MySQL myisamchk修復爛掉的table

轉載自 Zaw Min Blog

MyISAM是MySQL的預設storage engine. MyISAM table很容易爛掉(corrupted)。
此文章將教你如何檢查/修復這些爛掉的MyISAM tables.

每次你在MySQL DB 製造一個 table，將會在檔案系統上同時製造出*.frm、*.MYD，跟*.MYI等三種格式的檔案。

*.frm = 用來儲存資料表格式(file to store table format)
*.MYD(MyData) = 用來儲存資料(file to store data)
*.MYI(MyIndex) =用來儲存索引(file to store index)

如何檢查DB裡哪個table 需要修復：

用root 執行以下指令，假設要檢查DB1下的各個table

1	#myisamchk /var/lib/mysql/DB1/*.MYI >> /tmp/myisamchk.log

螢幕輸出中，如果發現以下字樣，該資料表就應修復

myisamchk: error: Keypointers and record positions doesn’t match
MyISAM-table ‘/var/lib/mysql/DB1/news_post_comment.MYI’ is corrupted
Fix it using switch “-r” or “-o”
myisamchk: warning: 1 client is using or hasn’t closed the table properly
MyISAM-table ‘/var/lib/mysql/DB1/news_post.MYI’ is usable but should be fixed
myisamchk: warning: 1 client is using or hasn’t closed the table properly
MyISAM-table ‘/var/lib/mysql/DB1/news_post_push_log.MYI’ is usable but should be fixed

Redirect出來的檔案中會顯示更多資訊。如下

Checking MyISAM file: /var/lib/mysql/DB1/yam_bbauth.MYI
Data records: 14 Deleted blocks: 0
– check file-size
– check record delete-chain
– check key delete-chain
– check index reference
– check data record references index: 1
– check record links

如何利用myisamchk修復爛掉的tables：

找出爛掉的table之後，用以下指令修復，

1	#myisamchk –r /var/lib/mysql/DB1/news_post_comment.MYI

– recovering (with sort) MyISAM-table ‘/var/lib/mysql/DB1/news_post_comment.MYI
Data records: 1
– Fixing index 1

如果table正被某個application使用，你可能會看到： clients are using or haven’t closed the table properly。
所以建議修復前將mysqld關掉或用FLUSH TABLES鎖住TABLES，防止修復時有application對DB TABLE做更動。

如何讓檢查跟修復同時進行：

1	#myisamchk --silent --force --fast --update-state /var/lib/mysql/DB1/*.MYI

myisamchk: MyISAM file /var/lib/mysql/DB1/groups.MYI
myisamchk: warning: 1 client is using or hasn’t closed the table properly
myisamchk: MyISAM file /var/lib/mysql/DB1/profiles.MYI
myisamchk: warning: 1 client is using or hasn’t closed the table properly

options 的意義如下：
• s, –silent option: Prints only errors. You can use two -s to make myisamchk very silent.
• -f, –force option: Restart myisamchk automatically with repair option -r, if there are any errors in the table.
• -F, –fast option: Check only tables that haven’t been closed properly.
• -U –update-state option: Marks tables as crashed, when it finds any error.

修復時手動分配記憶體給龐大的DB

龐大的table，修復需要很長的時間。修復時可以手動增加記憶體參數。

1 2	# myisamchk --silent --force --fast --update-state --key_buffer_size=512M --sort_buffer_size=512M \ --read_buffer_size=4M --write_buffer_size=4M /var/lib/mysql/DB1/*.MYI

用myisamchk 獲取table資訊

1	#myisamchk -dvv profiles.MYI

MyISAM file: profiles.MYI
Record format: Packed
Character set: latin1_swedish_ci (8)
File-version: 1
Creation time: 2007-08-16 18:46:59
Status: open,changed,analyzed,optimized keys,sorted index pages
Auto increment key: 1 Last value: 88
Data records: 88 Deleted blocks: 0
Datafile parts: 118 Deleted data: 0
Datafile pointer (bytes): 4 Keyfile pointer (bytes): 4
Datafile length: 6292 Keyfile length: 6144
Max datafile length: 4294967294 Max keyfile length: 4398046510079
Recordlength: 2124

table description:
Key Start Len Index Type Rec/key Root Blocksize
1 2 3 unique int24 1 1024 1024
2 5 765 unique char packed stripped 1 2048 4096

Field Start Length Nullpos Nullbit Type
1 1 1
2 2 3 no zeros
3 5 765 no endspace

最後一招

1	#myisamchk --help

Reference:http://www.thegeekstuff.com/2008/09/how-to-repair-corrupted-mysql-tables-using-myisamchk/