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perf(postgres): reduce per-record allocations in the CDC pull path - #4920
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Two spots in the per-WAL-record path (PullCdcRecords) allocate more than they need to. In a CPU/heap profile of a Postgres source mirror both are a meaningful share of allocations, and the CPU profile is dominated by GC/malloc, so trimming them frees CPU. - processMessage called internal.LoggerFromCtx(ctx) on every message, which goes through temporal log.With and allocates per call. The logger is already built once in PullCdcRecords; pass it in as a parameter. - The unchanged-toast metric was recorded with UnchangedToastValuesCounter.Add plus a fresh attribute.NewSet on every update record. Accumulate the counts in atomics and flush them once a minute with the other CDC counters, reusing two pre-built attribute sets (same pattern already used for FetchedBytesCounter). No behaviour change: same logs, same metric values, fewer allocations.
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Was profiling a Postgres source mirror and noticed CPU is mostly GC/malloc, with a couple of avoidable allocations on the per-record path in PullCdcRecords.
Two small fixes:
processMessage was rebuilding the logger from context on every message. It's already available in PullCdcRecords, so pass it down instead.
The unchanged-toast metric was recording with a freshly built attribute set on every update record. Accumulate the counts and flush them once a minute with the other CDC counters, the same way fetched bytes and friends are already handled.
No behaviour change, just fewer allocations on the hot path.