[Building Sakai] Gradebook related production incident

[Zhen Qian]

Hi, all:

We had a production issue with Gradebook usage recently, and filed
SAK-26153<https://jira.sakaiproject.org/browse/SAK-26153>for it.

In summary, we had a large course site (1800 users) with many categorized
Gradebook entries (70 GB items). Instructor sent out "grade available"
announcement, and students all log in around the same time to check the
final course grade.

Upon every student login, the base GB query gets all students grade records
for all GB items in site (count=100K). The problem is that there is NO
caching implemented, so this query quickly ate up all available db
connection pool and brought down app servers.

We are running a customized branch based on Gradebook 2.9.2.

Has anyone seem similar problems in production? I looked at the latest
trunk code for Gradebook, and did not find any recent caching fixes, either.

Thanks,

- Zhen
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