Merge branch 'pratik/otel-phase10-workload-validation' into pratik/otel-sync-diagnostics

Brings in the phase-10 revert of the nodestore read-latency histogram plus the
nudb_bytes -> stored_object_bytes rename.

Conflicts in MetricsRegistry.{h,cpp} resolved keeping both intents:

- MetricsRegistry.cpp: dropped everything that existed only to serve the
  reverted nodestore_read_us histogram -- the addSubMillisecondHistogramView()
  helper, its call site, the kSubMillisecondBoundaries array and the
  NodeStoreMetricNames.h include. Kept every view this branch registers
  (consensus round duration, sweep_malloc_trim_us, dns_resolve_latency_ms,
  overlay_dial_latency_ms) and the shared addHistogramView() base helper.
  Took the rename at the storage_detail observe() call site.

- MetricsRegistry.h: took phase-10's move of the four nodestore_state observe
  helpers and their ObserveFn sink from private to public, while keeping this
  branch's enriched Doxygen on observeNodeStoreTotals().

Also corrected the registered-view count in the 09 reference doc: neither side's
arithmetic survives the merge, since this branch adds four views phase-10 never
saw and the revert removes one. Ten views are registered now, not six or seven.

include/xrpl/telemetry/NodeStoreMetricNames.h

@@ -1,199 +0,0 @@
-#pragma once
-
-// cspell:ignore ISTOGRAM
-// The all-caps macro name XRPL_METRIC_HISTOGRAM_RECORD trips cspell's
-// compound-word splitter, which emits the subword "ISTOGRAM"; ignore it here.
-
-/**
- * Metric name, description, label key and label values for the per-fetch
- * NodeStore read-latency histogram.
- *
- * The name is referenced from two translation units in two different
- * levelization modules, which is why these constants live in a header rather
- * than in either unit's unnamed namespace:
- *
- *   NodeStoreMetricNames.h
- *          |
- *          +--> NodeStoreScheduler.cpp  (xrpld.app -- the record site, via
- *          |                             XRPL_METRIC_HISTOGRAM_RECORD_LABELED)
- *          |
- *          +--> MetricsRegistry.cpp     (xrpld.telemetry -- registers the
- *                                        explicit sub-millisecond bucket
- *                                        boundaries for the same name)
- *
- * A copy-pasted literal would let the two drift, and a drifted name silently
- * drops the bucket override: the histogram would fall back to the SDK default
- * boundaries, whose lowest edge is far above the single-digit-microsecond
- * range a warm read occupies, so every warm read would land in bucket 0 and
- * the distribution would read as flat. This mirrors the reason
- * GetObjectMetricNames.h exists for the `getobject_*` family.
- *
- * Placed under `include/xrpl/telemetry/` for the same levelization reason as
- * GetObjectMetricNames.h: `xrpld.app > xrpl.telemetry` and
- * `xrpld.telemetry > xrpl.telemetry` are both existing edges (see
- * `.github/scripts/levelization/results/ordering.txt`), so `include/xrpl/` is
- * the one level both consumers can already reach. Both sites include this file
- * as `<xrpl/telemetry/NodeStoreMetricNames.h>`.
- *
- * Example usage -- registering the bucket view (MetricsRegistry.cpp):
- * @code
- * addHistogramView(
- *     *views,
- *     kNodeStoreReadUs,
- *     {kSubMillisecondBoundaries.begin(), kSubMillisecondBoundaries.end()});
- * @endcode
- *
- * Example usage -- edge case: the record site labels one instrument with two
- * independent dimensions, which is why the keys and all four values are
- * constants rather than literals (a misspelling on either side would create a
- * second, silently disjoint series):
- * @code
- * XRPL_METRIC_HISTOGRAM_RECORD_LABELED(
- *     app, kNodeStoreReadUs, kNodeStoreReadUsDesc, elapsed.count(),
- *     {{kFetchTypeLabel, std::string(kFetchTypeAsync)},
- *      {kFetchFoundLabel, std::string(kFetchFoundTrue)}});
- * @endcode
- *
- * @note These are `constexpr char[]`, not `constexpr std::string_view`. The
- * OTel C++ API takes `nostd::string_view`, which on this build is OTel's own
- * type; it converts from `char const*` and from `std::string` but has no
- * converting constructor from `std::string_view`, so a `string_view` constant
- * would not compile at the call sites. Same reasoning as
- * GetObjectMetricNames.h.
- *
- * @note Header-only constants with no runtime state, so there is nothing to
- * synchronize -- safe to include from any thread context.
- */
-
-namespace xrpl::telemetry {
-
-// ===== Metric name and description ==========================================
-
-/**
- * Per-fetch NodeStore backend read latency, in microseconds.
- *
- * Referenced twice: at the record site in NodeStoreScheduler.cpp, and by the
- * sub-millisecond `addHistogramView()` call in MetricsRegistry.cpp. Both must
- * use this one constant.
- */
-inline constexpr char kNodeStoreReadUs[] = "nodestore_read_us";
-
-/**
- * Description for kNodeStoreReadUs.
- */
-inline constexpr char kNodeStoreReadUsDesc[] = "NodeStore backend fetch latency in microseconds";
-
-// ===== Label keys ===========================================================
-
-/**
- * Label key separating an async (read-ahead) fetch from a synchronous one.
- *
- * The two mean different things: a slow async read delays prefetch, while a
- * slow synchronous read blocks a caller outright. Merged into one series they
- * cannot be told apart.
- */
-inline constexpr char kFetchTypeLabel[] = "fetch_type";
-
-/**
- * Label key recording whether the fetch found the object.
- *
- * A miss and a hit have different cost profiles -- a miss can require reading
- * every backend -- so mixing them would blur the distribution that matters.
- */
-inline constexpr char kFetchFoundLabel[] = "found";
-
-// ===== Label values =========================================================
-
-/** @{ */
-/**
- * kFetchTypeLabel values, one per node_store::FetchType enumerator.
- */
-inline constexpr char kFetchTypeAsync[] = "async";
-inline constexpr char kFetchTypeSync[] = "sync";
-/** @} */
-
-/** @{ */
-/**
- * kFetchFoundLabel values. Spelled out rather than emitted as a bool
- * AttributeValue so the exported label text is stable and matches the
- * string-valued convention every other label in this codebase follows.
- */
-inline constexpr char kFetchFoundTrue[] = "true";
-inline constexpr char kFetchFoundFalse[] = "false";
-/** @} */
-
-// ===== Record-site helpers ==================================================
-
-/**
- * Map a fetch's async-ness to its kFetchTypeLabel value.
- *
- * Takes a bool rather than a node_store::FetchType because this header sits in
- * `xrpl.telemetry`, which has no levelization edge to `xrpl.nodestore`. The
- * caller does the one-line enum comparison; this function owns the mapping so
- * the two label spellings live in exactly one place and are unit-testable.
- *
- * @param isAsync True for node_store::FetchType::Async.
- * @return kFetchTypeAsync when @p isAsync, else kFetchTypeSync.
- *
- * @note Pure and reentrant: holds no state and performs no I/O.
- *
- * Example:
- * @code
- * fetchTypeLabelValue(true);   // "async"
- * fetchTypeLabelValue(false);  // "sync"
- * @endcode
- */
-[[nodiscard]] constexpr char const*
-fetchTypeLabelValue(bool isAsync) noexcept
-{
-    return isAsync ? kFetchTypeAsync : kFetchTypeSync;
-}
-
-/**
- * Map a fetch's hit/miss outcome to its kFetchFoundLabel value.
- *
- * @param wasFound node_store::FetchReport::wasFound.
- * @return kFetchFoundTrue when @p wasFound, else kFetchFoundFalse.
- *
- * @note Pure and reentrant: holds no state and performs no I/O.
- *
- * Example:
- * @code
- * fetchFoundLabelValue(true);   // "true"
- * fetchFoundLabelValue(false);  // "false"
- * @endcode
- */
-[[nodiscard]] constexpr char const*
-fetchFoundLabelValue(bool wasFound) noexcept
-{
-    return wasFound ? kFetchFoundTrue : kFetchFoundFalse;
-}
-
-/**
- * Whether an elapsed microsecond count may be handed to the histogram.
- *
- * The OTel SDK rejects a negative histogram value and logs a warning on every
- * such call, so a clock anomaly on a per-fetch path would turn into a log
- * flood. Filtering here drops the bad sample instead.
- *
- * Zero is recordable: a fetch served from a warm page cache can genuinely
- * round to 0 us, and suppressing that would make the fastest reads invisible.
- *
- * @param elapsedUs Measured fetch duration in microseconds.
- * @return True when @p elapsedUs is zero or positive.
- *
- * @note Pure and reentrant: holds no state and performs no I/O.
- *
- * Example:
- * @code
- * shouldRecordFetchLatency(0);   // true  -- genuinely instant read
- * shouldRecordFetchLatency(-1);  // false -- clock anomaly, skip
- * @endcode
- */
-[[nodiscard]] constexpr bool
-shouldRecordFetchLatency(long long elapsedUs) noexcept
-{
-    return elapsedUs >= 0;
-}
-
-}  // namespace xrpl::telemetry