Batch calling of `updateIssuesMeta` causes database deadlock

[wxiaoguang]

Gitea Version

dev(main)

Description

Bug:

gitea/web_src/js/features/repo-legacy.js

Lines 87 to 91 in 141d1a2

	const promises = [];
	Object.keys(items).forEach((elementId) => {
	const item = items[elementId];
	const promise = updateIssuesMeta(
	item['update-url'],

It causes database deadlock and results in error response (some data can not be updated correctly, and the page can not be reloaded)

2021/10/28 17:51:22 .../repo/issue_label.go:209:UpdateIssueLabel() [E] RemoveLabel: Error 1213: Deadlock found when trying to get lock; try restarting transaction
2021/10/28 17:51:23 Completed POST /root/test/issues/labels 500 Internal Server Error in 421.528354ms

[wxiaoguang]

Blocked by

• Improve async/await usage, and sort init calls in index.js #17386

I do not want to make huge conflicts between PRs.

[lunny]

It seems it's also a backend bug.

[wxiaoguang]

The bug is mostly related to frontend, the concurrency API calls are incorrect.

For backend, not that related, the only thing it can do is wrapping the deadlock error and returning a friendly error response. The deadlocks can not be fully avoided in normal cases.

[zeripath]

The db should never deadlock - this is a backend bug.

[wxiaoguang]

The db should never deadlock - this is a backend bug.

If two users update the same records at the same time with transactions, the database may report a dead lock. It is a correct database behavior.

Database deadlock is not the same as code deadlock. If you need more information, I can explain more.

For this problem (deadlock in UpdateIssueLabel), it's difficult to make a lock-safe transaction, because the logic is pretty complicated, many inserts and updates. However, if we can make the frontend send the updated labels in one request, then there will be no dead lock problem for most cases, except two users are updating the same issue at the same time (in such case, reporting an error to end user is also a good choice to prevent they overwrite other's labels).

[lunny]

Is this resolved?

[wxiaoguang]

Not yet, I haven't got time for this. (If someone can help that's also very welcome)

[wxiaoguang]

I proposed a simple fix, please review.