New feature in iMonitor to troubleshoot eDirectory database locks.

  • 3812871
  • 21-Jun-2007
  • 26-Apr-2012

Environment

Novell eDirectory 8.7.3.9 FTF2 for All Platforms
Novell eDirectory 8.8.1 FTF3 for All Platforms
Novell eDirectory 8.8.2 for All Platforms

Situation

Locks on the eDirectory database are a normal occurance that must happen in order to write data into it. Due to the speed with which it is able to obtain and release a lock and using its builtin design of a single writer but multiple readers users of eDirectory rarely are aware a lock has taken place. However, there are certain circumstances whereby the time required for a thread to obtain a lock can be excessive and affect operations. This could be one of the following: the server is overloaded with modify requests, a current lock is taking to much time and the other write threads are queuing up, misconfiguration, etc. The symptoms of excessive locks can exhibit themselves in high utilization, slowness or unresponsiveness to client requests and long login times.
On NetWare often the Cool Solution NWMON utility was used to identify whether an excessive database lock was the cause by examining its main screen or, more often, allowing the utility to log out these conditions. NWMON could also help in identifying which process was holding the lock for an extended amount of time. However, NWMON is only available for NetWare.

Resolution

There is now a new feature in iMonitor to perform this function. It has been added to eDirectory versions 8.7.3 SP9 FTF2, 8.8 SP1 FTF3 and the coming release of 8.8 SP2. If an excessive database lock is suspected as the culprit for the symptoms mentioned above or if Novell Support asks you to track lock times and submit the logs from this utility then the procedure outlined below will be a guide in setting up the diagnostic logger in iMonitor to track long lock times.
1. Connect to iMonitor via a browser. For instance, on Linux this would be https://x.x.x.x:8030/nds .
2. Once in iMonitor click on the Agent Configuration - Diagnostic Logger links in the left side frame.
3. Once there a page will be displayed similar to the following:
On this page the Diagnostic Logger Configuration settings can be set. In this example logging has been turned on. The threshold has been set to 30 seconds, the logging interval to 120 seconds and the logging interval for warnings is set to 10 seconds. This means iMonitor will consider any lock greater than 30 seconds to be excessive. Until that threshold is reached logging will take place every 120 seconds. When a lock time goes over 30 seconds, logging will take place every 10 seconds until the lock for that particular process is released. Press submit and the logger will start running.
When the symptoms begin happening the log file needs to be viewed in order to see if a excessive lock is occuring. This can be done by clicking on the View Log Data icon. Below is the log view screen:
The output from the log shows an excessive lock has been found according to the parameters set earlier. The data fields do not line up well in iMonitor. The main values of interest at this initial point are the following:
- threshold set for the lock time was reached, indicated by the WARNING status.
- the last column shows the length of time the lock was held
- the description of the thread causing the lock
- the date and time it occured.
The next step is to take the output file from the server and import it into a spreadsheet for easier viewing. The log on the server's local filesystem is called diaglog.csv and can be found in the dib directory. This server is a Linux server running eDirectory 8.7.3 so it can be found in the /var/nds/dib directory.
Much better!
Column A shows the lock began on the 15th of June around 3:36 pm and ended at 3:41 pm. More significantly it ended on its own since column E shows the server was not rebooted and column G shows the daemon was never restarted. (The time display is approximate and does not increment properly in this first version.) Columns J and K show the thread's ID in hex and decimal. These are not terribly useful on Linux since there is no way to crossreference these to the threads found in a core if one is available taken. Of more interest is column L which shows that in this case the Janitor process was holding the lock and held it for 323 seconds as indicated by column M.
This log will be very useful to Novell Support. If using this functionality for a company's own investigation the following questions might be asked:
1. Does the lock time always occur around the same time of day?
2. What is happening in the environment during this time?
3. What has changed in the environment?
4. Grab some dstrace output before the issue occurs to see what activity leads up to the issue.

NOTE:  It is important to be aware that currently after ds is restarted or the server is rebooted that the diagnostic logger settings will revert to off.  An enhancement request has been entered to make this permanent if desired.

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