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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 43728] - Log file loss when specified file is locked
Date Mon, 29 Oct 2007 19:49:13 GMT
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http://issues.apache.org/bugzilla/show_bug.cgi?id=43728





------- Additional Comments From mgeiser@mgeiser.net  2007-10-29 12:49 -------
Using a clustered WebLogic server with two managed server, we misconfigured 
the DailyRollingFileAppender so that both managed servers to use the same log 
file.  

Each managed server runs in it's own JVM and the two JVMS cannot have an 
exclusive lock on the same file (duh!)

I noticed that the log files for previous intervals frequently contained data 
from the wrong time interval, some data was entirely missing and that you have 
to look in the current log as well as the log for the previous interval to 
ensure you get all the logged information.

It appeared one of the JVMs wrote to the previous interval log and over-wrote 
the logs from that interval.

To conclusively demonstrate this was the case, I left both Log4j config files 
specify the same log file but added the sting "MS1" and "MS2" to the 
ConversionPattern parameter for each log file so that it was apparent which 
managed server was writing to which log file.

I saw when both Managed Servers try to log to the same log, one managed server 
writes to the specified file (the Managed Server that does get the lock 
varies) and the other managed server writes to the previous intervalís log 
file.  Since the appenders also do not specify to append to (but instead 
overwrite) files, the previous intervalís log file is overwritten with new 
data.  This also confirmed that a managed server always wrote to the same log 
file instead of each managed server opportunistically writing to any unlocked 
log file. 

We can see demonstrated this below. The first few bytes of the first lines of 
the files are associated with the log file name.    

Prior to 10:00am, only one managed server (MS1) had any activity to log and it 
logged to the docmgt.log file.  
 
At 10:00am, I ran a test were a client ran 10 treads calling an EJB via RMI.  
The 10 calls were balanced by WebLogic across the two managed servers in the 
domain.  When this test ran and both Managed Servers were being used, the log 
data from MS1 that was in the docmgt.log file was now located in 
docmgt.log.2007-10-28-PM (the docmgt.log file at 9:58 was renamed) and the 
data from MS2 was logged to the docmgt.log file.  The data that was in 
docmgt.log.2007-10-28-PM prior to 10:00am was over-written and lost. 

at 9:58 am 
docmgt.log                |MS1|20071029||08:56:05,850||
docmgt.log.2007-10-28-PM  |MS2|20071028||21:20:08,318||
docmgt.log.2007-10-27-PM  |MS1|20071028||21:19:41,689||
docmgt.log.2007-10-27-AM  |MS2|20071027||19:55:26,386||
docmgt.log.2007-10-26-PM  |MS1|20071026||12:59:47,760||  
docmgt.log.2007-10-26-AM  |MS1|20071027||00:46:54,637||
docmgt.log.2007-10-25-PM  |MS2|20071026||09:15:08,077||

at 10:01
docmgt.log                |MS2|20071029||10:00:22,993||                
docmgt.log.2007-10-28-PM  |MS1|20071029||08:56:05,850||
docmgt.log.2007-10-27-PM  |MS1|20071028||21:19:41,689||
docmgt.log.2007-10-27-AM  |MS2|20071027||19:55:26,386||
docmgt.log.2007-10-26-PM  |MS1|20071026||12:59:47,760||  
docmgt.log.2007-10-26-AM  |MS1|20071027||00:46:54,637||
docmgt.log.2007-10-25-PM  |MS2|20071026||09:15:08,077||

Although we could specify the append parameter be true, overwritting the file 
in this case is clearly a bug.  It is important to perform the log, but there 
is not alert that there is a file contention and it would be infinately 
preferable that the previous interval log NOT be overwritten.  add a short 
random sting or time stamp to the log file name specified in the appender if 
nothing else.







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