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From:Dan Nelson Date:December 22 2006 3:50pm
Subject:Re: Befuddled Why This Locks
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In the last episode (Dec 21), Jason J. W. Williams said:
> If someone could suggest some advice/guidance I would be very
> grateful. I'm trying to determine why the following SELECT query
> table locks the "bad_behavior" table referenced the query.
> 
> 'bad_behavior' is MyISAM
> 'c' is InnoDB
> 'a' is InnoDB
> 
> Query:
> select item_p from (select inet_ntoa(ip) as
> item_p,sum(if(class_factor>0.75,1,0)) as info,count(*) as count from c
> join a on c.mid=a.mid where c.date > subdate(now(),interval 6 hour) &&
> ip not in (select address from bad_behavior where score >= 6 ) group
> by ip) as t1 where info >= 5 && info/count >= 0.75
> 
> The befuddling part is that the bad_behavior table is table locked
> (preventing updates/inserts) until the query above ends. The version
> of MySQL is 5.0.27.

I don't see anything wrong here.  "bad_behavior" is a MyISAM table
which uses table locks, so when your select is running, it grabs a read
lock on the table and blocks other writers.  See the chapters at
http://dev.mysql.com/doc/refman/5.0/en/locking-issues.html for more
detail and some tips on how to insert data even on read-locked tables.

-- 
	Dan Nelson
	dnelson@stripped
Thread
Befuddled Why This LocksJason J. W. Williams22 Dec
  • Re: Befuddled Why This LocksDan Nelson22 Dec
    • Re: Befuddled Why This LocksJason J. W. Williams22 Dec
      • Re: Befuddled Why This LocksDan Nelson22 Dec