delete from table without locking it

looking for the most efficient method to delete multiple records from tables
without locking them for other users

when i try    Begin Transaction
                        Delete from [table name]
                        Where ....

sometimes table(s) gets locked, looking for more elegant / intuitive way to get that done

Thanks in advance,
-Alex



AlexF777Asked:
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Aneesh RetnakaranDatabase AdministratorCommented:
it's because of lock escalation, when there are more than 5000 rows has to be deleted the lock will be esacalated to a page level or a table level lock, the ebest option will be to delete records below that number

SET ROWCOUNT 4000
Here:
  DELETE FROM [table name]
  Where ....
  IF ROWCOUNT = 4000
  GOTO Here;



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Éric MoreauSenior .Net ConsultantCommented:
do not use transaction when you don't want to lock to much. Also, you can always redo a Delete operation with the same where clause so transactions are not as important as for other operations.

ensure that there is an index on the fields covered by your where clause to be as effective as possible.
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skullnobrainsCommented:
you cannot prevent mysql from locking either the table or the rows depending in the engine you use.

assuming you are using innodb, you can do two things
1) delete using a limit clause and run the delete as many times as needed. looks dumb but experience proves it is a workable solution in many environments
2) use different transaction_isolation_level (s). beware this helps in many cases but will also make your database less ACID compliant which you may or may not want
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skullnobrainsCommented:
you can also use handlers instead of selects for some statements,

and you can also avoid deadlocks by changing some queries so deletes and selects lock in the same order, and possibly lock gaps as well

you definitely need to think that if mysql moves to page or table locking, it is right to do so because it will actually be more efficient or it detected an existing or potential deadlock

----

if what you delete is chunks of data overtime, partitionning horizontally by date and removing partitions instead of rows may be a good idea (the operation will be instantaneaous)

----

give us more information about what happens when you get the locks, maybe the output of "show full processlist" would help us to understand better
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Anthony PerkinsCommented:
>>Zones:SQL Server 2008, SQL Server 2005, MySQL Server<<
You may want clarify what database you are using, as there appears to be some confusion on that subject.  Is it MS SQL Server or MySql?
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skullnobrainsCommented:
yep. fyi handlers are not available on sql server, but cursors indirectly produce a similar functionnality.
for the rest, what was said above concerning innodb should also be true using mssql

deleting with a LIMIT clause should be portable on mssql by doing something like
DELETE TOP (100) FROM ...
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