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Alex BandClaude Opus 5.5
8d2ae405e8
Refs #2148. ## Problem `StoreObs` is the store's most numerous struct: 400k of them on a week of a busy regional network. Its lazy timestamp cache (#1481) is a `time.Time`, a `sync.Once` and a `bool`, together 40 bytes. On current master that makes the struct 200 bytes, which puts every observation in the 208-byte size class. ## Change The cache is now a single `atomic.Int64`: - `0` before the first call; - the parsed time as UTC nanoseconds after it; - or one of two sentinels: one for empty or unparseable strings, and one for times it can't hold exactly (a non-UTC offset, or outside `UnixNano`'s range). Those are re-parsed on each call so their location is preserved. Concurrent first calls may both parse; they store the same value. `StoreObs` is now 160 bytes, in the 160-byte size class: 48 bytes × 400k observations ≈ **19 MB** less heap. The first parse costs the same; cached reads now build the `time.Time` from an int. ## Tests - `TestStoreObsFitsIn160Bytes`: red commit first. - `TestStoreObsParsedTimeMatchesParse`: Z, nanosecond, offset, SQL, empty, garbage and epoch inputs give the same time and location as `time.Parse`, on the first and the cached call. - `TestStoreObsParsedTimeConcurrentFill`. - The existing `storeobs_parsedtime_test.go` still passes. - `go test ./cmd/server` passes, and `-race` passes on the ParsedTime, retransmission and observer analytics tests. ## This PR or #2149 #2149 fixes #2148 by reordering these same three fields. The two conflict, so here is how they compare. Sizes are `unsafe.Sizeof(StoreObs{})` on each branch, with Go's heap size class beside them: | | struct | heap per observation | saved per observation | saved at 400k observations | |---|---|---|---|---| | master | 200 B | 208 B | – | – | | #2149 (field reorder) | 192 B | 192 B | 16 B | ~6.4 MB | | this PR (one 8-byte field) | 160 B | 160 B | 48 B | ~19 MB | - **#2149:** a pure field reorder with no change in behaviour. It is the smallest, safest change and the easiest to review. It saves a third of what this PR does. - **This PR:** three times the saving, but more code. It adds two sentinel values, and re-parses on each call any timestamp with a non-UTC offset. The store writes UTC (`Z`), so that path is rare. It is tested against `time.Parse` on edge cases, concurrently, and under `-race`. Options: 1. **Take this PR.** #2149 then has nothing left to reorder. 2. **Take #2149 now, and this PR after it** as a follow-up for the further 32 bytes per observation. I'll rebase onto #2149 if it lands first. 3. **Take only #2149** if the smaller, simpler change is preferred. No config or UI changes. 🤖 Generated with [Claude Code](https://claude.com/claude-code) https://claude.ai/code/session_01KaR4xu8gVykQBkH8yG8m6H --------- Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>