昨天由於機房掉電自己的mysql數據庫中大量表都出現了無法訪問或正使用的情況，後來查了可以使用mysql myisamchk命令進行修復，下面我來介紹一下。
Posted on December 31, 2009 by axl 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 制造一個 table，將會在檔案系統上同時制造出*.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?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
代碼如下 復制代碼 #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
代碼如下 復制代碼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，
代碼如下 復制代碼 #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：
代碼如下 復制代碼 #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。
代碼如下 復制代碼 # myisamchk --silent --force --fast --update-state --key_buffer_size=512M --sort_buffer_size=512M用myisamchk 獲取table資訊
1
代碼如下 復制代碼 #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
#myisamchk --help
MySQL 使用 myisamchk 修復 *.MYI 時, 出現下述訊息:
myisamchk: Disk is full writing '/tmp/ST3lJjsW' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to c ontinue after freeing disk space)
myisamchk: Retry in 60 secs. Message reprinted in 600 secs
解法1:
■由訊息可以知道, myisamchk 需要使用到 /tmp, /tmp 容量不夠就會出現此訊息, 所以如果 /tmp 可以清出空間, 清出 /tmp 的空間就可以解決了.
但是如果 /tmp 本身切的就不夠大, 可以使用下述解法.
解法2:
此解法取自: free disk space error using myisamchk
■myisamchk -rq --sort_buffer_size=256M --key_buffer_size=256M --read_buffer_size=32M --write_buffer_size=32M --sort-index --analyze --tmpdir=/more-disk-space-directory/ /var/lib/mysql/database/T1.MYI
■?: 修改 --tmpdir=/more-disk-space-directory/ 指定到空間比較大的地方去即可.
