This article was previously published under Q62866
Listed below are some reasons why the transaction log fills up and never gets truncated, even though the "trunc. log on chkpnt" option is set to true and regular checkpoints are done during processing.
An unbounded update fills up the log; that is, there is no WHERE clause onthe UPDATE statement. Since a transaction (either user declared orimplicit) must be able to be entirely rolled back or committed as a whole,the log must be large enough to maintain all information for thetransaction. Thus, even when truncating the log, it is possible to fill thelog if it is too small for a single large transaction.
This situation can also occur if a WHERE clause is used, the table is verylarge, and the WHERE clause is too general, causing a large number ofrecords to be affected. There is another case where this could happen: ifmultiple updates are performed that together affect enough records to fillthe log before the checkpoint is done, the log can still fill up.