shards: only trigger rescan on .zoekt files changing#801
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Any write to the index dir triggered a scan. This means on busy instances we are constantly rescanning, leading to an over-representation in CPU profiles around watch. The events are normally writes to our temporary files. By only considering events for .zoekt files (which is what scan reads) we can avoid the constant scan calls. Just in case we also introduce a re-scan every minute in case we miss an event. There is error handling around this, but I thought it is just more reliable to call scan every once in a while. Note: this doesn't represent significant CPU use, but it does muddy the CPU profiler output. So this makes it easier to understand trends in our continuous cpu profiling. Test Plan: CI
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stefanhengl
approved these changes
Aug 2, 2024
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That seems fairly frequent for a fail-safe? Isn't this roughly in the order of magnitude we scanned before this PR? I might be totally off though ;-)
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We are always scanning right now on dotcom. IE as soon as one scan is done another starts. The scanning doesn't take long (~50ms?) but effectively we do this for { scan() }. So once a minute seems good?
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Any write to the index dir triggered a scan. This means on busy instances we are constantly rescanning, leading to an over-representation in CPU profiles around watch. The events are normally writes to our temporary files. By only considering events for .zoekt files (which is what scan reads) we can avoid the constant scan calls.
Just in case we also introduce a re-scan every minute in case we miss an event. There is error handling around this, but I thought it is just more reliable to call scan every once in a while.
Note: this doesn't represent significant CPU use, but it does muddy the CPU profiler output. So this makes it easier to understand trends in our continuous cpu profiling.
Test Plan: CI