Thomas,
On 1/26/23 03:00, Thomas Meyer wrote:
Am 18. Januar 2023 23:20:29 MEZ schrieb Christopher Schultz
<ch...@christopherschultz.net>:
Thomas,
On 1/17/23 13:33, Thomas Meyer wrote:
Does Tomcat's CP support exponential backoff in case DB is unavailable for some
reason?
I didn't find anything in the documentation in this regards.
I don't think is supports any such thing. What would be the purpose of
exponential back-off... don't you want to connect ASAP?
Hi,
Not really sure, but I think the idea is to protect the database from getting
overloaded with requests once it's coming up again.
Sadly the description given in
https://cloud.google.com/sql/docs/postgres/manage-connections#backoff
Is very vague and I think won't really help much to mitigate above problem, if
any.
I found this interesting article and test class that tries to demonstrate the
resp. behavior of the situation:
https://github.com/brettwooldridge/HikariCP/wiki/Bad-Behavior:-Handling-Database-Down
https://github.com/brettwooldridge/HikariCP-benchmark/blob/master/src/test/java/com/zaxxer/hikari/benchmark/DbDownTest.java
There seems also to be an reply to above benchmark from the vibur dbcp author,
which has some interesting points:
https://github.com/brettwooldridge/HikariCP/issues/230
While investigating the reason of why exponential backoff would make sense I
also did stumble across this article:
https://aws.amazon.com/de/blogs/architecture/exponential-backoff-and-jitter/
This article make much more sense in my head, I.e. use exponential backoff with jitter to
protect the restarting database from getting "flooded".
But HikariCP does only support plain exponential backoff and probably won't
help much in above described situation, because once the database is starting
to accept connections again, all HikariCP connections will probably align at
the same time to start creating connections again.
If you are worried abou tyour database being flooded with requests, you
should limit the number of connections your database will accept /at the
database/.
If you have 10 applications connecting to the db each with their own
connection pools, even exponential backoff won't help avoid all of them
(separately!) flooding the database.
-chris
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