Is it appropriate to return HTTP 503 in response to a database deadlock?

Question

Is it appropriate for a server to return 503 ("Service Unavailable") when the requested operation resulted in a database deadlock?

Here is my reasoning:

Initially I tried avoiding database deadlocks, but I ran across https://stackoverflow.com/a/112256/14731
Next, I tried repeating the request on the server-side, but I ran across Java Servlets: How to repeat an HTTP request?. Technically speaking I can buffer the request entity but scalability will suffer and clients are more likely to see 503 Service Unavailable anyway.

Seeing as:

It's easier to ask clients to repeat the operation.
They need to be able to handle 503 Service Unavailable anyway.
Database deadlocks are rather rare.

I'm leaning towards this solution. What do you think?

UPDATE: I think returning 503 ("Service Unavailable") is still acceptable if you wish it, but I no longer think it is technically required. See https://stackoverflow.com/a/17960047/14731.

Even if you program this in production you may still end up with timeout, which would cause your load balancing proxy to send 504 to client. — Victor Olex, May 20 '13 at 07:58
@agilevic, what do you mean? Are you saying I need to ensure deadlock-by-timeout is configured to use a small timeout value to avoid `HTTP 504`? — Gili, May 20 '13 at 16:51
Database deadlocks can last longer than load balancer's timeout thus blocking the response. If you are capable of detecting a deadlock before that timeout you can respond to client with 503 - a sensible choice. — Victor Olex, Oct 22 '13 at 04:09

score 2 · Answer 1 · answered Jul 06 '17 at 10:42

I think semantically 409 Conflict is a better alternative - basically if you have a deadlock there's contention for some resource, and so the operation could not be completed.

Now depending on the reason for the deadlock, the request may not succeed if submitted a second time, but that's true for anything.

For a 503, as a client I'd implement some sort of back-away/circuit breaker operation as the system is rate limited, whereas 409 relates to the specific request.

score 1 · Answer 2 · answered Feb 18 '21 at 15:30

Just got here with the same question and no clear answer on the issue.

a 503 is acceptable but might not be correctly interpreted
a 409 is also OK but in my case was not OK (since multiple resources could end up returning a this error for the same URL)

In my case I ended up returning a 307 redirect on the same URL.

Clients will automatically "retry" and the second call works because the resource is only raising a deadlock during its initial creation.

Be warned that might end up in an infinite loop

score 0 · Accepted Answer · answered May 18 '13 at 21:00

0

I think it's fine so long as the entire transaction is rolled back or if the request is idempotent.

answered May 18 '13 at 21:00

Miguel

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Is it appropriate to return HTTP 503 in response to a database deadlock?

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