Incidents/2022-05-20 Database slow

document status: final

Summary

Incident metadata (see Incident Scorecard)

Incident ID	2022-05-20 Database slow	Start	2022-05-20 09:35:00
Task	T308380	End	2022-05-20 09:35:00
People paged	26	Responder count	10
Coordinators	jwodstrcil	Affected metrics/SLOs
Impact	Two occurrences of impact on uncached traffic (high latency, unavailability) related to application server worker thread exhaustion caused by slow database response.

On 2022-05-14 at 8:18 UTC there was a 3 minute impact on uncached traffic (high latency, unavailability) related to application server worker thread exhaustion caused by slow database response. There was no clear root cause at the time. The incident occurred again on the same database host on 2022-05-20 at 09:35 UTC, this time lasting for 5 minutes. After further investigation the likely root cause is a MariaDB 10.6 performance regression under load, further researched in https://phabricator.wikimedia.org/T311106.

Documentation:

• MediaWiki Exceptions

Actionables

• Investigate mariadb 10.6 performance regression during spikes/high load

Scorecard

Incident Engagement™ ScoreCard

	Question	Answer (yes/no)	Notes
People	Were the people responding to this incident sufficiently different than the previous five incidents?	no
	Were the people who responded prepared enough to respond effectively	yes
	Were fewer than five people paged?	no
	Were pages routed to the correct sub-team(s)?	no
	Were pages routed to online (business hours) engineers? Answer “no” if engineers were paged after business hours.	yes
Process	Was the incident status section actively updated during the incident?	no
	Was the public status page updated?	yes
	Is there a phabricator task for the incident?	yes
	Are the documented action items assigned?	yes
	Is this incident sufficiently different from earlier incidents so as not to be a repeat occurrence?	yes
Tooling	To the best of your knowledge was the open task queue free of any tasks that would have prevented this incident? Answer “no” if there are open tasks that would prevent this incident or make mitigation easier if implemented.	yes
	Were the people responding able to communicate effectively during the incident with the existing tooling?	yes
	Did existing monitoring notify the initial responders?	yes
	Were the engineering tools that were to be used during the incident, available and in service?	yes
	Were the steps taken to mitigate guided by an existing runbook?	yes
Total score (count of all “yes” answers above)		11