Eric,
On 5/31/24 13:44, Eric Robinson wrote:
-----Original Message-----
From: Christopher Schultz <ch...@christopherschultz.net>
Sent: Friday, May 31, 2024 12:38 PM
To: users@tomcat.apache.org
Subject: Re: Database Connection Requests Initiated but Not Sent on the Wire
(Some, Not All)
Mark,
On 5/31/24 12:44, Mark Thomas wrote:
On 31/05/2024 16:09, Eric Robinson wrote:
The results are looking great so far.
Excellent.
Here's what we know:
Before the patch, we had 2 load-balanced tomcats in production for
this customer. Due to the driver search bottleneck, we were seeing
hundreds of stuck threads during the slowdown periods. To work around
this problem, we threw more tomcats at it. With 6 tomcats, the load
was spread around enough to keep the bottleneck condition from
manifesting badly, and users did not complain as much. We were still
seeing dozens of stuck threads, but not hundreds.
After the patch, we went back to 2 tomcats.
I appreciate the show of faith! I think that is braver than I would
have been but it does rather confirm both the problem and the fix.
During the same timeframe today, there have been 1 stuck thread on
Tomcat A and 6 on Tomcat B.
That is great news.
If the numbers hold, this works out to roughly a 10,000% improvement.
Not bad for free support ;)
Seriously, I am glad that we seem to have tracked down the root cause
and that you have a temporary fix that works until such time (probably
the July releases) that we can figure out how we want to address
caching of "not found" classes.
Yeah... this doesn't seem like a great default policy for a few reasons:
1. Maybe the classes will appear in the future? JSPs? Plugins that
speculatively-
load, then fail, then download/update, then try again? I'm grasping at straws a
little, here.
2. Huge numbers of cache misses will cause huge numbers of cached "not
found" entries. Potential DOS? I guess that would be an application bug if it's
allowing huge numbers of random class-loading requests. Again, grasping at
straws.
Would it, though? I don't know what a negative cache entry would look like, but
it seems to me that it would not have to create duplicates.
I was thinking of cache entries for large numbers of different classes,
all of which were "not found". Not one class being requested over and
over again. It's just lots of String keys in a hash map or whatever. Not
horrific, but can get out of control of Something Goes Wrong.
-chris
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