7.12.2011

Diary of a mysql database problem in 15 minutes


1:42pm - frantic instant message comes in from a smallish project that their site is down.

1:42pm - I ssh into both the webserver and the database server.  Database server takes awhile to actually get a login prompt.

1:43pm - Email containing frantic instant message with importance set to high ( side note- people still use importance in emails? people still email after they've contacted you another way?  people still email? )

1:44pm - I run "top" on both the webserver and the database server.   ( There isn't any other monitoring since it's a smallish project.   there probably should be.  Will have to get client to pay for that.)  Webserver looks fine.  Database server load is really high, around 5 when it's usually around 0.30.  This is a mysql linux server.

1:45pm - exit "top" and open a mysql command line prompt.

1:46pm - execute "show processlist" in mysql.  A ton of queries show up, all behind one sinister looking one on a new table that's been set up recently.

1:47pm - execute "explain sinister-looking query" in mysql to see how mysql is executing that query.

1:48pm - possible_keys = NULL

1:49pm - Ruh roh.  Execute "alter table add index..."

1:50pm - database working.

1:51pm - database working.

1:52pm - database working.

1:53pm - database done working.  execute "show processlist" to see 2 queries left on stack.

1:54pm - Execute "top" command, load is down to 2.7 and falling. 1.9 now.  0.70 now.

1:55pm - Declare crisis averted via instant message and email.  Wonder again if people still use email.

1:56pm - Assign developer responsible for non-indexed table the task of making sure the schema changes get into source code control.

1:57pm - Go back to regular work.

2 comments:

Pete said...

Do you use htop at all? Very cool tool, and it even runs natively right in that black rectangular thingy with the prompt where you have to type text commands you've committed to memory... that you love so much!

Rich said...

htop looks pretty cool, will have to check it out in more depth. I like that you can scroll horizontally to see entire commands, and the nicing of processes is cool too.

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