BUG: Waiting on wrong key #24
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| return value if value.present? | ||
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| # wait for the other process if a last known value isn't there | ||
| if key.present? | ||
| return time('wait.run', tags: tags) do | ||
| wait_for_new_value(key, options, tags) | ||
| wait_for_new_value(keyspace, options, tags) |
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quick_retry and wait_for_new_value changed their approach here a bit:
quick_retrynow uses the initial key obtained on line 40, as very little time has passed, and it's more efficient for all the locations that have quick_retry disabled.wait_for_new_valueno longer takes the key, as time will have elapsed between attempts, such that it should make sure it's looking at the most recent key for a value.
| @@ -162,6 +159,8 @@ def wait_for_new_value(key, options, tags) | |||
| backoff_duration_ms = option(:backoff_duration_ms, options, backoff_duration_ms) | |||
| sleep((backoff_duration_ms.to_f / 1000) * attempt) | |||
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| # re-fetch the key each time, to make sure we're actually getting the latest key with the correct LMT | |||
| key = @timestamp_manager.current_key(keyspace) | |||
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This line here is effectively the bug fix. Each attempt it will make sure to get the most current key.
How this is actually working in a cold start scenario is that because LMT is empty, the initial key is just prefix.foobar. The value that actually gets written by the generating process however is prefix.foobar.timestamp. The old code would continue to try and read prefix.foobar then exhaust it's attempts. This fix causes it to always grab the most current key, which will cause it to see prefix.foobar.timestamp as written by another generating process, and use that key for a value.
| end | ||
| end | ||
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be warned: there be dragons below 🐉
🙈
Background
A bug was identified earlier today where the
wait_for_new_valuemethod is incorrectly waiting on the wrong key. This bugfix updates the code to re-fetch the latest key value whenever it attempts to see if another thread has written the value. This makes sure that re-attempts are always attempting to get the latest value.Tasks
./lib/atomic_cache/version.rb) when applicable