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這篇文章主要介紹“MySQL中begin后事務(wù)為什么不提交”,在日常操作中,相信很多人在MySQL中begin后事務(wù)為什么不提交問題上存在疑惑,小編查閱了各式資料,整理出簡單好用的操作方法,希望對大家解答”MySQL中begin后事務(wù)為什么不提交”的疑惑有所幫助!接下來,請跟著小編一起來學(xué)習(xí)吧!
今天順便看了一下,主要流程就是跟蹤為什么begin后事物不會(huì)提交,最后發(fā)現(xiàn)在:
MYSQL_BIN_LOG::commit 函數(shù)中包含這個(gè)判斷
if (!cache_mngr->trx_cache.is_binlog_empty() && ending_trans(thd, all) && !trx_stuff_logged)
如果begin的話ending_trans(thd, all) 將會(huì)返回為false,也就不會(huì)調(diào)用 order_commit流程了。
那么其主要判斷就是:
bool ending_single_stmt_trans(THD* thd, const bool all){ return (!all && !thd->in_multi_stmt_transaction_mode()); }
下面是源碼注釋和函數(shù):
Returns TRUE if session is in a multi-statement transaction mode. OPTION_NOT_AUTOCOMMIT: When autocommit is off, a multi-statement transaction is implicitly started on the first statement after a previous transaction has been ended. OPTION_BEGIN: Regardless of the autocommit status, a multi-statement transaction can be explicitly started with the statements "START TRANSACTION", "BEGIN [WORK]", "[COMMIT | ROLLBACK] AND CHAIN", etc. Note: this doesn't tell you whether a transaction is active. A session can be in multi-statement transaction mode, and yet have no active transaction, e.g., in case of: set @@autocommit=0; set @a= 3; <-- these statements don't set transaction isolation level serializable; <-- start an active flush tables; <-- transaction I.e. for the above scenario this function returns TRUE, even though no active transaction has begun. @sa in_active_multi_stmt_transaction() */ inline bool in_multi_stmt_transaction_mode() const { return variables.option_bits & (OPTION_NOT_AUTOCOMMIT | OPTION_BEGIN); }
其實(shí)就是在判斷是都o(jì)ption_bits的對應(yīng)位上為1。因此簡單了我們就看看什么時(shí)候設(shè)置OPTION_BEGIN位就好了。
實(shí)際上是函數(shù)trans_begin設(shè)置的下面是這段代碼:
thd->variables.option_bits|= OPTION_BEGIN; thd->server_status|= SERVER_STATUS_IN_TRANS; if (thd->tx_read_only) thd->server_status|= SERVER_STATUS_IN_TRANS_READONLY; DBUG_PRINT("info", ("setting SERVER_STATUS_IN_TRANS")); if (tst) tst->add_trx_state(thd, TX_EXPLICIT); /* ha_start_consistent_snapshot() relies on OPTION_BEGIN flag set. */ if (flags & MYSQL_START_TRANS_OPT_WITH_CONS_SNAPSHOT) { if (tst) tst->add_trx_state(thd, TX_WITH_SNAPSHOT); res= ha_start_consistent_snapshot(thd); }
實(shí)際上就是在MySQL層設(shè)置一些標(biāo)示,如果是 START TRANSACTION WITH CONSISTENT SNAPSHOT 還會(huì)開啟一個(gè)一致性快照,就是一個(gè)readview。一旦設(shè)置了個(gè)標(biāo)示將會(huì)不自動(dòng)提交了。
到此,關(guān)于“MySQL中begin后事務(wù)為什么不提交”的學(xué)習(xí)就結(jié)束了,希望能夠解決大家的疑惑。理論與實(shí)踐的搭配能更好的幫助大家學(xué)習(xí),快去試試吧!若想繼續(xù)學(xué)習(xí)更多相關(guān)知識,請繼續(xù)關(guān)注億速云網(wǎng)站,小編會(huì)繼續(xù)努力為大家?guī)砀鄬?shí)用的文章!
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