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mysql的XA事務(wù)恢復(fù)過程詳解

更新時間：2012年11月13日 10:21:46 作者：

XA事務(wù)支持限于InnoDB存儲引擎,本文將詳細(xì)介紹mysql的XA事務(wù)恢復(fù)過程

mysql數(shù)據(jù)庫開機(jī)報錯：
InnoDB: The log sequence number in ibdata files does not match
InnoDB: the log sequence number in the ib_logfiles!
100224 12:24:20 InnoDB: Database was not shut down normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files...
InnoDB: Restoring possible half-written data pages from the doublewrite
InnoDB: buffer...
InnoDB: Transaction 0 4497755 was in the XA prepared state.
InnoDB: Transaction 0 4468551 was in the XA prepared state.
InnoDB: Transaction 0 4468140 was in the XA prepared state.
InnoDB: 3 transaction(s) which must be rolled back or cleaned up
InnoDB: in total 0 row operations to undo
InnoDB: Trx id counter is 0 5312768
InnoDB: Starting in background the rollback of uncommitted transactions
100224 12:24:20 InnoDB: Rollback of non-prepared transactions completed
100224 12:24:20 InnoDB: Started; log sequence number 0 3805002509
100224 12:24:20 InnoDB: Starting recovery for XA transactions...
100224 12:24:20 InnoDB: Transaction 0 4497755 in prepared state after recovery
100224 12:24:20 InnoDB: Transaction contains changes to 8 rows
100224 12:24:20 InnoDB: Transaction 0 4468551 in prepared state after recovery
100224 12:24:20 InnoDB: Transaction contains changes to 1 rows
100224 12:24:20 InnoDB: Transaction 0 4468140 in prepared state after recovery
100224 12:24:20 InnoDB: Transaction contains changes to 1 rows
100224 12:24:20 InnoDB: 3 transactions in prepared state after recovery
100224 12:24:20 [Note] Found 3 prepared transaction(s) in InnoDB
100224 12:24:20 [Warning] Found 3 prepared XA transactions
100224 12:24:20 [Note] Event Scheduler: Loaded 0 events
100224 12:24:20 [Note] /opt/mysql/bin/mysqld: ready for connections.
Version: '5.1.39' socket: '/tmp/mysql.sock' port: 3306 MySQL Community Server (GPL)
意味著有三個XA的事務(wù)沒有提交或回滾。
登錄到mysql
mysql> xa recover;
+----------+--------------+--------------+------------------------------------------------------------+
| formatID | gtrid_length | bqual_length | data |
+----------+--------------+--------------+------------------------------------------------------------+
| 131075 | 30 | 28 | 1-7f000001:bae5:4b6928eb:f06397f000001:bae5:4b6928eb:f0650 |
| 131075 | 30 | 28 | 1-7f000001:bae5:4b6928eb:fb5c37f000001:bae5:4b6928eb:fb5cd |
| 131075 | 30 | 28 | 1-7f000001:bae5:4b6928eb:f03ea7f000001:bae5:4b6928eb:f0400 |
+----------+--------------+--------------+------------------------------------------------------------+
數(shù)據(jù)表示信息如下：
formatIDis the formatIDpart of the transaction xid
gtrid_lengthis the length in bytes of the gtridpart of the xid
bqual_lengthis the length in bytes of the bqualpart of the xid
datais the concatenation of the gtridand bqualparts of the xid
這是三個XA事務(wù)的信息，準(zhǔn)備直接回滾。
mysql> xa rollback '1-7f000001:bae5:4b6928eb:fb5c3','7f000001:bae5:4b6928eb:fb5cd',131075;
Query OK, 0 rows affected (0.41 sec)
再啟動就正常了。

MySQL XA
I.5. 對XA事務(wù)的限制
XA事務(wù)支持限于InnoDB存儲引擎。
MySQL XA實(shí)施是針對外部XA的，其中，MySQL服務(wù)器作為資源管理器，而客戶端程序作為事務(wù)管理器。未實(shí)施“內(nèi)部XA”。這樣，就允許MySQL服務(wù)器內(nèi)的單獨(dú)存儲引擎作為RM（資源管理器），而服務(wù)器本身作為TM（事務(wù)管理器）。處理包含1個以上存儲引擎的XA事務(wù)時，需要內(nèi)部XA。內(nèi)部XA的實(shí)施是不完整的，這是因?yàn)?，它要求存儲引擎在表處理程序?qū)用嫔现С謨呻A段提交，目前僅對InnoDB實(shí)現(xiàn)了該特性。
對于XA START，不支持JOIN和RESUME子句。

對于XA END，不支持SUSPEND [FOR MIGRATE]子句。
在全局事務(wù)內(nèi)，對于每個XA事務(wù)，xid值的bqual部分應(yīng)是不同的，該要求是對當(dāng)前MySQL XA實(shí)施的限制。它不是XA規(guī)范的組成部分。

如果XA事務(wù)達(dá)到PREPARED狀態(tài)而且MySQL服務(wù)器宕機(jī)，當(dāng)服務(wù)器重啟后，能夠繼續(xù)處理事務(wù)。就像原本應(yīng)當(dāng)?shù)哪菢印５?，如果客戶端連接中止而服務(wù)器繼續(xù)運(yùn)行，服務(wù)器將回滾任何未完成的XA事務(wù)，即使該事務(wù)已達(dá)到PREPARED狀態(tài)也同樣。它應(yīng)能提交或回滾PREPARED XA事務(wù)，但在不更改二進(jìn)制日志機(jī)制的情況下不能這樣。

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