用python在開發一個小web站點時碰到一個問題，通過mysql客戶端修改庫中數據后(有做提交)，在前臺web頁面刷新還是以前的數據。而另開一個mysql客戶端查詢是可以查詢到值的。重啟web服務后可以看到新值。而同樣使用java的jdbc方式連接時同樣的方式是可以看到新值的。

于是決定開啟mysql的日志看看實際運行的SQL有什么差異.

先看python連接方式的：

150517?13:34:00?????3?Connect???root@localhost?on?dw

3?Query?????SET?NAMES?'utf8'?COLLATE?'utf8_general_ci'

3?Query?????SET?@@session.autocommit?=?OFF

3?Query?????select?id,name?from?job?where?id=5

150517?13:34:20?????3?Query?????select?id,name?from?job?where?id=5

3?Quit

再來看看java的：

150517?13:39:08?????5?Connect???root@localhost?on?dw

5?Query?????/*?mysql-connector-java-5.1.25?(?Revision:?${bzr.revision-id}?)?*/SHOW?VARIABLES?WHERE?Variable_name?='language'?OR?Variable_name?=?'ne

t_write_timeout'?OR?Variable_name?=?'interactive_timeout'?OR?Variable_name?=?'wait_timeout'?OR?Variable_name?=?'character_set_client'?OR?Variable_name?=?'character_set

_connection'?OR?Variable_name?=?'character_set'?OR?Variable_name?=?'character_set_server'?OR?Variable_name?=?'tx_isolation'?OR?Variable_name?=?'transaction_isolation'

OR?Variable_name?=?'character_set_results'?OR?Variable_name?=?'timezone'?OR?Variable_name?=?'time_zone'?OR?Variable_name?=?'system_time_zone'?OR?Variable_name?=?'lower

_case_table_names'?OR?Variable_name?=?'max_allowed_packet'?OR?Variable_name?=?'net_buffer_length'?OR?Variable_name?=?'sql_mode'?OR?Variable_name?=?'query_cache_type'?O

R?Variable_name?=?'query_cache_size'?OR?Variable_name?=?'init_connect'

5?Query?????/*?mysql-connector-java-5.1.25?(?Revision:?${bzr.revision-id}?)?*/SELECT?@@session.auto_increment_increment

5?Query?????SHOW?COLLATION

5?Query?????SET?NAMES?latin1

5?Query?????SET?character_set_results?=?NULL

5?Query?????SET?autocommit=1

150517?13:39:09?????5?Query?????select?id,name?from?job?where?id=5

150517?13:39:29?????5?Query?????select?id,name?from?job?where?id=5

5?Quit

乍一看上去覺得差不多，沒什么差異。很是苦悶，于是再想另外的方法。啟動2個python腳本來嘗試，一個寫，另一個讀。

結果發現讀的那個腳本可以馬上讀到新增的數據。于是對比了下讀的腳本發現每次讀完后有做commit。把commit去掉再試，問題重現。再回過頭去看了下python腳本和java腳本生成的mysql日志的差異。發現

python:

3?Query?????SET?@@session.autocommit?=?OFF

java:

5?Query?????SET?autocommit=1

查詢mysql的文檔

The autocommit mode. If set to 1, all changes to a table take effect immediately. If set to 0, you must useCOMMITto accept a transaction orROLLBACKto cancel it

autocommit=1時為自動提交即autocommit=ON.

接下來嘗試了下postgresql，在autocommit=False時是可以查看到新數據的。

在看postgresql的python驅動的文檔時發現有個不錯的提示，轉帖如下：

Warning

By default, any query execution, including a simple?SELECT?will start a transaction: for long-running programs, if no further action is taken, the session will remain “idle in transaction”, a condition non desiderable for several reasons (locks are held by the session, tables bloat...). For long lived scripts, either ensure to terminate a transaction as soon as possible or use an autocommit connection.

總結

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