EW-9282 EW-9367 Add STW onset event size limit #4809
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We need to institute some limits on the size of streaming tail worker events, start with the Onset event. Size is counted the same way it is counted for the LTW so far, so some kinds of metadata are not included in it. This also fixes a subtle bug where we would not dispatch the onset for STW at all if it was too big, which caused errors to be logged when trying to dispatch later events.
mar-cf
approved these changes
Aug 19, 2025
| trace->truncated = true; | ||
| eventSize += fetch.cfJson.size(); | ||
| if (trace->bytesUsed + eventSize > MAX_TRACE_BYTES) { | ||
| trace->truncated = truncated = true; |
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Nit: prefer one statement per line
| trace->logs.add(timestamp, LogLevel::WARN, | ||
| kj::str("[\"Trace resource limit exceeded; could not capture event info.\"]")); | ||
| trace->eventInfo = tracing::FetchEventInfo(fetch.method, {}, {}, {}); | ||
| return; | ||
| // Limit STW onset to MAX_TRACE_BYTES, beyond that dispatch a truncated event too. | ||
| if (eventSize > MAX_TRACE_BYTES) { |
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Might be worth to include a short lived, periodic log to figure out if or how often this occurs.
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We need to institute some limits on the size of streaming tail worker events, start with the Onset event. Size is counted the same way it is counted for the LTW so far, so some kinds of metadata are not included in it.
This also fixes a subtle bug where we would not dispatch the onset for STW at all if it was too big, which caused errors to be logged when trying to dispatch later events.