Garbage collection & TSL warnings...why now?
I was recently pinged by a friend who is rolling out LH in their production environment. They were having an interesting issue where the LH DC showed these two events, in this order:
(event log entries snipped some for brevity)
Log Name: Directory Service
Source: NTDS General
Event ID: 1859
Task Category: Garbage Collection
Level: Warning
User: ANONYMOUS LOGON
Description:
Internal event: The current garbage collection interval is larger than the maximum value.
Current garbage collection interval (hours):
40000
Maximum value:
168
New value:
168
Log Name: Directory Service
Source: NTDS General
Event ID: 1088
Task Category: Internal Configuration
Level: Warning
User: ANONYMOUS LOGON
Description:
Internal event: The following tombstone lifetime registry value is too low or incompatible with the following garbage collection interval specified in the Active Directory Domain Services Configuration object. As a result, the following default registry values for the tombstone lifetime and garbage collection will be used.
This is an old domain which has been around for years. The win2k3 boxes are chugging along without a problem…only the LH boxes were throwing this event. So, the question is, what’s going on?
I took a peak at this for this friend and came up with the following. Thought I’d share it in case others see this too.
First event, the GC one. Well, the event told you the problem. J The GC interval is set to 40000 hours. That’s roughly “a long time.” GC interval is huge, we didn’t like it. We enforce in the product that GC is no greater than a week, in hours. So we went ahead and, in memory, set this to a week.
NOTE: We do not change the setting in the DS, we simply ignore it and use our own. So the setting stays wrong in AD.
Next event, the TSL event. This is the more interesting event. Well, we check a few things here. First, we make your TSL is greater than the min….check, this customer had a value which was ok (I forget, but it was somewhere in the teens). Next we check if the TSL is greater than 3 times the GC interval. You failed. Your GC interval is now 7 days (remember before I said it would set it to a week as your GC interval was nonsensically huge) but your TSL is not 3 times that. So we freak and show you the event. We further set TSL to the default in code, which is 60 days. Again, no config change, just in memory change.
Last item…why now? What changed? Why did this customer not get this before on 2k3? No values changed, after all.
This code is largely identical except for a small change. In 2k3 the code for this event firing code throws the event if GC logging is set to 2 or above. In LH, it fires the event if logging is set to 0 or above. Since all of the customer’s machines were set to 0, this explains why 2k3 didn’t throw an event whereas LH did.
(Personally, I’m happy about this change…I think we should have always flagged this condition. It’s weird, we should have always drawn your attention to it.)