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No, it is not possible. You could consider defining a database event that will truncate the transaction log when it reaches a certain size. The sample below, taken from the documentation, limits the size of the transaction log to 10 MB. CREATE EVENT LogLimit TYPE GrowLog WHERE event_condition( 'LogSize' ) > 10 HANDLER BEGIN IF EVENT_PARAMETER( 'NumActive' ) = 1 THEN BACKUP DATABASE DIRECTORY 'c:\\logs' TRANSACTION LOG ONLY TRANSACTION LOG RENAME MATCH; END IF; END; 1
The real advantage over using "dbeng -m" would be that this will create a backup of the log, so you are able to recover in case of a media failure (if the backup is not damaged, as well, obviously) - whereas with -m, you risk data loss.
(12 Sep '12, 16:13)
Volker Barth
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Thank you, that will do it.
(14 Sep '12, 02:23)
henginy
FWIW, if you do not need a backup at all and just want to truncate the log, use BACKUP DATABASE DIRECTORY '' TRANSACTION LOG ONLY TRANSACTION LOG TRUNCATE; in the above sample. (Cf. my comment under Breck's anwer...)
(15 Sep '12, 07:39)
Volker Barth
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Sometimes recovery takes a back seat to administration and performance issues; e.g., when an embedded database is recreated on demand and used for transient data. You might consider using a DatabaseStart event to confirm that the database was started with -m, and if not, take some action. AFAIK there is no easy way to determine whether or not -m is in effect, but this code seems to work in Version 12: SELECT IF PROPERTY ( 'CommandLine' ) LIKE '%-m%'
THEN 'Y'
ELSE 'N'
END IF AS truncate_log_on_checkpoint;
truncate_log_on_checkpoint
'Y'
...though it could mean any database was started with -m, not necessarily the current one, right? (Yep, autostarting several embedded databases is rather uncommon, and I'm just splitting hairs:))
(12 Sep '12, 17:12)
Volker Barth
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One other small caveat to such an approach would be that there are other (undocumented) server switches that also start with "-m", that you may be asked by Technical Support to start the server with for diagnostic purposes. You may want to consider scanning for the switch
(13 Sep '12, 17:14)
Jeff Albion
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Thank you all for the insight.
(14 Sep '12, 02:27)
henginy
Since -m is a server option, not a database option, I assume -m applies to all databases named on the command line. However, I don't know what happens to a subsequent START DATABASE command that doesn't have the WITH TRUNCATE AT CHECKPOINT clause... does the command line -m apply to that database as well? I would put money on "yes" since that would obey the rule "Watcom does things the way they should be done.
(14 Sep '12, 09:00)
Breck Carter
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Yes indeed... plus, if one thought it possible to code -m at the end of a command line, the predicate should be extended to cover that case: IF PROPERTY ( 'CommandLine' ) LIKE '%-m %' OR PROPERTY ( 'CommandLine' ) LIKE '%-m'
(14 Sep '12, 09:02)
Breck Carter
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Many bugs are the result of unsplit hairs... splitting hairs is a job requirement :)
(14 Sep '12, 09:04)
Breck Carter
FWIW, like "-n", "-m" does exist both as database server and as database option, so its meaning is influenced by its position on the command line...
(14 Sep '12, 09:23)
Volker Barth
I live and learn... perhaps a more reliable (albeit brutish) solution would be to compare the transaction log file size before and after doing an explicit CHECKPOINT :)
(14 Sep '12, 15:25)
Breck Carter
I guess the reliable solution is to get rid of "-m" and use a method to backup and truncate the transaction log, as Reg has suggested - at least Henginy seems to be content with that:) Af if you really don't need to be able to recover, the following backup statement variant would just omit the backup, just truncate: BACKUP DATABASE DIRECTORY '' TRANSACTION LOG ONLY TRANSACTION LOG TRUNCATE; Apparently, that could be used in Reg's event sample, too.
(15 Sep '12, 07:37)
Volker Barth
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