2910 and hashes the log records if new data found. */
2911 static
2912 void
2913 recv_group_scan_log_recs(
2914 /*=====================*/
2915 log_group_t* group, /*!< in: log group */
2916 lsn_t* contiguous_lsn, /*!< in/out: it is known that all log
2917 groups contain contiguous log data up
2918 to this lsn */
2919 lsn_t* group_scanned_lsn)/*!< out: scanning succeeded up to
2920 this lsn */
2930 while (!finished) {
2931 end_lsn = start_lsn + RECV_SCAN_SIZE;
2932
2933 log_group_read_log_seg(LOG_RECOVER, log_sys->buf,
2934 group, start_lsn, end_lsn);
2935
2936 finished = recv_scan_log_recs(
2937 (buf_pool_get_n_pages()
2938 - (recv_n_pool_free_frames * srv_buf_pool_instances))
2939 * UNIV_PAGE_SIZE,
2940 TRUE, log_sys->buf, RECV_SCAN_SIZE,
2941 start_lsn, contiguous_lsn, group_scanned_lsn);
2942 start_lsn = end_lsn;
2943 }
105 /** Wrapper for recv_recover_page_func(). 106 Applies the hashed log records to the page, if the page lsn is less than the 107 lsn of a log record. This can be called when a buffer page has just been 108 read in, or also for a page already in the buffer pool. 109 @param jri in: TRUE if just read in (the i/o handler calls this for 110 a freshly read page) 111 @param block in/out: the buffer block 112 */ 113 # define recv_recover_page(jri, block) recv_recover_page_func(jri, block)
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原文地址：http://www.cnblogs.com/jiweixiao/p/4454150.html
