Suvendu,
On 11/11/20 06:40, Suvendu Sekhar Mondal wrote:
Application Setup:
AdoptOpenJDK 1.8.192, Tomcat 7.0.55, Apache httpd, Windows 2012, SQL Server 2016
As Michael pointed-out, these all need to be upgraded, but they are not
affecting your experience, here.
Observations:
After database failover, we noticed that HTTP thread pool size jumped
from 10 to 50. No. of busy threads jumped to 40 for a minute and then
came down to normal range(1-5). But thread pool size remained 50 for
the next one hour. When we collected the heap dump after one hour,
thread pool size jumped again to ~90. Thread dump analysis is showing
most of the HTTP threads were just waiting to get some work[1]. That
looked surprising to me. Few of them are runnable and doing some work
- which matches "busy thread" count. During all this timeframe load on
the system remained the same.
We have 30sec connectionTimeout. Also TTL is set to 300 in httpd. We
do not have any keepAliveTimeout set in Tomcat. App uses session
affinity. We were looking for some connector properties which deal
with idle threads but found none[3].
You won't find them.
We are not seeing any "problem" in our app after DB failover but this
is something also newer to us and we are trying to explain it.
What are you trying to explain?
Tomcat's memory usage increased by a few MB as new threads were
spawned. My expectation was that if threads in the thread pool are not
getting used and idle, after sometime thread pool size will reduce to
"minSpareThreads" size which is 10 in our case. Is that expectation
wrong? Can you please share your thoughts?
This is a common misconception. If you do not configure an "executor"
then Tomcat will create one for you and it will NOT remove idle threads
from the thread pool.
The solution is to manually-specify an Executor:
<Executor name="myExecutor" namePrefix="myExecutor-" maxThreads="X"
minSpareThreads="Y" />
<Connector executor="myExecutor" ... />
With this configuration, you should see your thread count stay between Y
and X, but when X are not necessary, your thread count should drop
towards Y as appropriate.
Hope that helps,
-chris
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