{"id":10005999,"date":"2022-07-22T19:36:56","date_gmt":"2022-07-22T11:36:56","guid":{"rendered":"https:\/\/ityet.com\/?p=10005999"},"modified":"2022-07-22T19:36:56","modified_gmt":"2022-07-22T11:36:56","slug":"innodb%e4%b9%8bundo-log%e4%bb%8b%e7%bb%8d","status":"publish","type":"post","link":"https:\/\/itmax.cn\/?p=10005999","title":{"rendered":"InnoDB\u4e4bUNDO LOG\u4ecb\u7ecd"},"content":{"rendered":"<p>\u7b80\u4ecb\uff1a\u00a0undo log\u662fInnoDB\u4e8b\u52a1\u7279\u6027\u7684\u91cd\u8981\u7ec4\u6210\u90e8\u5206\u3002\u5f53\u5bf9\u8bb0\u5f55\u505a\u589e\u5220\u6539\u64cd\u4f5c\u5c31\u4f1a\u4ea7\u751fundo\u8bb0\u5f55\uff0cundo\u8bb0\u5f55\u4f1a\u8bb0\u5f55\u5230\u5355\u72ec\u7684\u8868\u7a7a\u95f4\u4e2d\u3002 \u672c\u6587\u5c06\u4ece\u4ee3\u7801\u5c42\u9762\u5bf9undo log\u8fdb\u884c\u4e00\u4e2a\u7b80\u5355\u7684\u4ecb\u7ecd\uff1b\u4e3b\u8981\u4ece\u4e0b\u9762\u56db\u4e2a\u65b9\u9762\u6765\u4ecb\u7ecdundo log\uff1aundo log\u7ec4\u7ec7\u5f62\u5f0f\u4e0e\u5206\u914d\u4e0e\u8bb0\u5f55\uff0c\u4ee5\u53caundo log\u7684\u5e94\u7528\u53ca\u5176\u6e05\u7406\u3002\u4ece\u8fd9\u56db\u4e2a\u65b9\u9762\u51fa\u53d1\uff0c\u6211\u4eec\u5c31\u53ef\u4ee5\u57fa\u672c\u4e86\u89e3undo log\u7684\u6574\u4e2a\u751f\u547d\u5468\u671f\u3002\u672c\u6587\u57fa\u4e8eMySQL Community 8.0.23 Version \u00a0undo log\u7684\u7ec4\u7ec7\u5f62\u5f0f\u6b64\u90e8\u5206\u662f\u5173\u4e8eUndo log\u7684\u7ec4\u7ec7\u5f62\u5f0f\u7684\u4e00\u4e2a\u4ecb\u7ecd\uff1b\u4e3b\u8981\u5206\u4e3a\u4e24\u90e8\u5206\u6765\u5bf9undo log\u7684\u7ec4\u7ec7\u5f62\u5f0f\u8fdb\u884c\u4ecb\u7ecd\uff1a\u6587\u4ef6\u7ed3\u6784\u548c\u5185\u5b58\u7ed3\u6784\u3002\u5728\u4ecb\u7ecd\u8fd9\u4e24\u90e8\u5206\u65f6\uff0c\u5148\u4ece\u5c40\u90e8\u51fa\u53d1\uff0c\u6700\u540e\u518d\u7ed9\u51fa\u5404\u4e2a\u90e8\u5206\u7684\u8054\u7cfb\u30021. \u6587\u4ef6\u7ed3\u6784\u9996\u5148\uff0c\u5728MySQL5.6\u4e4b\u524d\u6240\u6709\u7684undo log\u5168\u90e8\u5b58\u50a8\u5728\u7cfb\u7edf\u8868\u7a7a\u95f4\u4e2d(ibdata1)\uff1b\u4f46\u662f\u4ece5.6\u5f00\u59cb\u4e5f\u53ef\u4ee5\u4f7f\u7528\u72ec\u7acb\u8868\u7a7a\u95f4\u6765\u5b58\u50a8undo log\u3002\u5f53\u524d\u7248\u672cInnoDB\u9ed8\u8ba4\u6709\u4e24\u4e2aundo tablespace\uff0c\u4e5f\u53ef\u4ee5\u4f7f\u7528CREATE UNDO TABLESPACE\u8bed\u53e5\u52a8\u6001\u6dfb\u52a0\uff0c\u6700\u5927128\u4e2a\uff1b\u6bcf\u4e2aundo tablespace\u81f3\u591a\u53ef\u4ee5\u6709TRX_SYS_N_RSEGS(128)\u4e2a\u56de\u6eda\u6bb5\u30021.1 Rollback Segment(\u56de\u6eda\u6bb5)InnoDB\u5728undo tablespace\u4e2d\u4f7f\u7528\u56de\u6eda\u6bb5\u6765\u7ec4\u7ec7undo log\u3002\u540c\u65f6\u4e3a\u4e86\u4fdd\u8bc1\u4e8b\u52a1\u7684\u5e76\u53d1\u64cd\u4f5c\uff0c\u5728\u5199undo log\u65f6\u4e0d\u4ea7\u751f\u51b2\u7a81\uff0cInnoDB\u4f7f\u7528 \u56de\u6eda\u6bb5 \u6765\u7ef4\u62a4undo log\u7684\u5e76\u53d1\u5199\u5165\u548c\u6301\u4e45\u5316\uff1b\u800c\u6bcf\u4e2a\u56de\u6eda\u6bb5 \u53c8\u6709\u591a\u4e2aundo log slot\u3002\u901a\u5e38\u901a\u8fc7Rollback Segment Header\u6765\u7ba1\u7406\u56de\u6eda\u6bb5\uff0cRollback Segment Header\u901a\u5e38\u5728\u56de\u6eda\u6bb5\u7684\u7b2c\u4e00\u4e2a\u9875\uff0c\u5177\u4f53\u7ed3\u6784\u5982\u4e0b\uff1a<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209803\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0\u00a0Max Size\uff1a\u53c2\u6570\u540d\u4e3a TRX_RSEG_MAX_SIZE\uff0c\u56de\u6eda\u6bb5\u53ef\u4ee5\u6709\u7528\u7684\u6700\u5927page\u6570\u3002History Size\uff1a\u53c2\u6570\u540d\u4e3aTRX_RSEG_HISTORY_SIZE\uff0chistory list\u5305\u542b\u7684page\u6570\u3002History List Base Node\uff1a\u53c2\u6570\u540d\u4e3aTRX_RSEG_HISTORY\uff0chistory list\u7684Base Node\u3002Rollback Segment FSEG Entry\uff1a\u53c2\u6570\u540d\u4e3aTRX_RSEG_FSEG_HEADER\uff0cfile segment\u7684\u5b58\u653e\u4f4d\u7f6e\u3002Undo Slots Dictionary\uff1a\u53c2\u6570\u540d\u4e3aTRX_RSEG_UNDO_SLOTS\uff0c\u5b58\u653e\u6d3b\u8dc3\u4e8b\u52a1\u7684undo header page no\u3002Rollback Segment Header\u91cc\u9762\u6700\u91cd\u8981\u7684\u4e24\u90e8\u5206\u5c31\u662fhistory list\u4e0eundo slot directory\u3002\u5176\u4e2dhistory list\u628a\u6240\u6709\u5df2\u7ecf\u63d0\u4ea4\u4f46\u8fd8\u6ca1\u6709\u88abpurge\u4e8b\u52a1\u7684undo log\u4e32\u8054\u8d77\u6765\uff0cpurge\u7ebf\u7a0b\u53ef\u4ee5\u901a\u8fc7\u6b64list\u5bf9\u6ca1\u6709\u4e8b\u52a1\u4f7f\u7528\u7684undo log\u8fdb\u884cpurge\u3002\u6bcf\u4e2a\u4e8b\u52a1\u5728\u9700\u8981\u8bb0\u5f55undo log\u65f6\u90fd\u4f1a\u7533\u8bf7\u4e00\u4e2a\u6216\u4e24\u4e2aslot(insert\/update\u5206\u5f00)\uff0c\u540c\u65f6\u628a\u4e8b\u52a1\u7684\u7b2c\u4e00\u4e2aundo page\u653e\u5165\u5bf9\u5e94slot\u4e2d\uff1b\u6240\u4ee5\u7406\u8bba\u4e0aInnoDB\u5141\u8bb8\u7684\u6700\u5927\u4e8b\u52a1\u5e76\u53d1\u6570\u4e3a128(undo tablespace) <em> 128(Rollback Segment) <\/em> 1024(TRX_RSEG_UNDO_SLOTS)\u3002\u4e0b\u9762\u6211\u4eec\u8fdb\u4e00\u6b65\u4ecb\u7ecdundo log\u5728\u78c1\u76d8\u4e0a\u5982\u4f55\u8bb0\u5f55\u30021.2 UndoPage\u8981\u60f3\u77e5\u9053undo log\u5982\u4f55\u8bb0\u5f55\uff0c\u6211\u4eec\u5148\u8981\u641e\u6e05\u695a\u4e00\u4e2aundo page\u5177\u4f53\u5185\u5bb9\uff0cundo page\u4e00\u822c\u5206\u4e24\u79cd\u60c5\u51b5\uff1aheader page\u548cnormal page \u3002header page\u9664\u4e86normal page\u6240\u5305\u542b\u7684\u4fe1\u606f\uff0c\u8fd8\u5305\u542b\u4e00\u4e9bundo segment\u4fe1\u606f\uff0c\u540e\u9762\u4f1a\u5bf9undo segment\u8fdb\u884c\u8be6\u7ec6\u4ecb\u7ecd\u3002\u6211\u4eec\u4e0b\u9762\u5148\u4ecb\u7ecd\u4e00\u4e0bundo header page\u7684\u8be6\u7ec6\u5206\u5e03\u3002<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209804\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0\u00a0undo header page\u662f\u4e8b\u52a1\u9700\u8981\u5199undo log\u65f6\u7533\u8bf7\u7684\u7b2c\u4e00\u4e2aundo page\uff1b\u4e00\u4e2aundo header page\u4ed6\u540c\u4e00\u65f6\u523b\u53ea\u96b6\u5c5e\u4e8e\u540c\u4e00\u4e2a\u6d3b\u8dc3\u4e8b\u52a1\uff0c\u4f46\u662f\u4e00\u4e2aundo header page\u4e0a\u9762\u7684\u5185\u5bb9\u53ef\u80fd\u5305\u542b\u591a\u4e2a\u5df2\u7ecf\u63d0\u4ea4\u7684\u4e8b\u52a1\u548c\u4e00\u4e2a\u6d3b\u8dc3\u4e8b\u52a1\u3002undo normal page\u662f\u5f53\u6d3b\u8dc3\u4e8b\u52a1\u4ea7\u751f\u7684undo record\u8d85\u8fc7undo header page\u5bb9\u91cf\u540e\uff0c\u5355\u72ec\u518d\u4e3a\u6b64\u4e8b\u52a1\u5206\u914d\u7684undo page(\u53c2\u8003\u51fd\u6570trx_undo_add_page)\uff1b\u6b64page\u53ea\u96b6\u5c5e\u4e8e\u4e00\u4e2a\u4e8b\u52a1\uff0c\u53ea\u5305\u542bundo page header\u4e0d\u5305\u542bundo segment header\u30021.3 Undo Page Header\u6bcf\u4e00\u4e2aundo page\u90fd\u8981\u6709header\uff0c\u5176\u4e2d\u8bb0\u5f55\u4e86\u5f53\u524dundo page\u7684\u4e00\u4e9b\u72b6\u6001\u4fe1\u606f\uff0c\u5177\u4f53\u5185\u5bb9\u5982\u4e0b\uff1a<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209805\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0\u00a0Undo Page Type\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_PAGE_TYPE\uff0c\u4f7f\u7528\u8be5page\u4e8b\u52a1\u7684\u7c7b\u578b\uff0c\u5305\u542bTRX_UNDO_INSERT\uff0cTRX_UNDO_UPDATE\u4e24\u79cd\u3002Latest Log Record Offset\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_PAGE_START\uff0c\u6700\u65b0\u4e8b\u52a1\u5f00\u59cb\u8bb0\u5f55undo log\u8d77\u59cb\u4f4d\u7f6e\u3002Free Space Offset\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_PAGE_FREE\uff0c\u9875\u5185\u7a7a\u95f2\u7a7a\u95f4\u8d77\u59cb\u5730\u5740\uff0c\u5728\u6b64\u4e4b\u540e\u53ef\u8bb0\u5f55undo log\u3002Undo Page List Node\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_PAGE_NODE\uff0cundo page list\u8282\u70b9\uff0c\u53ef\u4ee5\u628a\u540c\u4e00\u4e2a\u4e8b\u52a1\u6240\u7528\u5230\u7684\u6240\u6709undo page\u53cc\u5411\u4e32\u8054\u8d77\u6765\u30021.4 Undo Segment Header<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209806\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0\u00a0State\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_STATE\uff0cundo segment\u7684\u72b6\u6001\uff0cTRX_UNDO_ACTIVE\u7b49Last Log Offset\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_LAST_LOG\uff0c\u5f53\u524dpage\u6700\u540e\u4e00\u4e2aundo log header\u7684\u4f4d\u7f6e\u3002Undo Segment FSEG Entry\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_FSEG_HEADER\uff0csegment\u5bf9\u5e94\u7684inode\u7684\uff08space_id\uff0cpage_no\uff0coffset\u7b49\uff09Undo Segment Page List Base Node\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_PAGE_LIST\uff0cundo page list\u7684Base Node\uff0c\u5bf9\u4e8e\u540c\u4e00\u4e2a\u4e8b\u52a1\u4e0b\u7684undo header page\u548cundo normal page\u6784\u6210\u53cc\u5411\u94fe\u8868\u3002\u4e0a\u9762\u53ea\u662f\u4ecb\u7ecd\u4e86\u4e00\u4e9bundo log\u5728\u6587\u4ef6\u4e0a\u7684\u57fa\u672c\u7ed3\u6784\uff0c\u4e0b\u9762\u6211\u4eec\u7ee7\u7eed\u4ecb\u7ecd\u8bb0\u5f55undo log\u65f6\u7684\u6587\u4ef6\u7ec4\u7ec7\u30021.5 Undo Log Header\u5f53\u4e8b\u52a1\u5f00\u59cb\u8bb0\u5f55undo log\u65f6\uff0c\u5148\u521b\u5efa\u4e00\u4e2aundo log header\uff0c\u5f53update\/delete\u4e8b\u52a1\u7ed3\u675f\u540e\uff0cundo log header\u5c06\u4f1a\u88ab\u52a0\u5165\u5230hisotry list\u4e2d\uff1binsert\u4e8b\u52a1\u7684undo log\u4f1a\u88ab\u7acb\u5373\u91ca\u653e\u3002<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209807\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0\u00a0Transaction ID\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_TRX_ID\uff0c\u4e8b\u52a1id\uff08\u4e8b\u52a1\u5f00\u59cb\u7684\u903b\u8f91\u65f6\u95f4\uff09Transaction Number\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_TRX_NO\uff0c\u4e8b\u52a1no\uff08\u4e8b\u52a1\u7ed3\u675f\u7684\u903b\u8f91\u65f6\u95f4\uff09Delete Marks Flags\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_DEL_MARKS\uff0c\u5982\u679c\u6d89\u53ca\u5230\u5220\u9664\u8bb0\u5f55\u4e3aTRUELog Start Offset\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_LOG_START\uff0c\u4e8b\u52a1\u4e2d\u7b2c\u4e00\u4e2aundo record\u5730\u5740\u3002XID Flag\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_XID_EXISTS\uff0c\u7528\u4e8eXID\u3002DDL Transaction Flag\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_DICT_TRANS\uff0c\u662f\u5426\u662fDDL\u4e8b\u52a1Table ID if DDL Transaction\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_TABLE_ID\uff0c\u5982\u679c\u662fDDL\u4e8b\u52a1\uff0c\u8bb0\u5f55table id\u3002Next Undo Log Offset\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_NEXT_LOG\uff0c\u5f53\u524d\u9875\u7684\u4e0b\u4e00\u4e2aundo log header\u4f4d\u7f6ePrev Undo Log Offset\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_PREV_LOG\uff0c\u5f53\u524d\u9875\u7684\u4e0a\u4e00\u4e2aundo log header\u4f4d\u7f6eHistory List Node\uff1a\u53c2\u6570\u540d\u4e3aTRX_UNDO_HISTORY_NODE\uff0c\u4e8b\u52a1\u7ed3\u675f\u65f6\u653e\u5165history list\u7684\u8282\u70b9\u3002\u6709\u5173XID\u7684\u5185\u5bb9\u6682\u65f6\u4e0d\u4ecb\u7ecd\u3002\u6709\u4e86undo log header\u540e\uff0c\u6211\u4eec\u5c31\u53ef\u4ee5\u8bb0\u5f55undo record\u4e86\u30021.6 Undo Record<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209808\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0\u00a0Previous Record Offset\uff1a\u5b58\u50a8\u4e0a\u4e00\u6761record\u7684\u4f4d\u7f6e\u3002Next Record Offset\uff1a\u5b58\u50a8\u4e0b\u4e00\u6761record\u7684\u4f4d\u7f6e\u3002Type + Extern Flag + Compilation Info\uff1a\u5b58undo record\u7684type\u7b49\u4fe1\u606f\u3002\u53ef\u4ee5\u4ece\u4e0a\u9762\u56fe\u4e2d\u770b\u51fa\uff0cundo record\u9664\u4e86\u5b58\u50a8\u8fd9\u91cc\u6bd4\u8f83\u91cd\u8981\u7684\u51e0\u4e2a\u4fe1\u606f\uff0c\u5305\u542b\u524d\u540eundo record\u4f4d\u7f6e\uff0c\u7c7b\u578b\uff0cundo no\uff0ctable id\u7b49\uff1b\u800cundo recod\u4e2d\u5177\u4f53\u5b58\u50a8\u7684\u5185\u5bb9\u6211\u4eec\u7b49\u5230\u300aundo log\u7684\u5206\u914d\u4e0e\u8bb0\u5f55\u300b\u4e2d\u53bb\u4ecb\u7ecd\u3002\u6700\u540e\uff0c\u6211\u4eec\u901a\u8fc7\u4e0b\u9762\u8fd9\u5e45\u56fe\u6765\u4e86\u89e3undo log\u5728\u6587\u4ef6\u7ec4\u7ec7\u4e0a\u7684\u4e00\u4e2a\u603b\u89c8\u3002<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209809\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0\u00a02. \u4e3b\u8981\u5185\u5b58\u6570\u636e\u7ed3\u6784\u4e3a\u4e86\u65b9\u4fbf\u7ba1\u7406\u548c\u8bb0\u5f55undo log\uff0c\u5728\u5185\u5b58\u4e2d\u6709\u5982\u4e0b\u5173\u952e\u7ed3\u6784\u4f53\u5bf9\u8c61\uff1aundo::Tablespace\uff1aundo tablespace\u5185\u5b58\u7ed3\u6784\u4f53\uff0c\u7ef4\u62a4undo tablespace\u76f8\u5173\u4fe1\u606f\uff0c\u7ba1\u7406\u6b64tablespace\u4e2d\u76f8\u5173\u56de\u6eda\u6bb5\u3002trx_rseg_t\uff1a\u56de\u6eda\u6bb5\u7684\u5185\u5b58\u7ed3\u6784\u4f53\uff0c\u7528\u4e8e\u7ef4\u62a4\u56de\u6eda\u6bb5\u76f8\u5173\u4fe1\u606f\u3002trx_undo_t\uff1aundo log\u5185\u5b58\u7ed3\u6784\u4f53\uff0c\u7528\u4e8e\u7ef4\u62a4undo log type\u7b49\u4fe1\u606f\uff0c\u4fbf\u4e8e\u5bf9undo page\u8fdb\u884c\u7ef4\u62a4\u548c\u7ba1\u7406\u3002purge_pq_t\uff1apurge queue\uff0c\u5bf9\u5df2\u7ecf\u63d0\u4ea4\u4e8b\u52a1\u7684undo log\u8fdb\u884c\u7ef4\u62a4\u548c\u56de\u6536\u3002trx_t\uff1a\u4e8b\u52a1\u7684\u5185\u5b58\u7ed3\u6784\u4f53\uff0c\u5bf9\u4e8b\u52a1\u7684\u4fe1\u606f\u8fdb\u884c\u7ba1\u7406\u548c\u7ef4\u62a4\u3002\u6211\u4eec\u91cd\u70b9\u5bf9trx_rseg_t\u7ed3\u6784\u4f53\u7684\u5185\u5bb9\u8fdb\u884c\u4ecb\u7ecd\u3002trx_rseg_t\u4e3b\u8981\u6570\u636e\u6210\u5458\uff1alast_page_no\uff1ahistory list\u4e0a\u6b64rseg\u6700\u540e\u4e00\u4e2a\u6ca1\u6709\u88abpurge\u7684page no\u3002last offset\uff1a\u6700\u540e\u4e00\u4e2a\u672a\u88abpurge\u7684undo log header \u504f\u79fb\u3002last trx no\uff1a\u6700\u540e\u4e00\u4e2a\u672a\u88abpurge\u7684\u4e8b\u52a1no\u3002last_del_marks\uff1a\u6700\u540e\u4e00\u4e2a\u672a\u88abpurge\u7684\u65e5\u5fd7\u9700\u8981\u88ab\u6e05\u7406\u3002\u4e0a\u9762\u56db\u4e2a\u6570\u636e\u53ef\u4ee5\u4ecetrx_undo_t\u4e2d\u83b7\u53d6\uff0c\u53c2\u8003trx_purge_add_update_undo_to_history\u51fd\u6570\u3002trx_ref_count\uff1a\u88ab\u6d3b\u8dc3\u4e8b\u52a1\u5f15\u7528\u7684\u8ba1\u6570\u5668\uff1b\u975e0\u65f6\uff0c\u6b64\u56de\u6eda\u6bb5\u6240\u5728\u7684tablespace\u4e0d\u53ef\u4ee5\u88abtruncate\u3002update_undo_list\uff1a\u6240\u6709\u6d3b\u8dc3\u7684update\u4e8b\u52a1\u7684trx_undo_t\u5bf9\u8c61\u5b58\u50a8\u5728\u6b64\u94fe\u8868\u3002update_undo_cached\uff1a\u5982\u679cupdate\u4e8b\u52a1\u63d0\u4ea4\u65f6\uff0c\u6b64\u4e8b\u52a1\u53ea\u4f7f\u7528\u4e86\u4e00\u4e2apage\u5e76\u4e14\u6b64page\u5269\u4f59\u7a7a\u95f4\u5927\u4e8e1\/4\u653e\u5165\u6b64\u94fe\u8868\uff1b\u65b0update\u4e8b\u52a1\u65b0\u7533\u8bf7undo log\u65f6\u4f18\u5148\u4ece\u6b64\u94fe\u8868\u5206\u914d\u3002insert_undo_list\uff1a\u6240\u6709\u6d3b\u8dc3\u7684insert\u4e8b\u52a1\u7684trx_undo_t\u5bf9\u8c61\u5b58\u50a8\u5728\u6b64\u94fe\u8868\u3002insert_undo_cached\uff1a\u5982\u679cinsert\u4e8b\u52a1\u63d0\u4ea4\u65f6\uff0c\u6b64\u4e8b\u52a1\u53ea\u4f7f\u7528\u4e86\u4e00\u4e2apage\u5e76\u4e14\u6b64page\u5269\u4f59\u7a7a\u95f4\u5927\u4e8e1\/4\u653e\u5165\u6b64\u94fe\u8868\uff1b\u65b0insert\u4e8b\u52a1\u65b0\u7533\u8bf7undo log\u65f6\u4f18\u5148\u4ece\u6b64\u94fe\u8868\u5206\u914d\u3002\u4e0b\u9762\u6211\u4eec\u901a\u8fc7\u4e00\u526f\u5173\u7cfb\u56fe\u6765\u4ecb\u7ecd\u5185\u5b58\u4e2d\u5404\u4e2a\u5173\u952e\u7ed3\u6784\u4f53\u4e4b\u95f4\u7684\u5173\u7cfb\uff1b\u5176\u4e2d\u5b9e\u7ebf\u4ee3\u8868\u62e5\u6709\u8be5\u5bf9\u8c61\uff0c\u865a\u7ebf\u4ee3\u8868\u5f15\u7528\u8be5\u5bf9\u8c61\u3002<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209810\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0\u00a0undo log\u7684\u5206\u914d\u4e0e\u8bb0\u5f55\u6211\u4eec\u901a\u8fc7\u4e4b\u524d\u7684\u4ecb\u7ecd\u4e86\u89e3\u5230\uff1bundo log\u5728\u78c1\u76d8\u548c\u5185\u5b58\u4e2d\u662f\u5982\u4f55\u7ec4\u7ec7\u7684\uff1b\u4ece\u4e2d\u4e86\u89e3\u5230\uff0c\u56de\u6eda\u6bb5\u4e0d\u8bba\u5728\u78c1\u76d8\u548c\u5185\u5b58\u4e2d\uff0c\u90fd\u662f\u4e00\u4e2a\u975e\u5e38\u5173\u952e\u7684\u7ed3\u6784\u4f53\uff1bInnoDB\u5b58\u50a8\u5f15\u64ce\u901a\u8fc7\u56de\u6eda\u6bb5\u6765\u5bf9undo log\u8fdb\u884c\u7ec4\u7ec7\u548c\u7ba1\u7406\uff0c\u6240\u4ee5\u9996\u5148\u6211\u4eec\u9700\u8981\u5f04\u6e05\u695a\u56de\u6eda\u6bb5\u662f\u5982\u4f55\u5206\u914d\u4e0e\u4f7f\u7528\u7684\uff0c\u4e4b\u540e\u518d\u9610\u8ff0undo log\u5177\u4f53\u662f\u5982\u4f55\u8bb0\u5f55\u7684\u30021. \u5206\u914d\u56de\u6eda\u6bb5\u5f53\u5f00\u542f\u4e00\u4e2a\u4e8b\u52a1\u7684\u65f6\u5019\uff0c\u9700\u8981\u9884\u5148\u4e3a\u4e8b\u52a1\u5206\u914d\u4e00\u4e2a\u56de\u6eda\u6bb5\u3002\u9996\u5148\u6211\u4eec\u5c06\u4e8b\u52a1\u5206\u4e3a\u4e24\u5927\u7c7b\uff1a\u53ea\u8bfb\u4e8b\u52a1\u4e0e\u8bfb\u5199\u4e8b\u52a1\u3002\u5206\u522b\u4ece\u8fd9\u4e24\u5927\u7c7b\u4e8b\u52a1\u6765\u63a2\u8ba8\u5982\u4f55\u5206\u914d\u56de\u6eda\u6bb5\u7684\u3002\u53ea\u8bfb\u4e8b\u52a1\uff1a\u5f53\u4e8b\u52a1\u6d89\u53ca\u5230\u5bf9\u4e34\u65f6\u8868\u7684\u8bfb\u5199\u65f6\uff0c\u6211\u4eec\u9700\u8981\u4e3a\u5176\u5206\u914d\u4e00\u4e2a\u56de\u6eda\u6bb5\u5bf9\u5176\u4ea7\u751f\u7684undo log record\u8fdb\u884c\u8bb0\u5f55\uff0c\u5177\u4f53\u8c03\u7528\u94fe\u8def\u5982\u4e0b\uff1atrx_assign_rseg_temp() -&gt; get_next_temp_rseg() -&gt; (trx_sys-&gt;tmp_rsegs)trx_sys-&gt;tmp_rsegs \u5bf9\u5e94\u7684\u4e34\u65f6\u6587\u4ef6\u4e3aibtmp1\uff0c\u4e00\u822c\u6765\u8bf4\u6709128\u4e2a\u56de\u6eda\u6bb5\u3002\u8bfb\u5199\u4e8b\u52a1\uff1a\u5f53\u4e00\u4e2a\u4e8b\u52a1\u88ab\u5224\u5b9a\u4e3a\u8bfb\u5199\u6a21\u5f0f\u65f6\uff0c\u4f1a\u4e3a\u5176\u5206\u914dtrx_id\u4ee5\u53ca\u56de\u6eda\u6bb5\uff0c\u5177\u4f53\u8c03\u7528\u94fe\u8def\u5982\u4e0btrx_assign_rseg_durable() -&gt; get_next_redo_rseg() \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0| \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0-&gt;get_next_redo_rseg_from_trx_sys() -&gt; (trx_sys-&gt;rsegs) \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0| \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0-&gt;get_next_redo_rseg_from_undo_spaces() -&gt; (undo_space-&gt;rsegs())\u5f53InnoDB\u6ca1\u6709\u914d\u7f6e\u72ec\u7acbundo\u8868\u7a7a\u95f4\u65f6\uff0c\u4ecetrx_sys-&gt;rsegs\u4e3a\u8bfb\u5199\u4e8b\u52a1\u5206\u914d\u56de\u6eda\u6bb5\uff1b\u5426\u5219\u5219\u4ece undo_spaces-&gt;rsegs()\u4e3a\u5176\u5206\u914d\u56de\u6eda\u6bb5\uff1bInnoDB\u4eceMySQL 8.0.3\u5f00\u59cb\uff0c\u72ec\u7acb\u8868\u7a7a\u95f4\u4e2a\u6570\u9ed8\u8ba4\u503c\u4ece0\u6539\u4e3a2\u3002trx_sys-&gt;rsegs \u5bf9\u5e94\u7684\u6587\u4ef6\u4e3aibdata1\uff0c\u9ed8\u8ba4\u6709128\u4e2a\u56de\u6eda\u6bb5\u3002undo_space-&gt;rsegs() \u5bf9\u5e94\u7684\u6587\u4ef6\u4e3aundo_001\uff0cundo_002&#8230;\uff0c\u6700\u591a\u53ef\u6709128\u4e2aundo\u6587\u4ef6\uff0c\u6bcf\u4e2a\u6587\u4ef6\u9ed8\u8ba4128\u4e2a\u56de\u6eda\u6bb5\u3002\u5177\u4f53\u4ecersegs\u4e2d\u5206\u914d\u65f6\u91c7\u7528round-robin\u65b9\u5f0f\u8fdb\u884c\u5206\u914d\u30022. \u4f7f\u7528\u56de\u6eda\u6bb5\u5f53\u53d1\u751f\u6570\u636e\u53d8\u66f4\u65f6\uff0c\u6211\u4eec\u9700\u8981\u4f7f\u7528undo log\u8bb0\u5f55\u4e0b\u53d8\u66f4\u524d\u7684\u6570\u636e\u8bb0\u5f55\uff1b\u56e0\u6b64\u9700\u8981\u4ece\u56de\u6eda\u6bb5\u5206\u914d\u4e2d\u6765\u5206\u914d\u4e00\u4e2aundo slot\u6765\u4f9b\u4e8b\u52a1\u8bb0\u5f55undo\u3002\u8bb0\u5f55undo\u7684\u5165\u53e3\u51fd\u6570\u4e3atrx_undo_report_row_operation\uff0c\u5176\u5927\u81f4\u6d41\u7a0b\u5982\u4e0b\uff1a\u5224\u65ad\u64cd\u4f5c\u7684\u8868\u662f\u5426\u4e3a\u4e34\u65f6\u8868\uff1b\u5982\u679c\u662f\u4e34\u65f6\u8868\uff0c\u4e3a\u5176\u5206\u914d\u4e34\u65f6\u8868\u56de\u6eda\u6bb5\uff0c\u5426\u5219\u4f7f\u7528\u666e\u901a\u56de\u6eda\u6bb5\u3002\u6839\u636e\u4e8b\u52a1\u7c7b\u578b\uff0c\u901a\u8fc7trx_undo_assign_undo\u4e3a\u5176\u5206\u914dtrx_undo_t\u5bf9\u8c61\uff1b\u4e4b\u540e\u4e8b\u52a1\u4ea7\u751f\u7684undo\u8bb0\u5f55\u5728\u6b64\u5bf9\u8c61\u4e2d\u3002\u6839\u636e\u4e8b\u52a1\u7c7b\u578b\uff0c\u901a\u8fc7trx_undo_page_report_insert\/modify\uff0c\u6765\u8bb0\u5f55insert\/update\u4e8b\u52a1\u4ea7\u751f\u7684undo\u3002\u63a5\u7740\u6765\u770b\u4e00\u4e0b trx_undo_assign_undo \u51fd\u6570\u6d41\u7a0b\uff1a\u9996\u5148\u5c1d\u8bd5\u901a\u8fc7trx_undo_reuse_cached() \u6765\u83b7\u53d6\u53ef\u7528\u7684undo log\u5bf9\u8c61\u3002\u5bf9\u4e8eINSERT\u7c7b\u578b\u7684undo log\uff0c\u6211\u4eec\u4ecerseg-&gt;insert_undo_cached\u94fe\u8868\u4e0a\u83b7\u53d6undo log\u5bf9\u8c61\uff0c\u5e76\u5c06\u5176\u4ece\u94fe\u8868\u4e0a\u79fb\u9664\uff1b\u4e4b\u540e\u901a\u8fc7trx_undo_insert_header_reuse()\u91cd\u65b0\u521d\u59cb\u5316undo page\u5934\u90e8\u4fe1\u606f\u3002\u5bf9\u4e8eUPDATE\/DELETE\u7c7b\u578bundo log\uff0c\u4ecerseg-&gt;update_undo_cached\u94fe\u8868\u4e0a\u83b7\u53d6undo log\u5bf9\u8c61\uff0c\u5e76\u5c06\u5176\u4ece\u94fe\u8868\u4e0a\u79fb\u9664\uff1b\u7136\u540e\u901a\u8fc7trx_undo_header_create()\u521b\u5efa\u65b0\u7684undo log header\u3002\u7136\u540e\u4f7f\u7528trx_undo_header_add_space_for_xid() \u4f5c\u7528\u4e8e\u4e0a\u8ff0undo log\u5bf9\u8c61\uff0c\u9884\u7559XID\u5b58\u50a8\u7a7a\u95f4\u3002\u6700\u540e\u4f7f\u7528trx_undo_mem_init_for_reuse()\u521d\u59cb\u5316undo log\u5bf9\u8c61\u76f8\u5173\u4fe1\u606f\u3002\u5982\u679c\u6ca1\u6709\u7f13\u5b58\u7684undo log\u5bf9\u8c61\uff0c\u6211\u4eec\u5c31\u9700\u8981\u4f7f\u7528trx_undo_create()\u4ece\u56de\u6eda\u6bb5\u4e0a\u5206\u914d\u4e00\u4e2a\u7a7a\u95f2\u7684undo slot\uff0c\u5e76\u5206\u914d\u4e00\u4e2aundo page\uff0c\u5bf9\u5176\u521d\u59cb\u5316\u3002\u5c06\u5df2\u7ecf\u5206\u914d\u597d\u7684undo log\u5bf9\u8c61\u653e\u5165\u76f8\u5173\u7684\u94fe\u8868\u4e2d\uff08rseg-&gt;insert_undo_list\u6216rseg-&gt;update_undo_list\uff09\u3002\u6700\u540e\uff0c\u5982\u679c\u8fd9\u4e2a\u4e8b\u52a1\u65f6DDL\u64cd\u4f5c\uff0c\u9700\u8981\u5c06undo_hdr_page(\u4e8b\u52a1\u8bb0\u5f55undo log\u7684\u7b2c\u4e00\u4e2apage)\u4e2d\u7684TRX_UNDO_DICT_TRANS\u7f6e\u4e3aTRUE.undo header page\u7ed3\u6784\u53c2\u8003\u4e4b\u524d\u7684\u300aundo log\u7684\u7ec4\u7ec7\u5f62\u5f0f\u300b\u7684\u5185\u5bb9undo log\u6700\u5c0f\u7684\u5e76\u53d1\u5355\u5143\u4e3aundo slot\uff0c\u6240\u4ee5undo log\u652f\u6301\u6700\u5927\u7684\u5e76\u53d1\u4e8b\u52a1\u4e3a\uff1aundo tablespace \u6570 <em> \u56de\u6eda\u6bb5\u6570 <\/em> undo slot\u6570\u30023. undo log\u5199\u5165\u5f53\u5206\u914d\u5b8cundo slot\uff0c\u521d\u59cb\u5316\u5b8cundo log\u5bf9\u8c61\u540e\uff0c\u6211\u4eec\u5c31\u53ef\u4ee5\u8bb0\u5f55\u771f\u6b63\u7684undo log record\uff1bundo log record\u4e5f\u5206\u4e3a\u4e00\u4e0b\u4e24\u79cd\uff0cinsert undo log record\u4e0eupdate undo record\u3002\u5f53\u6570\u636e\u5e93\u9700\u8981\u4fee\u6539\u67d0\u4e2a\u6570\u636e\u8bb0\u5f55\u65f6\uff0c\u90fd\u4f1a\u5199\u5165\u4e00\u6761update undo log record\uff1b\u5f53\u63d2\u5165\u4e00\u6761\u6570\u636e\u8bb0\u5f55\u65f6\uff0c\u4f1a\u5199\u5165\u4e00\u6761insert undo log record\u3002<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209811\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0\u00a0\u5bf9\u4e8einsert undo log\u5199\u5165\u7684\u5165\u53e3\u51fd\u6570\u4e3atrx_undo_page_report_insert()Prev record offset (2)\uff1a\u672c\u6761record\u5f00\u59cb\u7684\u4f4d\u7f6e\u3002Next record offset (2)\uff1a\u4e0b\u4e00\u6761record\u5f00\u59cb\u7684\u4f4d\u7f6e\u3002Type (1)\uff1a\u6807\u8bb0undo log record\u7684\u7c7b\u578b\uff0c\u6b64\u5904\u4e00\u822c\u4e3a TRX_UNDO_INSERT_REC.Undo Number (1-11)\uff1atrx-&gt;undo_no\uff0c\u4e8b\u52a1\u7684\u7b2c\u51e0\u6761undo\u3002Table ID (1-11)\uff1a\u805a\u96c6\u7d22\u5f15\u6240\u5bf9\u5e94\u7684table id\u3002Unique Fields\uff1a\u552f\u4e00\u952e\u503c\u5bf9\u4e8eupdate undo log\u5199\u5165\u7684\u5165\u53e3\u51fd\u6570\u4e3atrx_undo_page_report_modify()Prev record offset (2)\uff1a\u540c\u4e0aNext record offset (2)\uff1a\u540c\u4e0aType+Extern Flag+Comp Info (1)\uff1aType\u4e3aundo log rec\u7684\u7c7b\u578b\uff0c\u6b64\u5904\u4e00\u822c\u6709\u4e09\u79cd\uff1aTRX_UNDO_DEL_MARK_REC: \u6807\u8bb0\u5220\u9664\u64cd\u4f5c\uff0c\u672a\u4fee\u6539\u4efb\u4f55\u5217\u503c\uff1b\u53ef\u80fd\u7531\u666e\u901a\u5220\u9664\u64cd\u4f5c\u4ea7\u751f\uff0c\u4e5f\u6709\u53ef\u80fd\u7531\u4fee\u6539\u805a\u96c6\u7d22\u5f15\u4ea7\u751f\uff0c\u56e0\u4e3a\u4fee\u6539\u805a\u96c6\u7d22\u5f15\u64cd\u4f5c\u88ab\u5206\u62c6\u4e3a\u5220\u9664+\u63d2\u5165\u64cd\u4f5c\u3002TRX_UNDO_UPD_DEL_REC: \u66f4\u65b0\u4e00\u4e2a\u5df2\u7ecf\u88ab\u5220\u9664\u7684\u8bb0\u5f55\uff1b\u5982\u67d0\u4e2a\u8bb0\u5f55\u88ab\u5220\u9664\u540e\uff0c\u5728\u5f88\u5feb\u63d2\u5165\u4e00\u4e2a\u76f8\u540c\u7684\u8bb0\u5f55\uff1b\u4e4b\u524d\u7684\u8bb0\u5f55\u82e5\u672a\u88abpurge\uff0c\u5c31\u53ef\u80fd\u91cd\u7528\u8be5\u8bb0\u5f55\u6240\u5728\u4f4d\u7f6e\u3002TRX_UNDO_UPD_EXIST_REC: \u66f4\u65b0\u4e00\u4e2a\u672a\u88ab\u6807\u8bb0\u5220\u9664\u7684\u8bb0\u5f55\uff0c\u4e5f\u5c31\u662f\u666e\u901a\u66f4\u65b0\u3002\u00a0Extern Flag\uff1a\u662f\u5426\u6709\u5916\u90e8\u5b58\u50a8\u5217\uff0c\u4ee5\u63d0\u793apurge\u7ebf\u7a0b\u53bb\u6e05\u7406\u5916\u90e8\u5b58\u50a8\u3002Comp Info\uff1a\u66f4\u65b0\u76f8\u5173\u4fe1\u606f\uff0c\u4f8b\u5982\u66f4\u65b0\u662f\u5426\u5bfc\u81f4\u7d22\u5f15\u5e8f\u53d1\u751f\u53d8\u5316\u3002Undo Number (1-11)\uff1a\u540c\u4e0aTable ID (1-11)\uff1a\u540c\u4e0aInfo Bits (1)\uff1a\u662f\u5426\u6807\u8bb0\u5220\u9664REC_INFO_DELETED_FLAG.Data Trx ID (1-11)\uff1a\u4fee\u6539\u65e7\u8bb0\u5f55\u7684\u4e8b\u52a1ID\u3002Data Roll Ptr (1-11)\uff1a\u65e7\u8bb0\u5f55\u7684\u56de\u6eda\u6307\u9488\u3002Unique Fields\uff1a\u552f\u4e00\u952e\u503cUpdate Get N Fields (1-5): \u66f4\u65b0\u7684\u5217\u6570\u3002UPD Old Columns\uff1a\u53d1\u751f\u66f4\u65b0\u65f6\uff0c\u65e7\u8bb0\u5f55\u7684\u5185\u5bb9\u3002Delete Fileds len (2): \u5220\u9664\u7684\u5217\u6570\u3002DEL Old Columns\uff1a\u53d1\u751f\u5220\u9664\u65f6\uff0c\u65e7\u8bb0\u5f55\u7684\u5185\u5bb9\uff1b\u53d1\u751f\u5220\u9664\u65f6\u5e76\u4e0d\u603b\u662f\u8bb0\u5f55\u65e7\u8bb0\u5f55\uff0c\u53ea\u6709ord_part=1\u4e5f\u5c31\u662f\u8bf4\u6b64\u5b57\u6bb5\u4e3an_uniq\u4e4b\u4e00\u7684\u5b57\u6bb5\uff0c\u624d\u4f1a\u8bb0\u5f55\u65e7\u5b57\u6bb5\u3002\u5728\u5199\u5165\u8fc7\u7a0b\u4e2d\uff0c\u53ef\u80fd\u51fa\u73b0undo page\u7a7a\u95f4\u4e0d\u8db3\u7684\u60c5\u51b5\uff1b\u5f53\u51fa\u73b0\u8fd9\u79cd\u60c5\u51b5\uff0c\u6211\u4eec\u9700\u8981\u901a\u8fc7trx_undo_erase_page_end()\u6765\u6e05\u9664\u521a\u521a\u5199\u5165\u7684\u533a\u57df\uff0c\u7136\u540e\u901a\u8fc7trx_undo_add_page()\u7533\u8bf7\u4e00\u4e2a\u65b0\u7684undo page\u52a0\u5165\u5230undo page list\uff0c\u540c\u65f6\u5c06undo-&gt;last_page_no\u6307\u5411\u65b0\u7684undo page\uff0c\u6700\u540e\u91cd\u8bd5\u5199\u5165\u3002\u5b8c\u6210undo log record\u7684\u5199\u5165\u540e\uff0c\u901a\u8fc7trx_undo_build_roll_ptr()\u6784\u5efa\u65b0\u7684\u56de\u6eda\u6307\u9488\u8fd4\u56de\uff1b\u901a\u8fc7\u56de\u6eda\u6307\u9488\u6211\u4eec\u53ef\u4ee5\u627e\u5230\u76f8\u5173\u8bb0\u5f55\u7684undo log record\uff0c\u4ece\u800c\u6784\u5efa\u51fa\u65e7\u7248\u672c\u7684\u6570\u636e\uff1b\u56de\u6eda\u6307\u9488\u5c06\u4f1a\u8bb0\u5f55\u5728\u805a\u96c6\u7d22\u5f15\u8bb0\u5f55\u4e2d\u3002undo log\u7684\u5e94\u7528\u6211\u4eec\u901a\u8fc7\u4e4b\u524d\u7684\u4ecb\u7ecd\u5df2\u7ecf\u4e86\u89e3\u5230\uff0c undo log\u7684\u7ec4\u7ec7\u65b9\u5f0f\u4e0e\u5206\u914d\u8bb0\u5f55\uff1b\u90a3\u4e48\u540e\u9762\u6211\u4eec\u7ee7\u7eed\u4ecb\u7ecdundo log\u4e3b\u8981\u7684\u5e94\u7528\u662f\u4ec0\u4e48\u3002undo log\u7684\u5e94\u7528\u4e3b\u8981\u6709\u4e24\u65b9\u9762\uff1a\u4e8b\u52a1\u56de\u6eda\uff0c\u5d29\u6e83\u6062\u590d\uff1b\u6b64\u529f\u80fd\u4e3b\u8981\u6ee1\u8db3\u4e86\u4e8b\u52a1\u7684\u539f\u5b50\u6027\uff0c\u7b80\u5355\u7684\u8bf4\u5c31\u662f\u8981\u4e48\u505a\u5b8c\uff0c\u8981\u4e48\u4e0d\u505a\u3002\u56e0\u4e3a\u6570\u636e\u5e93\u5728\u4efb\u4f55\u65f6\u5019\u90fd\u53ef\u80fd\u53d1\u751f\u5b95\u673a\uff1b\u5305\u62ec\u505c\u7535\uff0c\u8f6f\u786c\u4ef6bug\u7b49\u3002\u90a3\u6570\u636e\u5e93\u5c31\u9700\u8981\u4fdd\u8bc1\u4e0d\u7ba1\u53d1\u751f\u4efb\u4f55\u60c5\u51b5\uff0c\u5728\u91cd\u542f\u6570\u636e\u5e93\u65f6\u90fd\u80fd\u6062\u590d\u5230\u4e00\u4e2a\u4e00\u81f4\u6027\u7684\u72b6\u6001\uff1b\u8fd9\u4e2a\u4e00\u81f4\u6027\u7684\u72b6\u6001\u662f\u6307\u6b64\u65f6\u6240\u6709\u4e8b\u52a1\u8981\u4e48\u5904\u4e8e\u63d0\u4ea4\uff0c\u8981\u4e48\u5904\u4e8e\u672a\u5f00\u59cb\u7684\u72b6\u6001\uff0c\u4e0d\u5e94\u8be5\u6709\u4e8b\u52a1\u5904\u4e8e\u6267\u884c\u4e86\u4e00\u534a\u7684\u72b6\u6001\uff1b\u6240\u4ee5\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7undo log\u5728\u6570\u636e\u5e93\u91cd\u542f\u65f6\u628a\u6b63\u5728\u63d0\u4ea4\u7684\u4e8b\u52a1\u5b8c\u6210\u63d0\u4ea4\uff0c\u6d3b\u8dc3\u7684\u4e8b\u52a1\u56de\u6eda\uff0c\u8fd9\u6837\u5c31\u4fdd\u8bc1\u4e86\u4e8b\u52a1\u7684\u539f\u5b50\u6027\uff0c\u4ee5\u6b64\u6765\u8ba9\u6570\u636e\u5e93\u6062\u590d\u5230\u4e00\u4e2a\u4e00\u81f4\u6027\u7684\u72b6\u6001\u3002\u591a\u7248\u672c\u5e76\u53d1\u63a7\u5236(MVCC)\uff0c\u6b64\u529f\u80fd\u4e3b\u8981\u6ee1\u8db3\u4e86\u4e8b\u52a1\u7684\u9694\u79bb\u6027\uff0c\u7b80\u5355\u7684\u8bf4\u5c31\u662f\u4e0d\u540c\u6d3b\u8dc3\u4e8b\u52a1\u7684\u6570\u636e\u4e92\u76f8\u53ef\u80fd\u662f\u4e0d\u53ef\u89c1\u7684\u3002\u56e0\u4e3a\u5982\u679c\u4e24\u4e2a\u6d3b\u8dc3\u7684\u4e8b\u52a1\u5f7c\u6b64\u53ef\u89c1\uff0c\u90a3\u4e48\u4e00\u4e2a\u4e8b\u52a1\u5c06\u4f1a\u770b\u5230\u53e6\u4e00\u4e2a\u4e8b\u52a1\u6b63\u5728\u4fee\u6539\u7684\u6570\u636e\uff0c\u8fd9\u6837\u4f1a\u53d1\u751f\u6570\u636e\u9519\u4e71\uff1b\u6240\u4ee5\u6211\u4eec\u53ef\u4ee5\u501f\u52a9undo log\u8bb0\u5f55\u7684\u5386\u53f2\u7248\u672c\u6570\u636e\uff0c\u6765\u6062\u590d\u51fa\u5bf9\u4e8e\u4e00\u4e2a\u4e8b\u52a1\u53ef\u89c1\u7684\u6570\u636e\uff0c\u6765\u6ee1\u8db3\u5176\u8bfb\u53d6\u6570\u636e\u7684\u8bf7\u6c42\u3002\u6211\u4eec\u63a5\u4e0b\u6765\u5c31\u8be6\u7ec6\u4ecb\u7ecd\u4e0a\u9762\u4e24\u4e2a\u529f\u80fdundo log\u662f\u5982\u4f55\u5b9e\u73b0\u7684\u30021. \u5d29\u6e83\u6062\u590d\u5728InnoDB\u56e0\u4e3a\u67d0\u4e9b\u539f\u56e0\u505c\u6b62\u8fd0\u884c\u540e\uff1b\u91cd\u542fInnoDB\u65f6\uff0c\u53ef\u80fd\u5b58\u5728\u4e00\u4e2a\u4e0d\u4e00\u81f4\u7684\u72b6\u6001\uff0c\u8fd9\u4e2a\u65f6\u5019\u6211\u4eec\u5c31\u9700\u8981\u628aMySQL\u6062\u590d\u5230\u4e00\u4e2a\u4e00\u81f4\u7684\u72b6\u6001\u6765\u4fdd\u8bc1\u6570\u636e\u5e93\u7684\u53ef\u7528\u6027\u3002\u8fd9\u4e2a\u6062\u590d\u8fc7\u7a0b\u4e3b\u8981\u5206\u4e0b\u9762\u8fd9\u4e48\u51e0\u6b65\uff1a\u628a\u6700\u65b0\u7684undo log\u4eceredo log\u4e2d\u6062\u590d\u51fa\u6765\uff0c\u56e0\u4e3aundo log\u662f\u53d7redo log\u4fdd\u62a4\u7684\u3002\u6839\u636e\u6700\u65b0\u7684undo log\u6784\u5efa\u51faInnoDB\u5d29\u6e83\u524d\u7684\u72b6\u6001\u3002\u56de\u6eda\u90a3\u4e9b\u8fd8\u6ca1\u6709\u63d0\u4ea4\u7684\u4e8b\u52a1\u3002\u7ecf\u8fc7\u4e0a\u9762\u8fd9\u4e09\u6b65\u540e\uff0cInnoDB\u5c31\u53ef\u4ee5\u6062\u590d\u5230\u4e00\u4e2a\u4e00\u81f4\u7684\u72b6\u6001\uff0c\u5e76\u4e14\u5bf9\u5916\u63d0\u4f9b\u670d\u52a1\u3002\u4e0b\u9762\u6211\u4eec\u8be6\u7ec6\u7684\u6765\u4ecb\u7ecd\u8fd9\u4e09\u90e8\u5206\u7684\u5177\u4f53\u8fc7\u7a0b\uff1a1.1 undo log\u7684\u6062\u590d\u56e0\u4e3aundo log\u53d7\u5230redo log\u7684\u4fdd\u62a4\uff0c\u6240\u4ee5\u6211\u4eec\u53ea\u9700\u8981\u6839\u636e\u6700\u65b0\u7684redo log\u5c31\u53ef\u4ee5\u628aundo log\u6062\u590d\u5230\u6700\u65b0\u7684\u72b6\u6001\uff1b\u5177\u4f53\u7684\u8c03\u7528\u8fc7\u7a0b\u5982\u4e0b\uff1arecv_recovery_from_checkpoint_start()\/\/ \u4ece\u6700\u65b0\u7684\u4e00\u4e2alog checkpoint\u5f00\u59cb\u8bfb\u53d6redo log\u5e76\u5e94\u7528\u3002 \u00a0 \u00a0 | \u00a0 \u00a0 -&gt; recv_recovery_begin() \/\/ \u5c06redo log\u8bfb\u53d6\u5230log buffer\u4e2d\uff0c\u5e76\u5c06\u5176parse\u5230redo hash\u4e2d \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 | \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -&gt; recv_scan_log_recs() \/\/ \u626b\u63cf log buffer\u4e2d\u7684redo log\uff0c\u5e76\u5c06redo hash\u4e2d\u7684redo log\u5e94\u7528 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 | \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -&gt; recv_apply_hashed_log_recs() \/\/ \u5e94\u7528redo log\u5230\u5176\u5bf9\u5e94\u7684page\u4e0a\u3002 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 | \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -&gt;recv_apply_log_rec()-&gt;recv_recover_page()-&gt;recv_parse_or_apply_log_rec_body() -&gt; MLOG_UNDO_INSERT\u2026\u7ecf\u8fc7\u4e0a\u8ff0\u7684\u6d41\u7a0b\u4e4b\u540e\uff0cundo log\u5c31\u53ef\u4ee5\u6062\u590d\u5230InnoDB\u5d29\u6e83\u524d\u7684\u6700\u65b0\u7684\u72b6\u6001\uff1b\u867d\u7136undo log\u5df2\u7ecf\u6062\u590d\u5230\u6700\u65b0\u7684\u72b6\u6001\uff0c\u4f46\u662fInnoDB\u8fd8\u6ca1\u6709\u6062\u590d\u5230\u5d29\u6e83\u524d\u7684\u6700\u65b0\u72b6\u6001\uff1b\u6240\u4ee5\u4e0b\u4e00\u6b65\u6211\u4eec\u5c31\u9700\u8981\u6839\u636e\u6700\u65b0\u7684undo log\u628aInnoDB\u5d29\u6e83\u524d\u7684\u5185\u5b58\u7ed3\u6784\u90fd\u6062\u590d\u51fa\u6765\u30021.2 \u6784\u5efaInnoDB\u5d29\u6e83\u524d\u7684\u72b6\u6001\u6784\u5efaInnoDB\u5d29\u6e83\u524d\u7684\u72b6\u6001\uff0c\u4e3b\u8981\u662f\u6062\u590d\u5d29\u6e83\u524d\u6700\u65b0\u4e8b\u52a1\u7cfb\u7edf\u7684\u72b6\u6001\uff1b\u901a\u8fc7\u8be5\u72b6\u6001\u6211\u4eec\u53ef\u4ee5\u77e5\u9053\u90a3\u4e9b\u4e8b\u52a1\u5df2\u7ecf\u63d0\u4ea4\uff0c\u90a3\u4e9b\u4e8b\u52a1\u8fd8\u672a\u63d0\u4ea4\uff0c\u4ee5\u53ca\u90a3\u4e9b\u4e8b\u52a1\u8fd8\u672a\u5f00\u59cb\u3002\u6211\u4eec\u4ece\u524d\u9762\u4e24\u7ae0\u7684\u4ecb\u7ecd\uff0c\u56de\u6eda\u6bb5\u4e0d\u7ba1\u5728\u5185\u5b58\u4e2d\u8fd8\u662f\u5728\u6587\u4ef6\u4e2d\u90fd\u662f\u7ec4\u7ec7undo log\u7684\u91cd\u8981\u6570\u636e\u7ed3\u6784\uff1b\u6240\u4ee5\u6211\u4eec\u9996\u5148\u9700\u8981\u628a\u56de\u6eda\u6bb5\u7684\u5185\u5b58\u7ed3\u6784\u6062\u590d\u51fa\u6765\uff0c\u7136\u540e\u6839\u636e\u5185\u5b58\u4e2d\u7684\u56de\u6eda\u6bb5\uff0c\u628a\u6d3b\u8dc3\u7684\u4e8b\u52a1\u6062\u590d\u51fa\u6765\u3002\u5176\u5177\u4f53\u8fc7\u7a0b\u5728\u51fd\u6570trx_sys_init_at_db_start()\u4e2d\u5b9e\u73b0\uff0c\u5176\u5927\u81f4\u6b65\u9aa4\u5982\u4e0b\uff1a\u901a\u8fc7trx_rsegs_init()\u626b\u63cf\u6587\u4ef6\u4e2d\u7684\u56de\u6eda\u6bb5\u7ed3\u6784\uff0c\u6765\u628arseg\u7684\u5185\u5b58\u7ed3\u6784\u6062\u590d\u51fa\u6765\u3002\u901a\u8fc7trx_rseg_mem_create()\u628alast_page_no\uff0clast_offset\uff0clast_trx_no\uff0clast_del_marks\u4ece\u6587\u4ef6\u4e2d\u8bfb\u53d6\u4e0a\u6765\u3002\u7136\u540e\u901a\u8fc7trx_undo_lists_init()\u628arseg\u7684\u56db\u4e2a\u94fe\u8868\uff1ainsert_undo_list\uff0cinsert_undo_cached\uff0cupdate_undo_list\uff0cupdate_undo_cached\u4ece\u78c1\u76d8\u4e0a\u6062\u590d\u51fa\u6765\u3002\u5728rseg\u5185\u5b58\u7ed3\u6784\u6062\u590d\u597d\u4e4b\u540e\uff0c\u6211\u4eec\u518d\u901a\u8fc7trx_lists_init_at_db_start()\u628a\u6d3b\u8dc3\u7684\u4e8b\u52a1\u4ecerseg\u4e2d\u6062\u590d\u51fa\u6765\u3002\u901a\u8fc7trx_resurrect_insert()\u6062\u590d\u6d3b\u8dc3\u7684\u63d2\u5165\u7c7b\u578b\u7684\u4e8b\u52a1\u3002\u901a\u8fc7trx_resurrect_update()\u6062\u590d\u6d3b\u8dc3\u7684\u66f4\u65b0\u7c7b\u578b\u7684\u4e8b\u52a1\u3002\u81f3\u6b64\uff0c\u6211\u4eec\u5c31\u5df2\u7ecf\u628aInnoDB\u5d29\u6e83\u524d\u7684\u5185\u5b58\u548c\u6587\u4ef6\u72b6\u6001\u90fd\u5df2\u7ecf\u6062\u590d\u51fa\u6765\u4e86\uff1b\u5176\u5b9e\u8fd9\u4e2a\u65f6\u5019InnoDB\u5df2\u7ecf\u53ef\u4ee5\u5bf9\u5916\u63d0\u4f9b\u670d\u52a1\u4e86\uff0c(\u6bd5\u7adf\u5185\u5b58\u548c\u6587\u4ef6\u72b6\u6001\u90fd\u5c31\u7eea\u540e\u6211\u4eec\u4e5f\u5c31\u53ef\u4ee5\u4fdd\u6301\u4e00\u81f4\u6027\u4e86)\uff1b\u90a3\u4e48\u6700\u540e\u4e00\u6b65\u7684\u4e8b\u52a1\u56de\u6eda\u5c31\u53ef\u4ee5\u4ea4\u7ed9\u540e\u53f0\u7ebf\u7a0b\u6765\u6162\u6162\u505a\u4e8b\u52a1\u56de\u6eda\uff0c\u4e0d\u5f71\u54cd\u4e3b\u7ebf\u7a0b\u5bf9\u5916\u63d0\u4f9b\u670d\u52a1\u4e86\u30021.3 \u4e8b\u52a1\u56de\u6eda\u4e8b\u52a1\u9700\u8981\u56de\u6eda\u4e3b\u8981\u6709\u4e24\u79cd\u60c5\u51b5\uff1a\u4e8b\u52a1\u53d1\u751f\u5f02\u5e38\uff1a\u5982\u53d1\u751f\u5728\u5d29\u6e83\u6062\u590d\u65f6\uff1b\u5176\u6d3b\u8dc3\u4e8b\u52a1\u867d\u7136\u88ab\u6062\u590d\u51fa\u6765\uff0c\u4f46\u662f\u65e0\u6cd5\u7ee7\u7eed\uff0c\u9700\u8981\u5c06\u5176\u56de\u6eda\u3002\u4e8b\u52a1\u88ab\u663e\u5f0f\u56de\u6eda\uff1a\u5982\u7528\u6237\u6253\u5f00\u4e00\u4e2a\u4e8b\u52a1\uff0c\u6267\u884c\u5b8c\u67d0\u4e9b\u64cd\u4f5c\u540e\u9700\u8981\u5c06\u5176\u56de\u6eda\u3002\u90a3\u4e48\u5728\u56de\u6eda\u65f6\uff0c\u6211\u4eec\u5c31\u9700\u8981\u501f\u52a9undo log\u4e2d\u7684\u65e7\u6570\u636e\u6765\u628a\u4e8b\u52a1\u6062\u590d\u5230\u4e4b\u524d\u7684\u72b6\u6001\uff1b\u5176\u5165\u53e3\u51fd\u6570\u4e3arow_undo_step()\uff1b\u5176\u64cd\u4f5c\u5c31\u662f\u901a\u8fc7undo log\u6765\u8bfb\u53d6\u65e7\u7684\u6570\u636e\u8bb0\u5f55\uff0c\u7136\u540e\u505a\u9006\u5411\u64cd\u4f5c\uff1b\u4e3b\u8981\u5206\u4e3a\u4e0b\u9762\u8fd9\u4e48\u51e0\u7c7b\uff1a\u5bf9\u4e8e\u6807\u8bb0\u5220\u9664\u7684\u8bb0\u5f55\u6e05\u7406\u5220\u9664\u6807\u8bb0\u3002\u5bf9\u4e8ein-place\u66f4\u65b0\uff0c\u5c06\u6570\u636e\u66f4\u65b0\u4e3a\u8001\u7248\u672c\u3002\u5bf9\u4e8e\u63d2\u5165\u64cd\u4f5c\uff0c\u5220\u9664\u805a\u96c6\u7d22\u5f15\u8bb0\u5f55\u548c\u4e8c\u7ea7\u7d22\u5f15\u8bb0\u5f55\u3002\u5148\u901a\u8fc7row_undo_ins_remove_sec_rec()\u5220\u9664\u4e8c\u7ea7\u7d22\u5f15\u8bb0\u5f55\u3002\u518d\u901a\u8fc7row_undo_ins_remove_clust_rec()\u5220\u9664\u805a\u96c6\u7d22\u5f15\u8bb0\u5f55\u30022. \u591a\u7248\u672c\u5e76\u53d1\u63a7\u5236(MVCC)\u591a\u7248\u672c\u5e76\u53d1\u63a7\u5236\u7b80\u5355\u7684\u8bf4\u5c31\u662f\u5f53\u524d\u4e8b\u52a1\u53ea\u80fd\u770b\u89c1\u5df2\u7ecf\u63d0\u4ea4\u7684\u6570\u636e\u8bb0\u5f55\uff0c\u770b\u4e0d\u5230\u6b63\u5728\u4fee\u6539\u7684\u6570\u636e\u8bb0\u5f55\u3002\u6240\u4ee5\u6211\u4eec\u53ea\u8981\u5f04\u6e05\u695a\u90a3\u4e9b\u4e8b\u52a1\u5bf9\u4e8e\u5f53\u524d\u4e8b\u52a1\u662f\u5df2\u7ecf\u63d0\u4ea4\u7684\uff0c\u90a3\u4e9b\u4e8b\u52a1\u5bf9\u4e8e\u5f53\u524d\u4e8b\u52a1\u662f\u6d3b\u8dc3\u7684\u3002\u4e3a\u4e86\u5b9e\u73b0\u4e0a\u8ff0\u7684\u529f\u80fd\u6211\u4eec\u5148\u4ecb\u7ecd\u51e0\u4e2a\u6bd4\u8f83\u5173\u952e\u7684\u6982\u5ff5\uff1atrx::id\uff1a\u4e8b\u52a1\u5f00\u59cb\u7684\u903b\u8f91\u65f6\u95f4\uff0c\u4e5f\u53eb\u4e8b\u52a1ID\uff0c\u5728\u4e8b\u52a1\u5f00\u59cb\u65f6\u901a\u8fc7trx_start_low()\u5206\u914d\u3002trx::no\uff1a\u4e8b\u52a1\u7ed3\u675f\u7684\u903b\u8f91\u65f6\u95f4\uff0c\u5728\u4e8b\u52a1\u7ed3\u675f\u7684\u65f6\u5019\u901a\u8fc7trx_commit_low()\u5206\u914d\u3002trx_sys::rw_trx_ids\uff1a\u5f53\u524d\u6d3b\u8dc3\u7684\u4e8b\u52a1ID\uff1b\u4e8b\u52a1\u5728\u5f00\u59cb\u65f6ID\u4f1a\u88ab\u6dfb\u52a0\u81f3\u6b64\u6570\u636e\u7ed3\u6784\u4e2d\uff1b\u4e8b\u52a1\u63d0\u4ea4\u65f6ID\u4f1a\u88ab\u4ece\u6b64\u6570\u636e\u7ed3\u6784\u4e2d\u5220\u9664\u3002\u5728\u6784\u9020\u4e00\u6761\u6570\u636e\u8bb0\u5f55\u65f6\uff0c\u6211\u4eec\u9664\u4e86\u5728\u6570\u636e\u8bb0\u5f55\u4e2d\u6dfb\u52a0\u7528\u6237\u81ea\u4e3b\u6dfb\u52a0\u7684\u6570\u636e\u5217\uff0c\u7cfb\u7edf\u8fd8\u4f1a\u81ea\u52a8\u5206\u914d\u4e00\u4e9b\u7cfb\u7edf\u5217\uff0c\u5177\u4f53\u5305\u62ec\uff1aDATA_TRX_ID\uff1a\u4fee\u6539\u8fc7\u6b64\u884c\u6570\u636e\u8bb0\u5f55\u7684\u6700\u65b0\u4e8b\u52a1ID\u3002DATA_ROLL_PTR\uff1a\u6307\u5411\u8fd9\u6761\u6570\u636e\u8bb0\u5f55\u7684\u4e0a\u4e00\u4e2a\u7248\u672c\u7684\u6307\u9488\uff0c\u4e0a\u4e00\u7248\u6570\u636e\u5728undo log\u4e2d\u3002\u901a\u8fc7\u4e0a\u9762\u51e0\u4e2a\u6570\u636e\u7ed3\u6784\u7684\u4ecb\u7ecd\uff0c\u6211\u4eec\u5927\u6982\u4e86\u89e3\u4e86\u4e00\u4e9b\u57fa\u672c\u6982\u5ff5\uff1b\u4f46\u662f\u8fd9\u5bf9\u4e8e\u4e00\u4e2a\u4e8b\u52a1\u6765\u5224\u65ad\u90a3\u4e9b\u4e8b\u52a1\u5bf9\u5b83\u662f\u5df2\u7ecf\u63d0\u4ea4\u7684\uff0c\u90a3\u4e9b\u4e8b\u52a1\u5bf9\u5b83\u662f\u6d3b\u8dc3\u7684\u8fd8\u662f\u8fdc\u8fdc\u4e0d\u591f\u7684\uff1b\u6240\u4ee5\u6211\u4eec\u63a5\u4e0b\u6765\u4ecb\u7ecdMVCC\u4e2d\u6700\u91cd\u8981\u7684\u4e00\u4e2a\u6570\u636e\u7ed3\u6784\uff1a\u89c6\u56fe\uff0c\u4e5f\u5c31\u662fread view\u30022.1 \u89c6\u56fe\u6bcf\u4e00\u4e2a\u4e8b\u52a1\u5728\u8bfb\u53d6\u6570\u636e\u65f6\u90fd\u4f1a\u88ab\u5206\u914d\u4e00\u4e2a\u89c6\u56fe\uff0c\u901a\u8fc7\u89c6\u56fe\u5c31\u53ef\u4ee5\u6765\u5224\u65ad\u5176\u4ed6\u4e8b\u52a1\u5bf9\u6570\u636e\u8bb0\u5f55\u7684\u53ef\u89c1\u6027\u3002\u4e0b\u9762\u6211\u4eec\u6765\u5177\u4f53\u4ecb\u7ecd\u4e00\u4e0b\u89c6\u56fe\u662f\u5982\u4f55\u8fd0\u4f5c\u7684\u3002\u5206\u914d\uff1a\u4e3b\u8981\u901a\u8fc7trx_assign_read_view()\u6765\u7ed9\u4e00\u4e2a\u4e8b\u52a1\u5206\u914d\u89c6\u56fe\uff1b\u5728\u4e8b\u52a1\u7684\u9694\u79bb\u7ea7\u522b\u662fConsistent Snapshot \u6216 Read Repeatable\u65f6\uff0c\u4e8b\u52a1\u5f00\u59cb\u65f6\u4f1a\u7ed9\u5176\u5206\u914d\uff1b\u5176\u4ed6\u60c5\u51b5\u4e0b\u5f53\u4e8b\u52a1\u9700\u8981\u8bfb\u53d6\u6570\u636e\u65f6\u5c06\u4f1a\u7ed9\u5176\u5206\u914d\u4e00\u4e2a\u89c6\u56fe\u3002\u56de\u6536\uff1a\u4e8b\u52a1\u7ed3\u675f\u65f6\uff0c\u4f1a\u901a\u8fc7view_close()\u5bf9\u5176\u89c6\u56fe\u8fdb\u884c\u56de\u6536\u3002\u51e0\u4e2a\u5173\u952e\u6570\u636e\u7ed3\u6784\uff1am_low_limit_id\uff1a\u9ad8\u6c34\u4f4d\uff0c\u5206\u914d\u65f6\u53d6trx_sys::max_trx_id\uff0c\u4e5f\u5c31\u662f\u53d6\u5f53\u524d\u8fd8\u6ca1\u6709\u88ab\u5206\u914d\u7684\u4e8b\u52a1ID\u3002m_up_limit_id\uff1a\u4f4e\u6c34\u4f4d\uff0c\u5982\u679cm_ids\u4e0d\u4e3a\u7a7a\uff0c\u53d6\u5176\u6700\u5c0f\u503c\uff0c\u5426\u5219\u53d6trx_sys::max_trx_id\u3002m_ids\uff1a\u5728\u6b64\u89c6\u56fe\u521d\u59cb\u5316\u65f6\uff0c\u901a\u8fc7copy_trx_ids()\u4ecetrx_sys::rw_trx_ids\u62f7\u8d1d\u4e00\u4efd\u6d3b\u8dc3\u4e8b\u52a1ID(\u4e0d\u5305\u542b\u5f53\u524d\u4e8b\u52a1ID)\u3002\u90a3\u4e48\u6709\u4e86\u4e0a\u9762\u8fd9\u4e9b\u6570\u636e\u6211\u4eec\u5c31\u53ef\u4ee5\u5224\u65ad\u90a3\u4e9b\u4e8b\u52a1\u5bf9\u4e8e\u6b64\u89c6\u56fe\u662f\u6d3b\u8dc3\u7684\uff0c\u90a3\u4e9b\u4e8b\u52a1\u5bf9\u4e8e\u6b64\u89c6\u56fe\u662f\u5df2\u7ecf\u63d0\u4ea4\u7684\u3002\u90a3\u4e9b\u4e8b\u52a1\u5bf9\u4e8e\u6b64\u89c6\u56fe\u662f\u6d3b\u8dc3\u7684\uff1atrx_id &gt; read_view::m_low_limit_idread_view::m_up_limit_id &lt; trx_id &lt; read_view::m_low_limit_id\uff0c\u5e76\u4e14 trx_id \u5c5e\u4e8e trx_t::read_view::m_ids\u5982\u679c\u7ed9\u5b9a\u4e00\u4e2atrx_id\u6ee1\u8db3\u4e0a\u9762\u4e24\u4e2a\u6761\u4ef6\u5176\u4e2d\u4e4b\u4e00\uff0c\u90a3\u4e48\u8fd9\u4e2a\u4e8b\u52a1\u5bf9\u4e8e\u6b64\u89c6\u56fe\u5c31\u662f\u6d3b\u8dc3\u7684\u3002\u90a3\u4e9b\u4e8b\u52a1\u5bf9\u4e8e\u6b64\u89c6\u56fe\u662f\u5df2\u7ecf\u63d0\u4ea4\u7684\uff1atrx id &lt; read_view::m_up_limit_idread_view::m_up_limit_id &lt; trx id &lt; read_view::m_low_limit_id\uff0c\u5e76\u4e14 trx id \u4e0d\u5c5e\u4e8e trx_t::read_view::m_ids\u5982\u679c\u7ed9\u5b9a\u4e00\u4e2atrx_id\u6ee1\u8db3\u4e0a\u9762\u4e24\u4e2a\u6761\u4ef6\u5176\u4e2d\u4e4b\u4e00\uff0c\u90a3\u4e48\u8fd9\u4e2a\u4e8b\u52a1\u5bf9\u4e8e\u6b64\u89c6\u56fe\u5c31\u662f\u5df2\u7ecf\u63d0\u4ea4\u7684\u30022.2 \u6570\u636e\u53ef\u89c1\u6027\u901a\u8fc7\u4e0a\u9762\u7684\u4ecb\u7ecd\uff0c\u90a3\u4e48\u4e00\u4e2a\u4e8b\u52a1\u5c31\u53ef\u4ee5\u901a\u8fc7\u6b64\u4e8b\u52a1\u7684\u89c6\u56fe\u6765\u5bf9\u6570\u636e\u8bb0\u5f55\u5224\u65ad\u53ef\u89c1\u6027\u4e86\u3002\u5177\u4f53\u662f\u901a\u8fc7ReadView::changes_visible()\u6765\u5224\u65ad\u53ef\u89c1\u6027\u7684\uff0c\u5177\u4f53\u5982\u4e0b\uff1a\u5047\u8bbe\u4e00\u4e2a\u4e8b\u52a1\u4e3aT\uff0ctrx_id\u4e3a\u8bb0\u5f55R\u4e2d\u7684DATA_TRX_ID\uff1atrx_id &gt; read_view::m_low_limit_id\uff0cT \u4e0d\u53ef\u89c1 Rtrx_id &lt; read_view::m_up_limit_id\uff0cT \u53ef\u89c1 Rread_view::m_up_limit_id =&lt; trx_id &lt;= read_view::m_low_limit_id\u65f6\uff0c\u5982\u679ctrx_id \u5c5e\u4e8e trx_t::read_view::m_ids \u65f6\uff0cT \u4e0d\u53ef\u89c1 R\u3002\u5426\u5219\u53ef\u89c1 R\u5982\u679cT\u5bf9R\u4e0d\u53ef\u89c1\uff0c\u5c31\u9700\u8981R\u4e2d\u7684DATA_ROLL_PTR\u6765\u6784\u9020\u51fa\u4e0a\u4e00\u4e2a\u6570\u636e\u9875\u7248\u672c\uff0c\u76f4\u81f3\u8bb0\u5f55\u53ef\u89c1\u3002\u6211\u4eec\u901a\u8fc7\u4e0b\u9762\u4e00\u4e2a\u4f8b\u5b50\u6765\u8bf4\u660e\u53ef\u89c1\u6027\u3002<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209812\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0undo log \u7684\u6e05\u7406\u6211\u4eec\u901a\u8fc7\u4e4b\u524d\u7684\u7cfb\u5217\u6587\u7ae0\u5df2\u7ecf\u4e86\u89e3\u5230undo log\u5728\u78c1\u76d8\u548c\u5185\u5b58\u4e2d\u662f\u5982\u4f55\u7ec4\u7ec7\u7684\uff1bundo log\u662f\u5982\u4f55\u5206\u914d\u7684\uff1b\u4ee5\u53caundo log\u662f\u5982\u4f55\u4f7f\u7528\u7684\u3002\u90a3\u4e48undo log\u4f1a\u4e00\u76f4\u8bb0\u5f55\u4e0b\u53bb\u4e48\uff1f\u5f53\u7136\u4e0d\u662f\uff0c\u6709\u4e9bundo log\u5982\u679c\u6ca1\u7528\u7684\u8bdd\u662f\u4f1a\u88ab\u56de\u6536\u6e05\u7406\u7684\u3002\u90a3\u4e48\u4e0b\u9762\u8fd9\u5c06\u4f1a\u4ecb\u7ecd\u90a3\u4e9bundo log\u53ef\u4ee5\u6e05\u7406\uff0c\u4ee5\u53caundo log\u662f\u600e\u4e48\u8fdb\u884c\u6e05\u7406\u7684\u30021. \u51e0\u4e2a\u5173\u952e\u7684\u6570\u636e\u7ed3\u6784\u5728\u4ecb\u7ecdundo log \u6e05\u7406\u4e4b\u524d\uff0c\u5148\u4ecb\u7ecd\u51e0\u4e2a\u5173\u952e\u7684\u6570\u636e\u7ed3\u6784\uff1b\u8fd9\u51e0\u4e2a\u6570\u636e\u7ed3\u6784\u5bf9\u4e8eundo log\u7684\u6e05\u7406\u5b9e\u73b0\u662f\u81f3\u5173\u91cd\u8981\u7684\u3002trx_sys-&gt;serialisation_list\uff1a \u91cc\u9762\u5b58\u653e\u7684\u662f\u6b63\u5728\u63d0\u4ea4\u7684\u4e8b\u52a1\uff0c\u6309\u7167trx_t::no\u6709\u5e8f\u7684\u6392\u5217\uff1b\u4e8b\u52a1\u4f1a\u5728\u5f00\u59cb\u63d0\u4ea4\u65f6\u901a\u8fc7 trx_serialisation_number_get() \u6dfb\u52a0\u81f3\u8be5\u6570\u636e\u7ed3\u6784\uff0c\u4e8b\u52a1\u7ed3\u675f\u63d0\u4ea4\u65f6\u901a\u8fc7trx_erase_lists()\u5c06\u8be5\u4e8b\u52a1\u4ece\u8be5\u6570\u636e\u7ed3\u6784\u4e2d\u79fb\u9664\u3002read_view::m_low_limit_no\uff1a\u62e5\u6709\u8be5read_view\u7684\u5bf9\u8c61\uff0c\u5bf9\u4e8etrx_t::no\u5c0f\u4e8eread_view::m_low_limit_no\u7684undo log\u90fd\u4e0d\u5728\u9700\u8981\uff1b\u8be5\u53d8\u91cf\u7684\u53d6\u503c\u65f6trx_sys-&gt;serialisation_list\u4e2d\u6700\u65e9\u7684\u4e00\u4e2a\u4e8b\u52a1\u7684trx_t::no\uff1b\u56e0\u4e3atrx_sys-&gt;serialisation_list\u5185\u6709\u5e8f\u5b58\u653e\u7684\u6b63\u5728\u63d0\u4ea4\u7684\u4e8b\u52a1\uff0c\u5982\u679c\u4e00\u4e2a\u4e8b\u52a1\u7684trx_t::no\u6bd4\u8be5\u6570\u503c\u8fd8\u5c0f\uff0c\u90a3\u4e48\u8fd9\u4e2a\u4e8b\u52a1\u4e00\u5b9a\u5df2\u7ecf\u63d0\u4ea4\u4e86\u3002TRX_RSEG_HISTORY\u4e0eTRX_UNDO_HISTORY_NODE\uff1a\u8fd9\u4e24\u4e2a\u503c\u6211\u4eec\u4e4b\u524d\u5728\u300aundolog\u7684\u7ec4\u7ec7\u5f62\u5f0f\u300b\u91cc\u7b80\u5355\u4ecb\u7ecd\u8fc7\uff0c\u8fd9\u4e24\u4e2a\u503c\u5171\u540c\u5c06\u56de\u6eda\u6bb5\u4e2d\u7684history list\u7ec4\u7ec7\u8d77\u6765\uff1b\u5728\u4e8b\u52a1\u63d0\u4ea4\u65f6\uff0c\u5982\u679c\u662fupdate\/delete\u7c7b\u578b\u7684undo log\uff0c\u5c06\u5176undo log header\u4ee5\u5934\u63d2\u6cd5\u7684\u65b9\u5f0f\u901a\u8fc7trx_purge_add_update_undo_to_history()\u52a0\u5165\u5230\u8be5\u56de\u6eda\u6bb5\u7684history list\u4e2d\uff0c\u5982\u679c\u662finsert\u7c7b\u578b\u7684undo log\u5176\u7a7a\u95f4\u4f1a\u88ab\u5f53\u573a\u91ca\u653e\uff0c\u8fd9\u662f\u56e0\u4e3ainsert\u8bb0\u5f55\u6ca1\u6709\u65e7\u7684\u7248\u672c\uff1b\u56e0\u6b64history list\u4e2d\u7684undo log header\u662f\u4ee5trx_t::no\u964d\u5e8f\u6392\u5217\u7684\uff0c\u8fd9\u91cc\u9700\u8981\u6ce8\u610f\u4e00\u4e0b\uff1ahistory list\u91cc\u9762\u7684\u8282\u70b9\u662fundo log header\u3002\u4e0b\u9762\u6211\u4eec\u901a\u8fc7\u4e00\u5e45\u56fe\u6765\u5177\u4f53\u8bf4\u660e\u4e0b\u78c1\u76d8\u4e0ahistory list\u7684\u7ed3\u6784\u3002<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209813\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0\u00a02. \u90a3\u4e9bundo log\u53ef\u4ee5\u6e05\u7406\uff1f\u5bf9\u4e8e\u4e00\u4e2a\u4e8b\u52a1\u6765\u8bf4\uff0c\u65e9\u4e8eread_view::m_low_limit_no\u7684undo log\u90fd\u4e0d\u9700\u8981\u8bbf\u95ee\u4e86\uff1b\u90a3\u4e48\u5982\u679c\u5b58\u5728\u4e00\u4e2aread view\uff0c\u5176read_view::m_low_limit_no\u6bd4\u6240\u6709read view\u7684m_low_limit_no\u90fd\u8981\u5c0f\uff0c\u90a3\u4e48\u5c0f\u4e8e\u6b64read_view::m_low_limit_no\u7684undo log\u5c31\u4e0d\u5728\u88ab\u6240\u6709\u6d3b\u8dc3\u4e8b\u52a1\u6240\u9700\u8981\u4e86\uff0c\u90a3\u4e48\u8fd9\u4e9bundo log\u5c31\u53ef\u4ee5\u6e05\u7406\u4e86\u3002\u5728read_view\u521d\u59cb\u5316\u65f6\uff0c\u4f1a\u4f7f\u7528\u5934\u63d2\u6cd5\u901a\u8fc7view_open()\u63d2\u5165\u5230\u4e00\u4e2a\u5168\u5c40\u89c6\u56fe\u94fe\u8868(MVCC::m_views)\u4e2d\uff0c\u5728\u4e8b\u52a1\u7ed3\u675f\u65f6\u901a\u8fc7view_close()\u4f1a\u4ece\u5168\u5c40\u89c6\u56fe\u94fe\u8868\u4e2d\u5c06\u6b64read view\u79fb\u9664\uff1b\u56e0\u4e3a\u662f\u987a\u5e8f\u63d2\u5165\uff0c\u6240\u4ee5\u6b64\u94fe\u8868\u4e2d\u6700\u540e\u4e00\u4e2a\u8fd8\u6ca1\u6709close\u7684\u89c6\u56fe\u5c31\u53ef\u4ee5\u770b\u505a\u662f\u6700\u8001\u7684\u4e00\u4e2a\u89c6\u56fe\uff1b\u5c0f\u4e8e\u6b64\u89c6\u56fe\u7684undo log\u53ef\u4ee5\u88ab\u6e05\u7406\uff0c\u4e00\u822c\u5c06\u6b64\u89c6\u56fe\u8d4b\u503c\u7ed9purge_sys::view\u3002\u73b0\u5728\u6211\u4eec\u5df2\u7ecf\u53ef\u4ee5\u51b3\u5b9a\u90a3\u4e9bundo log\u662f\u53ef\u4ee5\u88ab\u6e05\u7406\u7684\uff0c\u90a3\u4e48\u4e0b\u4e00\u6b65\u6211\u4eec\u8fd8\u9700\u8981\u627e\u5230\u5177\u4f53\u90a3\u4e9bundo log\u53ef\u4ee5\u6e05\u7406\u3002\u5728\u4e8b\u52a1\u63d0\u4ea4\u65f6\uff0c\u6b64\u4e8b\u52a1\u5bf9\u5e94\u7684\u56de\u6eda\u6bb5\u4f1a\u901a\u8fc7trx_serialisation_number_get()\u52a0\u5165\u5230purge_sys::purge_queue\u4e2d\u3002purge_sys::purge_queue\u662f\u4e00\u4e2a\u4ee5\u56de\u6eda\u6bb5\u4e2d\u7b2c\u4e00\u4e2a\u63d0\u4ea4\u4e8b\u52a1\u7684trx_t::no\u4e3akey\u7684\u4f18\u5148\u7ea7\u961f\u5217\u3002\u5982\u6b64\u4e00\u6765\uff0c\u4ecepurge_sys::purge_queue\u53d6\u51fa\u7684\u56de\u6eda\u6bb5\u4e2d\u4e00\u5b9a\u5305\u542b\u6700\u8001\u63d0\u4ea4\u7684\u4e8b\u52a1\uff0c\u5c06\u6b64\u4e8b\u52a1\u7684trx_t::no\u4e0epurge_sys::view\u5bf9\u6bd4\uff0c\u5373\u53ef\u5224\u65ad\u51fa\u6b64\u4e8b\u52a1\u76f8\u5173\u7684undo log\u662f\u5426\u53ef\u4ee5\u88ab\u6e05\u7406\u3002purge_sys::purge_queue\u7684\u8be6\u7ec6\u4fe1\u606f\u5982\u4e0b\u56fe\uff1a<br \/><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000042209814\" alt=\"\u56fe\u7247\" title=\"\u56fe\u7247\" loading=\"lazy\" ><br \/>\u00a0\u00a03. undo log\u600e\u4e48\u6e05\u7406\uff1f\u89e3\u51b3\u4e86\u90a3\u4e9bundo log\u53ef\u4ee5\u6e05\u7406\u7684\u95ee\u9898\u540e\uff0c\u4e0b\u9762\u63a5\u7740\u7ee7\u7eed\u770bundo log\u600e\u4e48\u8fdb\u884c\u6e05\u7406\u7684\u95ee\u9898\u3002\u5f53\u653e\u5165history list\u7684undo log\u4e14\u4e0d\u4f1a\u518d\u88ab\u8bbf\u95ee\u65f6\uff0c\u9700\u8981\u8fdb\u884c\u6e05\u7406\u64cd\u4f5c\uff0c\u53e6\u5916\u6570\u636e\u9875\u4e0a\u9762\u7684\u6807\u8bb0\u5220\u9664\u7684\u64cd\u4f5c\u4e5f\u9700\u8981\u6e05\u7406\u6389\uff0c\u6709\u4e00\u4e9bpurge\u7ebf\u7a0b\u8d1f\u8d23\u8fd9\u4e9b\u64cd\u4f5c\uff0c\u53bb\u5165\u53e3\u51fd\u6570\u4e3asrv_do_purge() -&gt; trx_purge()\uff0c\u5176\u5927\u81f4\u6d41\u7a0b\u5982\u4e0b\uff1a\u901a\u8fc7trx_sys-&gt;mvcc-&gt;clone_oldest_view()\u83b7\u53d6\u6700\u8001\u7684\u89c6\u56fe\u590d\u5236\u7ed9purge_sys::view\uff0c\u65b9\u4fbf\u4e4b\u540e\u771f\u6b63purge undo log\u65f6\u5224\u65ad\u5176\u662f\u5426\u4e0d\u4f1a\u518d\u88ab\u8bbf\u95ee\u5230\u4e86\u3002 \u00a0\u901a\u8fc7trx_purge_attach_undo_recs()\u83b7\u53d6\u9700\u8981\u88abpurge\u7684undo log\uff0c\u5176\u5927\u81f4\u6d41\u7a0b\u5982\u4e0b\uff1a \u00a0\u901a\u8fc7trx_purge_fetch_next_rec()\u5faa\u73af\u83b7\u53d6\u53ef\u4ee5\u88abpurge\u7684undo log\uff0c\u9ed8\u8ba4\u4e00\u6b21\u6700\u591a\u83b7\u53d6300\u4e2aundo log record\uff0c\u53ef\u4ee5\u901a\u8fc7innodb_purge_batch_size\u6765\u8c03\u6574\u3002 \u00a0\u5faa\u73af\u83b7\u53d6\u53ef\u4ee5\u88abpurge\u7684undo log record\u5927\u81f4\u6d41\u7a0b\u5982\u4e0b\uff1a \u00a0\u4ecepurge_sys::purge_queue\u53d6\u51fa\u7b2c\u4e00\u4e2a\u56de\u6eda\u6bb5\uff0c\u4ece\u5176history list\u4e0a\u8bfb\u53d6\u6700\u8001\u8fd8\u672a\u88abpurge\u7684\u4e8b\u52a1\u7684undo log header\u3002\u4ece\u6b64undo log header\u4f9d\u6b21\u8bfb\u53d6undo log record\u3002\u8bfb\u53d6\u5b8c\u6bd5\u540e\uff0c\u91cd\u65b0\u7edf\u8ba1\u6b64\u56de\u6eda\u6bb5\u6700\u8001\u8fd8\u672a\u88abpurge\u7684\u4e8b\u52a1\u7684\u4f4d\u70b9\uff0c\u7136\u540e\u91cd\u65b0\u653e\u5165purge_sys::purge_queue\uff1b\u6700\u540e\u56de\u5230\u7b2c\u4e00\u6b65\u3002\u00a0\u5c06\u8fd9\u4e9bundo log\u5206\u53d1\u7ed9purge\u5de5\u4f5c\u7ebf\u7a0b\uff0cpurge\u5de5\u4f5c\u7ebf\u7a0b\u7684\u5165\u53e3\u51fd\u6570\u4e3arow_purge_step()-&gt;row_purge()-&gt;row_purge_record()\u3002 \u00a0\u8fd9\u91ccpurge undo log record\u65f6\u4e3b\u8981\u5206\u4e3a\u4e24\u79cd\u60c5\u51b5\uff1a\u6e05\u7406TRX_UNDO_DEL_MARK_REC\u8bb0\u5f55\u6216\u8005\u6e05\u7406TRX_UNDO_UPD_EXIST_REC\u8bb0\u5f55\u6e05\u7406TRX_UNDO_DEL_MARK_REC\u7c7b\u578b\u7684\u8bb0\u5f55\uff0c\u9700\u8981\u901a\u8fc7row_purge_del_mark()\u5c06\u6240\u6709\u7684\u805a\u96c6\u7d22\u5f15\u4e0e\u4e8c\u7ea7\u7d22\u5f15\u8bb0\u5f55\u90fd\u6e05\u9664\u6389\u3002\u6e05\u7406TRX_UNDO_UPD_EXIST_REC\u7c7b\u578b\u7684\u8bb0\u5f55\uff0c\u9700\u8981\u901a\u8fc7row_purge_upd_exist_or_extern()\u5c06\u65e7\u7684\u4e8c\u7ea7\u7d22\u5f15\u6e05\u7406\u6389\u3002 \u00a0\u901a\u8fc7trx_purge_truncate()\u6765\u5bf9history list\u8fdb\u884c\u6e05\u7406\uff0c\u5176\u5927\u81f4\u6d41\u7a0b\u5982\u4e0b\uff1a \u00a0\u904d\u5386\u6240\u6709\u56de\u6eda\u6bb5\uff0c\u5e76\u901a\u8fc7trx_purge_truncate_rseg_history()\u5bf9\u56de\u6eda\u6bb5\u4e2d\u7684history list\u8fdb\u884c\u6e05\u7406\uff0c\u5176\u5927\u81f4\u6d41\u7a0b\u5982\u4e0b\uff1a \u00a0\u5c06history list\u6700\u540e\u4e00\u4e2a\u4e8b\u52a1\u7684undo log header\u8bfb\u53d6\u51fa\u6765\u3002\u5224\u65ad\u6b64undo log\u662f\u5426\u5df2\u7ecf\u88abpurge\uff0c\u5982\u679c\u5df2\u7ecf\u88abpurge\u5219\u7ee7\u7eed\uff1b\u5982\u679c\u6ca1\u6709\u88abpurge\u5219\u9000\u51fa\u3002\u5c06\u6b64\u4e8b\u52a1\u6240\u6709\u7684undo log\u91ca\u653e\uff0c\u5e76\u4ecehistory list\u4e0a\u5220\u9664\uff1b\u4f1a\u5230\u7b2c\u4e00\u6b65\u3002\u00a0\u5728\u8fd9\u4e4b\u540e\uff0c\u5982\u679c\u53d1\u73b0\u67d0\u4e9bundo tablespace\u7a7a\u95f4\u5360\u7528\u8fc7\u5927\uff0c\u88ab\u6807\u8bb0\u9700\u8981\u901a\u8fc7trx_purge_truncate_marked_undo()\u8fdb\u884c\u5bf9\u5176truncate\uff0c\u5176\u5927\u81f4\u6d41\u7a0b\u5982\u4e0b\uff1a\u521b\u5efa\u4e00\u4e2aundo_trunc.log\u7684\u6807\u8bb0\u6587\u4ef6\uff0c\u6765\u8868\u660e\u5f53\u524dundo tablespace\u6b63\u5728\u8fdb\u884ctruncate\uff1b\u8fd9\u662f\u4e3a\u4e86\u4fdd\u8bc1\u5728truncate\u4e2d\u95f4\u53d1\u751f\u91cd\u542f\u65f6\u53ef\u4ee5\u987a\u5229\u91cd\u5efa\u6b64undo tablespace\u3002\u901a\u8fc7trx_undo_truncate_tablespace()\u63a5\u53e3\u6765\u5bf9\u5176\u6587\u4ef6\u505a\u771f\u6b63\u7684truncate\u3002\u5220\u9664undo_trunc.log\u6807\u8bb0\u6587\u4ef6\uff0c\u8868\u660eundo tablespace\u7684truncate\u5df2\u7ecf\u5b8c\u6210\u3002\u6ce8\u610f\uff1a\u5f53\u4e00\u4e2aundo tablespace\u88ab\u6807\u8bb0\u4e3a\u9700\u8981truncate\u65f6\uff0c\u4e0d\u4f1a\u518d\u6709\u4e8b\u52a1\u4ece\u6b64undo tablespace\u5206\u914d\u56de\u6eda\u6bb5\uff0c\u800c\u4e14\u8fdb\u884ctruncate\u65f6\u5fc5\u987b\u4fdd\u8bc1\u8be5undo tablespace\u4e0a\u6240\u6709\u7684undo log\u90fd\u5df2\u7ecf\u88abpurge\u30024. \u6700\u540e\u901a\u8fc7\u4e0a\u9762\u7684\u4ecb\u7ecd\uff0c\u6211\u4eec\u77e5\u9053\u4e86undo log\u90a3\u4e9b\u8bb0\u5f55\u53ef\u4ee5\u88ab\u6e05\u7406\u4ee5\u53ca\u662f\u600e\u4e48\u6e05\u7406\u7684\uff0c\u4f46\u662f\u6e05\u7406undo log\u8fc7\u7a0b\u4e2d\u8fd8\u6709\u5f88\u591a\u7e41\u6742\u7684\u7ec6\u8282\uff1b\u6bd4\u5982\u6e05\u7406\u7d22\u5f15\u65f6\u6d89\u53ca\u5230\u5bf9B\u6811\u7684\u64cd\u4f5c\uff0c\u4ee5\u53ca\u65e7\u7248\u672c\u6570\u636e\u7684\u6784\u5efa\uff0cXA\u4e8b\u52a1\uff0cBLOB\u7b49\u7b49\uff1b\u8fd9\u7c7b\u5185\u5bb9\u6682\u65f6\u7565\u8fc7\u540e\u9762\u6709\u673a\u4f1a\u7ee7\u7eed\u4ecb\u7ecd\u3002\u53c2\u8003\u5185\u5bb9MySQL 8.0.23&#8217;s source codeMySQL 8.0 Reference ManualMySQL Server Team Blog\u5e96\u4e01\u89e3InnoDB\u4e4bUndo LOG\u6570\u636e\u5e93\u6545\u969c\u6062\u590d\u673a\u5236\u7684\u524d\u4e16\u4eca\u751f\u6d45\u6790\u6570\u636e\u5e93\u5e76\u53d1\u63a7\u5236\u673a\u5236Jeremy Cole&#8217;s github\u00a0A little fun with InnoDB multi-versioningThe basics of the InnoDB undo logging and history systemMySQL \u00b7 \u5f15\u64ce\u7279\u6027 \u00b7 InnoDB undo log \u6f2b\u6e38InnoDB\uff1aundo log\uff081\uff09InnoDB\uff1aundo log\uff082\uff09\u00a0\u539f\u6587\u94fe\u63a5\uff1a<a href=\"https:\/\/link.segmentfault.com\/?enc=JTtoASXYAh0%2Boj06jCSOLg%3D%3D.67s5EzrjCmvFWxTpJzjiHbsfZTcowGk8SXBQsmQq81d%2BzSeUmiMdcH56V3OJTDG8\" rel=\"nofollow\">http:\/\/click.aliyun.com\/m\/100&#8230;<\/a>\u672c\u6587\u4e3a\u963f\u91cc\u4e91\u539f\u521b\u5185\u5bb9\uff0c\u672a\u7ecf\u5141\u8bb8\u4e0d\u5f97\u8f6c\u8f7d\u3002<\/p>\n<p><a href=\"https:\/\/segmentfault.com\/a\/1190000042209801\">https:\/\/segmentfault.com\/a\/1190000042209801<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u7b80\u4ecb\uff1a\u00a0undo log\u662fInnoDB\u4e8b\u52a1\u7279\u6027\u7684\u91cd\u8981\u7ec4\u6210\u90e8\u5206\u3002\u5f53\u5bf9\u8bb0\u5f55\u505a\u589e\u5220\u6539\u64cd\u4f5c\u5c31\u4f1a\u4ea7\u751fundo\u8bb0\u5f55\uff0cund [&hellip;]<\/p>\n","protected":false},"author":0,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[],"tags":[],"class_list":["post-10005999","post","type-post","status-publish","format-standard","hentry"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/itmax.cn\/index.php?rest_route=\/wp\/v2\/posts\/10005999","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/itmax.cn\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/itmax.cn\/index.php?rest_route=\/wp\/v2\/types\/post"}],"replies":[{"embeddable":true,"href":"https:\/\/itmax.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=10005999"}],"version-history":[{"count":0,"href":"https:\/\/itmax.cn\/index.php?rest_route=\/wp\/v2\/posts\/10005999\/revisions"}],"wp:attachment":[{"href":"https:\/\/itmax.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=10005999"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/itmax.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=10005999"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/itmax.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=10005999"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}