MySQL redo log及recover过程浅析

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 */

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 };