Hello This subject is not easy to explain in plain words it would be much easier for you with a picture - perhaps you can find one in the documentation - but nevertheless I will try it.
In the releases before 7.4 SAP DB writes the before images (undo entries) into the archive log and the archive log is written circadian. Only this log can be overridden which is older then the last savepoint and the first_not_saved position. If the distance from the current log write position reaches the _LOG_START_COPY distance related to the end of the log a server task is started. This servertask copies the oldest logentries of all currently open transactions into log files (page chains). When all logentries of open transactions in the area between the oldest logpage and _LOG_COPY_DISTANCE are copied into log files the archive log can be overridden. Each transaction has their own log file with copied logentries. If a transaction has logentries which were copied from the archive log to a log file and it must rollback then the logentries are read from the archive log until the copy position is reached and then the log entries are read from the log file. Log files are located in the data volumes like the primary table files (b-trees). If a transaction produces a huge amount of log entries in worst case it causes a database full situation because the log file which contains the outcopied logentries grows and grows and consumpts the whole data volume. The enabled autosave log process and the automatically triggered savepoints do not prevent the need for copying log entries. I hope this will answer your question. Bye, Uwe > -----Original Message----- > From: Mark Thomas [mailto:[EMAIL PROTECTED]] > Sent: Montag, 29. April 2002 17:23 > To: SAPDB general > Subject: Long Transactions > > > Hello, > > I used to run into long transactions when using Informix, and I was > wondering how SAP DB would handle a similar situation. > Informix 7.3 would > force a rollback if an open transaction consumed half of the > available log > (so that it would have enough log space to complete a > rollback, if I recall > correctly). > > I am wondering what SAP DB would do if a single transaction > tried to consume > more than half the available log space. Would it force a > rollback? Would > the behavior differ if Autolog were enabled? > > Thanks. > > -- > Mark "T.C." Thomas > United Drugs _______________________________________________ sapdb.general mailing list [EMAIL PROTECTED] http://listserv.sap.com/mailman/listinfo/sapdb.general
