關(guān)于mysqldump，這個(gè)參數(shù)你可能還不知道
在前面文章中，有提到過 mysqldump 備份文件中記錄的時(shí)間戳數(shù)據(jù)都是以 UTC 時(shí)區(qū)為基礎(chǔ)的，在篩選恢復(fù)單庫或單表時(shí)要注意時(shí)區(qū)差別。后來再次查看文檔，發(fā)現(xiàn) tz-utc、skip-tz-utc 參數(shù)與此有關(guān)，本篇文章我們一起來看下此參數(shù)的作用吧。
? ?1.tz-utc與skip-tz-utc參數(shù)介紹
這兩個(gè)參數(shù)可以作用于 mysqldump 備份過程中，互為相反參數(shù)。顧名思義可以看出，一個(gè)參數(shù)是將時(shí)間戳改為 UTC 時(shí)區(qū)，另一個(gè)是跳過時(shí)區(qū)變動。
在 mysql 服務(wù)器上執(zhí)行 mysqldump --help 的命令，可以看到下面一段話。
[root@host?~]#?mysqldump?--help
mysqldump??Ver?10.13?Distrib?5.7.23,?for?Linux?(x86_64)
Copyright?(c)?2000,?2018,?Oracle?and/or?its?affiliates.?All?rights?reserved.
...省略很多內(nèi)容
??--tz-utc????????????SET?TIME_ZONE='+00:00'?at?top?of?dump?to?allow?dumping?of
??????????????????????TIMESTAMP?data?when?a?server?has?data?in?different?time
??????????????????????zones?or?data?is?being?moved?between?servers?with
??????????????????????different?time?zones.
??????????????????????(Defaults?to?on;?use?--skip-tz-utc?to?disable.)--tz-utc 參數(shù)是 mysqldump 的默認(rèn)參數(shù)，會使得 mysqldump 的導(dǎo)出文件的頂部加上一個(gè)設(shè)置時(shí)區(qū)的語句 SET TIME_ZONE='+00:00' ，這個(gè)時(shí)區(qū)是格林威治時(shí)間，也就是0時(shí)區(qū)。這樣當(dāng)導(dǎo)出 timestamp 時(shí)間戳字段時(shí)，會把在服務(wù)器設(shè)置的當(dāng)前時(shí)區(qū)下顯示的 timestamp 時(shí)間值轉(zhuǎn)化為在格林威治時(shí)間下顯示的時(shí)間。比如我們數(shù)據(jù)庫采用北京時(shí)間東八區(qū)，mysqldump 導(dǎo)出的文件當(dāng)中顯示的 timestamp 時(shí)間值相對于通過數(shù)據(jù)庫查詢顯示的時(shí)間倒退了8個(gè)小時(shí)。
知道了 --tz-utc ，那么 --skip-tz-utc 的含義就是當(dāng) mysqldump 導(dǎo)出數(shù)據(jù)時(shí)，不使用格林威治時(shí)間，而使用當(dāng)前 mysql 服務(wù)器的時(shí)區(qū)進(jìn)行導(dǎo)出，這樣導(dǎo)出的數(shù)據(jù)中顯示的 timestamp 時(shí)間值也和表中查詢出來的時(shí)間值相同。
? ?2.實(shí)驗(yàn)參數(shù)具體作用
為了更清楚了解這對參數(shù)的作用，下面我們來具體測試下，我們知道 mysqldump 后可以跟 where 條件來備份部分?jǐn)?shù)據(jù)，若根據(jù) timestamp 字段來備份部分?jǐn)?shù)據(jù)，這對參數(shù)是否有影響呢？我們一并來驗(yàn)證下：
先來看下我的環(huán)境設(shè)置及測試數(shù)據(jù)：
mysql>?select?version();
+------------+
|?version()??|
+------------+
|?5.7.23-log?|
+------------+
1?row?in?set?(0.00?sec)
#?時(shí)區(qū)采用北京時(shí)間東八區(qū)
mysql>?show?variables?like?'time_zone';?
+---------------+--------+
|?Variable_name?|?Value??|
+---------------+--------+
|?time_zone?????|?+08:00?|
+---------------+--------+
1?row?in?set?(0.00?sec)
#?測試表?有datetime字段和timestamp字段?共10條數(shù)據(jù)?兩個(gè)時(shí)間顯示是相同的
mysql>?show?create?table?test_tb\G
***************************?1.?row?***************************
???????Table:?test_tb
Create?Table:?CREATE?TABLE?`test_tb`?(
??`increment_id`?int(11)?NOT?NULL?AUTO_INCREMENT?COMMENT?'自增主鍵',
??`stu_id`?int(11)?NOT?NULL?COMMENT?'學(xué)號',
??`stu_name`?varchar(20)?DEFAULT?NULL?COMMENT?'學(xué)生姓名',
??`dt_time`?datetime?NOT?NULL,
??`create_time`?timestamp?NOT?NULL?DEFAULT?CURRENT_TIMESTAMP?COMMENT?'創(chuàng)建時(shí)間',
??PRIMARY?KEY?(`increment_id`)
)?ENGINE=InnoDB?AUTO_INCREMENT=11?DEFAULT?CHARSET=utf8?COMMENT='測試表'
1?row?in?set?(0.00?sec)
mysql>?select?*?from?test_tb;
+--------------+--------+----------+---------------------+---------------------+
|?increment_id?|?stu_id?|?stu_name?|?dt_time?????????????|?create_time?????????|
+--------------+--------+----------+---------------------+---------------------+
|????????????1?|???1001?|?fgds?????|?2020-07-10?09:43:28?|?2020-07-10?09:43:28?|
|????????????2?|???1002?|?fgsw?????|?2020-10-10?09:43:28?|?2020-10-10?09:43:28?|
|????????????3?|???1003?|?vffg?????|?2020-10-10?02:00:00?|?2020-10-10?02:00:00?|
|????????????4?|???1004?|?wdsd?????|?2020-10-31?23:43:28?|?2020-10-31?23:43:28?|
|????????????5?|???1005?|?grdb?????|?2020-11-01?00:00:00?|?2020-11-01?00:00:00?|
|????????????6?|???1006?|?sdfv?????|?2020-11-01?02:00:00?|?2020-11-01?02:00:00?|
|????????????7?|???1007?|?fgfg?????|?2020-11-06?02:00:00?|?2020-11-06?02:00:00?|
|????????????8?|???1008?|?tyth?????|?2020-11-10?09:43:28?|?2020-11-10?09:43:28?|
|????????????9?|???1009?|?ewer?????|?2020-11-10?09:43:28?|?2020-11-10?09:43:28?|
|???????????10?|???1010?|?erre?????|?2020-11-11?15:17:03?|?2020-11-11?15:17:03?|
+--------------+--------+----------+---------------------+---------------------+mysqldump 默認(rèn)開啟 tz-utc ，先來看下默認(rèn)情況下的備份結(jié)果：
#?為更明顯看出結(jié)果?我們使用skip-extended-insert來一行行展現(xiàn)數(shù)據(jù)
#?全庫備份
[root@host?~]#?mysqldump?-uroot?-pxxxx??--skip-extended-insert?--databases?testdb?>?utc_testdb.sql
mysqldump:?[Warning]?Using?a?password?on?the?command?line?interface?can?be?insecure.
[root@host?~]#?more?utc_testdb.sql?
--?MySQL?dump?10.13??Distrib?5.7.23,?for?Linux?(x86_64)
--
--?Host:?localhost????Database:?testdb
--?------------------------------------------------------
--?Server?version???????5.7.23-log
...省略
/*!40103?SET?@OLD_TIME_ZONE=@@TIME_ZONE?*/;
/*!40103?SET?TIME_ZONE='+00:00'?*/;
#?先保存老時(shí)區(qū)?然后將此會話時(shí)區(qū)改為0時(shí)區(qū)
...省略
--
--?Dumping?data?for?table?`test_tb`
--
LOCK?TABLES?`test_tb`?WRITE;
/*!40000?ALTER?TABLE?`test_tb`?DISABLE?KEYS?*/;
INSERT?INTO?`test_tb`?VALUES?(1,1001,'fgds','2020-07-10?09:43:28','2020-07-10?01:43:28');
INSERT?INTO?`test_tb`?VALUES?(2,1002,'fgsw','2020-10-10?09:43:28','2020-10-10?01:43:28');
INSERT?INTO?`test_tb`?VALUES?(3,1003,'vffg','2020-10-10?02:00:00','2020-10-09?18:00:00');
INSERT?INTO?`test_tb`?VALUES?(4,1004,'wdsd','2020-10-31?23:43:28','2020-10-31?15:43:28');
INSERT?INTO?`test_tb`?VALUES?(5,1005,'grdb','2020-11-01?00:00:00','2020-10-31?16:00:00');
INSERT?INTO?`test_tb`?VALUES?(6,1006,'sdfv','2020-11-01?02:00:00','2020-10-31?18:00:00');
INSERT?INTO?`test_tb`?VALUES?(7,1007,'fgfg','2020-11-06?02:00:00','2020-11-05?18:00:00');
INSERT?INTO?`test_tb`?VALUES?(8,1008,'tyth','2020-11-10?09:43:28','2020-11-10?01:43:28');
INSERT?INTO?`test_tb`?VALUES?(9,1009,'ewer','2020-11-10?09:43:28','2020-11-10?01:43:28');
INSERT?INTO?`test_tb`?VALUES?(10,1010,'erre','2020-11-11?15:17:03','2020-11-11?07:17:03');
#?可以看出timestamp時(shí)間值減去了8小時(shí)?而datetime時(shí)間值不變
UNLOCK?TABLES;
/*!40103?SET?TIME_ZONE=@OLD_TIME_ZONE?*/;
#?再將時(shí)區(qū)改為原時(shí)區(qū)
/*!40101?SET?SQL_MODE=@OLD_SQL_MODE?*/;
--?Dump?completed?on?2020-11-11?15:34:21
#?使用where條件備份單表部分?jǐn)?shù)據(jù)?備份11月份以來的數(shù)據(jù)
#?數(shù)據(jù)庫中查詢
mysql>?select?*?from?test_tb?where?create_time?>=?'2020-11-01?00:00:00';
+--------------+--------+----------+---------------------+---------------------+
|?increment_id?|?stu_id?|?stu_name?|?dt_time?????????????|?create_time?????????|
+--------------+--------+----------+---------------------+---------------------+
|????????????5?|???1005?|?grdb?????|?2020-11-01?00:00:00?|?2020-11-01?00:00:00?|
|????????????6?|???1006?|?sdfv?????|?2020-11-01?02:00:00?|?2020-11-01?02:00:00?|
|????????????7?|???1007?|?fgfg?????|?2020-11-06?02:00:00?|?2020-11-06?02:00:00?|
|????????????8?|???1008?|?tyth?????|?2020-11-10?09:43:28?|?2020-11-10?09:43:28?|
|????????????9?|???1009?|?ewer?????|?2020-11-10?09:43:28?|?2020-11-10?09:43:28?|
|???????????10?|???1010?|?erre?????|?2020-11-11?15:17:03?|?2020-11-11?15:17:03?|
+--------------+--------+----------+---------------------+---------------------+
6?rows?in?set?(0.00?sec)
#?mysqldump導(dǎo)出
[root@host?~]#?mysqldump?-uroot?-pxxxx??--skip-extended-insert?testdb?test_tb?--where?"create_time?>=?'2020-11-01?00:00:00'?"?>?utc_testdb2.sql
mysqldump:?[Warning]?Using?a?password?on?the?command?line?interface?can?be?insecure.
[root@host?~]#?more?utc_testdb2.sql?
--?MySQL?dump?10.13??Distrib?5.7.23,?for?Linux?(x86_64)
--
--?Host:?localhost????Database:?testdb
--?------------------------------------------------------
--?Server?version???????5.7.23-log
...
/*!40103?SET?@OLD_TIME_ZONE=@@TIME_ZONE?*/;
/*!40103?SET?TIME_ZONE='+00:00'?*/;
...省略
--
--?Dumping?data?for?table?`test_tb`
--
--?WHERE:??create_time?>=?'2020-11-01?00:00:00'?
LOCK?TABLES?`test_tb`?WRITE;
/*!40000?ALTER?TABLE?`test_tb`?DISABLE?KEYS?*/;
INSERT?INTO?`test_tb`?VALUES?(7,1007,'fgfg','2020-11-06?02:00:00','2020-11-05?18:00:00');
INSERT?INTO?`test_tb`?VALUES?(8,1008,'tyth','2020-11-10?09:43:28','2020-11-10?01:43:28');
INSERT?INTO?`test_tb`?VALUES?(9,1009,'ewer','2020-11-10?09:43:28','2020-11-10?01:43:28');
INSERT?INTO?`test_tb`?VALUES?(10,1010,'erre','2020-11-11?15:17:03','2020-11-11?07:17:03');
#?發(fā)現(xiàn)只導(dǎo)出4條
UNLOCK?TABLES;
/*!40103?SET?TIME_ZONE=@OLD_TIME_ZONE?*/;
--?Dump?completed?on?2020-11-11?15:58:56建議各位仔細(xì)看下上面導(dǎo)出結(jié)果，說實(shí)話，筆者原來也沒做過詳細(xì)測試，現(xiàn)在看到結(jié)果也是稍微有點(diǎn)吃驚的。默認(rèn)情況下，全備出來的數(shù)據(jù)是沒問題的，雖然將 timestamp 時(shí)間值轉(zhuǎn)為0時(shí)區(qū)顯示，但當(dāng)你導(dǎo)入數(shù)據(jù)庫時(shí)還會以你的數(shù)據(jù)庫時(shí)區(qū)來展示 timestamp 時(shí)間。但使用 where 條件導(dǎo)出部分?jǐn)?shù)據(jù)時(shí)，卻出現(xiàn)了數(shù)據(jù)庫中查詢得出的結(jié)果與dump導(dǎo)出的結(jié)果不同的情況，這個(gè)時(shí)候 mysqldump 只導(dǎo)出了轉(zhuǎn)化成0時(shí)區(qū)后的時(shí)間值符合 where 條件的數(shù)據(jù)，與直接查詢出的結(jié)果有出入，這是我原來沒注意到的。
再來看下使用 --skip-tz-utc 參數(shù)，看下這個(gè)參數(shù)是否符合我們的預(yù)期：
#?使用skip-tz-utc全備
[root@host?~]#?mysqldump?-uroot?-pxxxx??--skip-extended-insert?--skip-tz-utc?--databases?testdb?>?skiputc_testdb.sql
mysqldump:?[Warning]?Using?a?password?on?the?command?line?interface?can?be?insecure.
[root@host?~]#?more?skiputc_testdb.sql?
--?MySQL?dump?10.13??Distrib?5.7.23,?for?Linux?(x86_64)
--
--?Host:?localhost????Database:?testdb
--?------------------------------------------------------
--?Server?version???????5.7.23-log
..省略?未見時(shí)區(qū)更改語句
--
--?Dumping?data?for?table?`test_tb`
--
LOCK?TABLES?`test_tb`?WRITE;
/*!40000?ALTER?TABLE?`test_tb`?DISABLE?KEYS?*/;
INSERT?INTO?`test_tb`?VALUES?(1,1001,'fgds','2020-07-10?09:43:28','2020-07-10?09:43:28');
INSERT?INTO?`test_tb`?VALUES?(2,1002,'fgsw','2020-10-10?09:43:28','2020-10-10?09:43:28');
INSERT?INTO?`test_tb`?VALUES?(3,1003,'vffg','2020-10-10?02:00:00','2020-10-10?02:00:00');
INSERT?INTO?`test_tb`?VALUES?(4,1004,'wdsd','2020-10-31?23:43:28','2020-10-31?23:43:28');
INSERT?INTO?`test_tb`?VALUES?(5,1005,'grdb','2020-11-01?00:00:00','2020-11-01?00:00:00');
INSERT?INTO?`test_tb`?VALUES?(6,1006,'sdfv','2020-11-01?02:00:00','2020-11-01?02:00:00');
INSERT?INTO?`test_tb`?VALUES?(7,1007,'fgfg','2020-11-06?02:00:00','2020-11-06?02:00:00');
INSERT?INTO?`test_tb`?VALUES?(8,1008,'tyth','2020-11-10?09:43:28','2020-11-10?09:43:28');
INSERT?INTO?`test_tb`?VALUES?(9,1009,'ewer','2020-11-10?09:43:28','2020-11-10?09:43:28');
INSERT?INTO?`test_tb`?VALUES?(10,1010,'erre','2020-11-11?15:17:03','2020-11-11?15:17:03');
#?timestamp時(shí)間值顯示與datetime顯示一樣?未做轉(zhuǎn)換
UNLOCK?TABLES;
--?Dump?completed?on?2020-11-11?16:23:32
#?使用skip-tz-utc備份部分?jǐn)?shù)據(jù)
[root@host?~]#?mysqldump?-uroot?-pxxxx??--skip-extended-insert?--skip-tz-utc?testdb?test_tb?--where?"create_time?>=?'2020-11-01?00:00:00'?"?>?skiputc_testdb2.sql
mysqldump:?[Warning]?Using?a?password?on?the?command?line?interface?can?be?insecure.
[root@host?~]#?more?skiputc_testdb2.sql?
--?MySQL?dump?10.13??Distrib?5.7.23,?for?Linux?(x86_64)
--
--?Host:?localhost????Database:?testdb
--?------------------------------------------------------
--?Server?version???????5.7.23-log
..?省略
--
--?Dumping?data?for?table?`test_tb`
--
--?WHERE:??create_time?>=?'2020-11-01?00:00:00'?
LOCK?TABLES?`test_tb`?WRITE;
/*!40000?ALTER?TABLE?`test_tb`?DISABLE?KEYS?*/;
INSERT?INTO?`test_tb`?VALUES?(5,1005,'grdb','2020-11-01?00:00:00','2020-11-01?00:00:00');
INSERT?INTO?`test_tb`?VALUES?(6,1006,'sdfv','2020-11-01?02:00:00','2020-11-01?02:00:00');
INSERT?INTO?`test_tb`?VALUES?(7,1007,'fgfg','2020-11-06?02:00:00','2020-11-06?02:00:00');
INSERT?INTO?`test_tb`?VALUES?(8,1008,'tyth','2020-11-10?09:43:28','2020-11-10?09:43:28');
INSERT?INTO?`test_tb`?VALUES?(9,1009,'ewer','2020-11-10?09:43:28','2020-11-10?09:43:28');
INSERT?INTO?`test_tb`?VALUES?(10,1010,'erre','2020-11-11?15:17:03','2020-11-11?15:17:03');
#?6條數(shù)據(jù)?和數(shù)據(jù)庫中查詢一致
UNLOCK?TABLES;
--?Dump?completed?on?2020-11-11?16:28:39從上面結(jié)果可以看出，使用 --skip-tz-utc 參數(shù)后，timestamp 時(shí)間戳字段值不會轉(zhuǎn)換，導(dǎo)出部分?jǐn)?shù)據(jù)也符合預(yù)期。
? ?3.一些小建議
那么這個(gè)參數(shù)的意義何在呢？當(dāng)你的數(shù)據(jù)庫服務(wù)器處于不同時(shí)區(qū)時(shí)。假設(shè)一個(gè)服務(wù)器在北京（東八區(qū)），一個(gè)服務(wù)器在東京（東九區(qū)），現(xiàn)在需要將北京服務(wù)器里的數(shù)據(jù)導(dǎo)入至東京服務(wù)器。當(dāng)導(dǎo)入按照默認(rèn)不加 --skip-tz-utc 參數(shù)的dump文件，查詢的 timestamp 時(shí)間數(shù)據(jù)相對于在之前的東八區(qū)服務(wù)器的時(shí)間值多了一個(gè)小時(shí)，但由于東八區(qū)服務(wù)器里的13點(diǎn)和東九區(qū)服務(wù)器里的14點(diǎn)代表的是同一時(shí)刻，所以，在東九區(qū)的服務(wù)器里顯示的多出的一個(gè)小時(shí)，這樣顯示是正確的。而如果增加 --skip-tz-utc 參數(shù)，dump文件導(dǎo)入東九區(qū)服務(wù)器后，盡管顯示的時(shí)間值和之前東八區(qū)服務(wù)器顯示的時(shí)間值相同，但兩者代表的時(shí)刻卻已經(jīng)不同。
關(guān)于這個(gè)參數(shù)應(yīng)該如何使用，我們首先應(yīng)該明白，是否加上 --skip-tz-utc 參數(shù)，只會影響 timestamp 字段的導(dǎo)入導(dǎo)出，對 datetime 時(shí)間字段不會影響。
這里筆者建議首先對 timestamp 字段使用作出規(guī)范。比如 timestamp 字段只用于創(chuàng)建時(shí)間和更新時(shí)間需求，只代表該行數(shù)據(jù)的創(chuàng)建及更新時(shí)間，做到與業(yè)務(wù)弱相關(guān)，其他時(shí)間字段盡量使用 datetime 。這樣即使 mysqldump 采用不同參數(shù)，實(shí)際產(chǎn)生影響也不大。
如果你的服務(wù)器處于不同時(shí)區(qū)，那建議還是按照默認(rèn)來，這樣導(dǎo)入導(dǎo)出的數(shù)據(jù)都是正確的。如果你的服務(wù)器都是處于同一時(shí)區(qū)，那么是否使用 --skip-tz-utc 參數(shù)區(qū)別不大，我們只需知道默認(rèn)情況 mysqldump 會將 timestamp 時(shí)間值轉(zhuǎn)為0時(shí)區(qū)存儲即可。當(dāng)備份部分?jǐn)?shù)據(jù)且以 timestamp 字段來篩選時(shí)，這時(shí)候建議增加 --skip-tz-utc 參數(shù)。這里再次提醒下，從全備中篩選單庫或單表的備份時(shí)，也要注意下 timestamp 字段數(shù)據(jù)。
參考：?
https://zhuanlan.zhihu.com/p/99395517
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