Understanding of InnoDB Redo Buffer

A discussion on the structure of InnoDB redo (1@ tomorrow will be better (Group No.: 196380905)1. Redo log: The structure of the Redo log is physical to the page, logical to the record, and the physical logical log is used. InnoDB redo logs are based on mini-implemented by transaction. Each redo log block is 512 bytes, which means that the log buffer is also organized as a 512-byte block. Each mini-transaction will have a structure of MTR, the structure of this MTR encapsulates a log not written to the log buffer, the MTR structure has a log member, the member is the structure of the log.            Log_t is the structure that represents the log buffer, and only one Sys_log instance (lot_t sys_log) is maintained in the mysqld running instance. Sys_log maintained the size of the innodb_log_buffer_size developed by US redo buffer. The memory area in the Sys_log-BUF maintains this area of memory. Redo Buffer has the following three structures:|----------------|  |                Block Header |                |----------------|  |                Records Logs |                |----------------|  |                         Block Trialer | |----------------|(log block structure)|----------|----------|----------|----------|         |log Block |log Block |log block |log block | |----------|----------|----------|----------|(log buffer organization) the header and tail in the log buffer are defined in the source code:/*offsets of a log block header*/        #defineLog_block_hdr_no 0/* BLOCK number which must be > 0 and isallowed to wrap around at 2G; the highest bit is SetTo1 if  This  isThe first log blockincha log flush write segment*/#defineLog_block_flush_bit_mask 0x80000000ul/*mask used to get the highest bit in the preceding field*/        #defineLog_block_hdr_data_len 4/* Number of bytes of log written to ThisBlock */#defineLog_block_first_rec_group 6/* Offset of the first start of anMTR Log Record Groupinch  Thislog block,0 ifNoneifThe value isThe same asLog_block_hdr_data_len, it means that the first REC group have not yet been Cate Nated to Thislog block, butifIt'll, it'll start at Thisoffset; An archive recovery can start parsing the log records starting  from  ThisOffsetinch  Thislog block,ifValue not0*/#defineLog_block_checkpoint_no 8/* 4 Lower bytes of the value ofLog_sys-Next_checkpoint_no when the log block is last written to:ifThe block has no yet been written full, ThisValue isOnly updated before a log buffer flush*/#defineLog_block_hdr_size/* SIZE of the log BLOCK header inbytes*//*offsets of a log block trailer from the end of the block*/        #defineLog_block_checksum 4/* 4 byte CHECKSUM of the log BLOCKcontents;inchInnoDB versions<3.23. the  ThisDid not contain the checksum but the same value as                    .. _hdr_no*/#defineLog_block_trl_size 4/* Trailer SIZE in bytes */Mini-transactions is the abbreviation for MTR, which centralizes a set of log record and writes it to log buffer. /*mini-transaction handle and buffer*/            structmtr_t{#ifdef univ_debug ulint State; /*!< mtr_active, mtr_committing, mtr_committed*/            #endifdyn_array_t Memo; /*!< Memo stack for locks etc.*/dyn_array_t log; /*!< mini-transaction Log*/unsigned inside_ibuf:1; /*!< TRUE If inside ibuf changes*/unsigned modifications:1; /*!< TRUE If the mini-transaction modified buffer pool pages*/unsigned made_dirty:1; /*!< TRUE If MTR have made at least one buffer pool page dirty*/Ulint n_log_recs; /*count of how many page initial log records has been written to the MTR log*/Ulint n_freed_pages; /*Number of pages that has been freed in this mini-transaction*/Ulint Log_mode;/*specifies which operations should be logged; default value Mtr_log_all*/lsn_t start_lsn;/*start LSN of the possible log entry for this MTR*/lsn_t end_lsn;/*end LSN of the possible log entry for this MTR*/#ifdef univ_debug ulint magic_n; #endif/* Univ_debug */            }; Definition of dyn_block_t:/** A block in a dynamically allocated array*/            structdyn_block_t; /** Dynamically allocated array*/typedef dyn_block_t dyn_array_t; /** This is the initial ' payload ' size of a dynamic array; This must is > Mlog_buf_margin + 30! */            #defineDyn_array_data_size 512/*#################################################################*/            /** @brief a block in a dynamically allocated array. note! Do not access the fields of the struct directly:the definition appears this compiler to know its size! */            structdyn_block_t{mem_heap_t* HEAP;/*!< in the first block this is! = NULL If dynamic allocation has been needed*/Ulint used; /*!< number of data bytes used in this block; Dyn_block_full_flag is set when the BLOCK becomes*/                byteData[dyn_array_data_size];//real-World log data                            /*!< storage for array elements*/ut_list_base_node_t (dyn_block_t)Base; /*!< Linear list of dyn blocks:this node is used only in the first block*/ut_list_node_t (dyn_block_t) LIST; /*!< Linear list node:used in all blocks*/#ifdef univ_debug ulint buf_end;/*!< only in the debug version:if dyn array are opened, this is the buffer End offset, else this is 0*/Ulint magic_n;/*!< Magic Number (Dyn_block_magic_n)*/            #endif            };2. mini-logic for calling methods of transaction log: Mtr_commit-Mtr_log_reserve_and_write->log_write_low//the function is to write the Mtr->log to the free log buffer.        /************************************************************//** Writes the contents of a mini-transaction log, if any, to the database log.*/        Static voidMtr_log_reserve_and_write (mtr_t* mtr)/*!< in/out:mtr*/--->/************************************************************//** Writes to the log the string given. It is assumed that the caller holds the log mutex. */Univ_internvoidLog_write_low (byte* STR/*!< in:string*/, Ulint Str_len/*!< in:string Length*/)

Understanding of InnoDB Redo Buffer