diff --git a/CLAUDE.md b/CLAUDE.md
index 75610494..69af6317 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -934,10 +934,11 @@ only the recorder + outbox knobs:
|---|---|---|
| `Enabled` | `false` | `true` (with `ServerHistorian` configured) wires + spawns the recorder |
| `OutboxPath` | `""` (required when enabled) | **Directory** holding the FasterLog segment + commit files. In production set an **absolute** path on durable storage |
-| `CommitMode` | `PerEntry` | `PerEntry` = fsync before each append returns (no loss window); `Periodic` = batched commits every `CommitIntervalMs` |
+| `CommitMode` | `PerEntry` | `PerEntry` = fsync before the append returns (no loss window); `Periodic` = batched commits every `CommitIntervalMs`. ⚠️ `PerEntry` now means **one fsync per ingest burst, not per value** — the recorder appends a burst through `AppendBatchAsync`, which enqueues every entry then issues a single group commit; the call still does not return until that commit lands |
| `CommitIntervalMs` | `100` | Periodic-mode commit cadence; required `> 0` only under `Periodic` |
-| `DrainBatchSize` | `64` | Entries peeked + written per drain pass |
+| `DrainBatchSize` | `1024` | Entries peeked + written per drain pass. **Raised from 64**: the peek is an in-memory scan and the pass is bounded-parallel (not sequential), so a wide batch no longer costs `tags × latency` — while 64 drew down ≤ 64 entries per `DrainIntervalSeconds`, letting the outbox fall permanently behind during any gateway hiccup |
| `DrainIntervalSeconds` | `2` | Steady drain cadence (and post-success reschedule) |
+| `DrainConcurrency` | `8` | Historian tags one drain pass writes **concurrently** (a batch is grouped per tag; each group is its own gateway round-trip), so a sequential `tags × latency` pass becomes `⌈tags / concurrency⌉ × latency` with outstanding round-trips bounded. `1` = fully sequential. The ack is unchanged — all-or-nothing after every group reports, and the #538 quarantine still keys on "another group wrote this pass" |
| `Capacity` | `500000` | Max un-acked outbox entries before drop-oldest; `0` = unbounded. Non-zero **by default since #538** — the disk backstop for a historian refusing *every* write, the one case the per-tag quarantine deliberately cannot resolve |
| `MaxWriteAttempts` | `5` | #538: consecutive failed drain passes one tag may accumulate — counted **only across passes where other tags wrote successfully** — before its queued entries are abandoned so the FIFO head can advance |
| `MinBackoffSeconds` | `1` | Initial retry backoff after a failed drain pass |
diff --git a/docs/Configuration.md b/docs/Configuration.md
index b83a8c30..c28def93 100644
--- a/docs/Configuration.md
+++ b/docs/Configuration.md
@@ -383,6 +383,24 @@ key must carry the scopes `historian:read`, `historian:write`, `historian:tags:w
[`docs/Historian.md`](Historian.md) for the full key reference, the migration note (old Wonderware keys →
gateway keys), and the deployment prerequisites.
+#### `ContinuousHistorization` (recorder + outbox knobs)
+
+Only the knobs; the gateway connection comes from `ServerHistorian`. Full descriptions in
+[`docs/Historian.md` §ContinuousHistorization configuration](Historian.md#continuoushistorization-configuration).
+
+| Key | Default | Meaning |
+|---|---|---|
+| `ContinuousHistorization:Enabled` | `false` | `true` **and** a configured `ServerHistorian` wires the FasterLog outbox and spawns the recorder. |
+| `ContinuousHistorization:OutboxPath` | `""` | **Directory** for the FasterLog segment + commit files. Required when enabled; use an **absolute** path on durable storage. |
+| `ContinuousHistorization:CommitMode` | `PerEntry` | `PerEntry` fsyncs before the append returns; `Periodic` commits on a timer every `CommitIntervalMs`. **`PerEntry` is one fsync per ingest *burst*, not per value** — the recorder appends a burst through `AppendBatchAsync`, which enqueues every entry and issues a single group commit. Durability is unchanged: the call does not return until that commit lands. |
+| `ContinuousHistorization:CommitIntervalMs` | `100` | Periodic-mode cadence (ms); must be `> 0` under `Periodic`. |
+| `ContinuousHistorization:DrainBatchSize` | `1024` | Entries peeked + written per drain pass. **Raised from 64**: the peek is an in-memory scan (widening it costs allocation, not I/O) and the pass is now bounded-parallel rather than sequential, so a wide batch no longer costs `tags × latency`. 64 drew down ≤ 64 entries per `DrainIntervalSeconds`, so any gateway hiccup left the outbox permanently behind, growing toward `Capacity` and shedding oldest samples. |
+| `ContinuousHistorization:DrainIntervalSeconds` | `2` | Steady drain cadence (and post-success reschedule). |
+| `ContinuousHistorization:DrainConcurrency` | `8` | Historian tags one drain pass writes **concurrently** — a batch is grouped per tag and each group is its own gateway round-trip, so this turns a sequential `tags × latency` pass into `⌈tags / concurrency⌉ × latency` while bounding outstanding round-trips. `1` = fully sequential; `< 1` is clamped to 1 with a `Validate()` warning. The ack is unchanged (all-or-nothing after every group reports), as is the #538 quarantine rule. |
+| `ContinuousHistorization:Capacity` | `500000` | Max un-acked entries before drop-oldest; `0` = unbounded. The #538 disk backstop for a historian refusing **every** write — the one case the per-tag quarantine cannot resolve. |
+| `ContinuousHistorization:MaxWriteAttempts` | `5` | #538 poison-tag budget: consecutive failed passes one tag may accumulate — **counted only across passes where *other* tags wrote successfully** — before its entries are abandoned so the FIFO head can advance. |
+| `ContinuousHistorization:MinBackoffSeconds` / `MaxBackoffSeconds` | `1` / `30` | Initial and capped exponential retry backoff after a failed drain pass. |
+
### `LocalDb` (pair-local config cache — driver role only)
Driver-role nodes keep a consolidated **`ZB.MOM.WW.LocalDb`** SQLite database that caches the deployed
diff --git a/docs/Historian.md b/docs/Historian.md
index 1d360b87..02b0919a 100644
--- a/docs/Historian.md
+++ b/docs/Historian.md
@@ -142,6 +142,47 @@ source it from there.
---
+## ContinuousHistorization configuration
+
+`ContinuousHistorizationOptions` binds the `ContinuousHistorization` section. It carries **only** the
+recorder + outbox knobs — the gateway connection (endpoint / key / TLS) is sourced from
+`ServerHistorian` (above), never restated here.
+
+| Key | Type | Default | Description |
+|---|---|---|---|
+| `Enabled` | bool | `false` | `true` **and** a configured `ServerHistorian` wires the FasterLog outbox + gateway value-writer and spawns the `ContinuousHistorizationRecorder`. `false` → no recorder; driver tag values are not historized. |
+| `OutboxPath` | string | `""` | **Directory** holding the FasterLog segment + commit files. Required when `Enabled`. In production set an **absolute** path on durable storage — a relative path resolves against the host's working directory. |
+| `CommitMode` | string | `PerEntry` | `PerEntry` fsyncs before the append returns (no loss window); `Periodic` batches commits onto a background timer every `CommitIntervalMs`. Parsed case-insensitively; an unrecognized value falls back to `PerEntry`. **See the batch-commit note below — `PerEntry` is one fsync per ingest *burst*, not per value.** |
+| `CommitIntervalMs` | int | `100` | Periodic-mode commit cadence (ms); must be `> 0` under `Periodic`, ignored under `PerEntry`. |
+| `DrainBatchSize` | int | `1024` | Outbox entries peeked + written per drain pass. **Raised from 64**: the peek is an in-memory scan of the outbox's live index (widening it costs allocation, not I/O), and a pass is now bounded-parallel over `DrainConcurrency` rather than sequential, so a wide batch no longer costs `tags × latency`. At 64 a drain drew down at most 64 entries every `DrainIntervalSeconds` — below the arrival rate of even a modest historized tag set — so any gateway hiccup left the outbox permanently behind, growing toward `Capacity` and shedding oldest samples instead of catching up. |
+| `DrainIntervalSeconds` | double | `2` | Steady drain cadence (and the post-success reschedule). |
+| `DrainConcurrency` | int | `8` | Historian tags a single drain pass writes **concurrently**. One peeked batch is grouped per historian tag and each group is an independent gateway round-trip, so a sequential pass cost `tags × latency`; this window makes it `⌈tags / concurrency⌉ × latency` while bounding how many round-trips can be outstanding against the gateway at once. `1` restores the fully sequential drain; a value `< 1` is clamped to 1 (with a `Validate()` warning). **The ack is unchanged** — still all-or-nothing after every group has reported, and the #538 per-tag quarantine still keys on "another group wrote this pass". |
+| `Capacity` | int | `500000` | Max un-acked outbox entries before the drop-oldest policy sheds the front of the queue; `0` = unbounded. Roughly 50 MB of FasterLog. The #538 **disk backstop** for the one case the per-tag quarantine deliberately cannot resolve — a historian unreachable or refusing *every* write, where nothing proves any particular tag is at fault so the recorder correctly retains. |
+| `MaxWriteAttempts` | int | `5` | #538 poison-tag budget: consecutive failed drain passes one historian tag may accumulate before its queued entries are abandoned and the FIFO head is allowed to advance. **Counted only across passes where *other* tags wrote successfully**, so an ordinary gateway outage never advances it. Clamped to at least 1; each abandonment logs a Warning naming the tag. |
+| `MinBackoffSeconds` | double | `1` | Initial retry backoff after a failed drain pass. |
+| `MaxBackoffSeconds` | double | `30` | Cap on the exponential retry backoff. |
+
+> **`PerEntry` now means one fsync per ingest *burst*, not per value.** The recorder appends a whole
+> value burst through `IHistorizationOutbox.AppendBatchAsync`, which enqueues every entry and then
+> issues a **single** group commit — so a burst of N values costs one fsync rather than N. The
+> durability contract is unchanged: the call does not return until that commit completes, so nothing
+> the caller has been told is buffered can be lost to an unclean restart. (The documented residual is
+> unchanged too: a throw *before* the commit leaves the enqueued prefix tracked-but-uncommitted —
+> served correctly for the life of the process, absent after an unclean restart — exactly the
+> enqueue-then-commit window the single-entry path always had, widened from one entry to the batch.)
+
+> **Cross-repo follow-up — a multi-tag batch `WriteLiveValues` on the gateway contract.** The drain's
+> unit of work is one gateway round-trip **per historian tag**, because
+> `ZB.MOM.WW.HistorianGateway.Client` **0.3.0** exposes no RPC that writes values for more than one tag
+> in a call. Bounded parallelism (`DrainConcurrency`) is therefore the ceiling: it overlaps the
+> round-trips but cannot remove them, so a wide tag set still pays `⌈tags / concurrency⌉` network
+> hops per drain pass. Collapsing that to a single hop needs a **batch/multi-tag `WriteLiveValues`** on
+> the `historian_gateway.v1` contract in the `~/Desktop/HistorianGateway` sister repo. Until that
+> lands, raising `DrainBatchSize` widens each hop's payload but not the hop count — which is why the
+> concurrency window, not the batch width, is what governs drain throughput today.
+
+---
+
## A poison tag no longer pins the outbox (#538)
`DrainOnceAsync` peeks a batch, writes **every** per-tag group in it, and then acks **all-or-nothing** —
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Host/appsettings.json b/src/Server/ZB.MOM.WW.OtOpcUa.Host/appsettings.json
index a1392094..d40730a8 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Host/appsettings.json
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Host/appsettings.json
@@ -43,10 +43,17 @@
"OutboxPath": "",
"_OutboxPathComment": "Directory holding the FasterLog segment + commit files. Required when Enabled=true. In production set an ABSOLUTE path on durable storage.",
"CommitMode": "PerEntry",
+ "_CommitModeComment": "PerEntry means one fsync per ingest BURST, not per value: the recorder appends a whole burst through AppendBatchAsync, which enqueues every entry and issues a single group commit. Periodic batches commits onto a timer every CommitIntervalMs (bounded loss window).",
"CommitIntervalMs": 100,
- "DrainBatchSize": 64,
+ "DrainBatchSize": 1024,
+ "_DrainBatchSizeComment": "Entries peeked + written per drain pass. Was 64 when a pass wrote its per-tag groups sequentially; the peek is an in-memory scan and the pass is now bounded-parallel over DrainConcurrency, so a wide batch is cheap — and 64 let the outbox fall permanently behind during any gateway hiccup.",
"DrainIntervalSeconds": 2,
- "Capacity": 0,
+ "DrainConcurrency": 8,
+ "_DrainConcurrencyComment": "Historian tags a single drain pass writes concurrently (one gateway round-trip per tag group). 1 restores the fully sequential drain. The ack is unchanged: still all-or-nothing after every group reports.",
+ "Capacity": 500000,
+ "_CapacityComment": "Max un-acked outbox entries before drop-oldest; 0 = unbounded. The Gitea #538 disk backstop for a historian refusing EVERY write — the one case the per-tag quarantine cannot resolve.",
+ "MaxWriteAttempts": 5,
+ "_MaxWriteAttemptsComment": "Gitea #538: consecutive failed drain passes one tag may accumulate — counted only across passes where OTHER tags wrote successfully — before its queued entries are abandoned so the FIFO head can advance.",
"MinBackoffSeconds": 1,
"MaxBackoffSeconds": 30
},
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Historian/ContinuousHistorizationOptions.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Historian/ContinuousHistorizationOptions.cs
index 25fc806f..a690835b 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Historian/ContinuousHistorizationOptions.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Historian/ContinuousHistorizationOptions.cs
@@ -43,6 +43,15 @@ public sealed class ContinuousHistorizationOptions
/// every ms (higher throughput, a bounded worst-case loss window).
/// Parsed case-insensitively against HistorizationCommitMode; an unrecognized value falls
/// back to PerEntry.
+ ///
+ /// PerEntry now means one fsync per ingest burst, not per value. The
+ /// recorder appends a whole value burst through
+ /// IHistorizationOutbox.AppendBatchAsync, which enqueues every entry and then issues a
+ /// single group commit — so a burst of N values costs one fsync instead of N. The
+ /// durability contract is unchanged: AppendBatchAsync does not return until that
+ /// commit completes, so nothing the caller has been told is buffered can be lost to an
+ /// unclean restart.
+ ///
///
public string CommitMode { get; init; } = "PerEntry";
@@ -50,9 +59,23 @@ public sealed class ContinuousHistorizationOptions
/// is Periodic. Ignored under PerEntry.
public int CommitIntervalMs { get; init; } = 100;
- /// Maximum outbox entries peeked + written per drain pass; clamped to a positive value by
- /// the recorder (a non-positive value falls back to 64).
- public int DrainBatchSize { get; init; } = 64;
+ ///
+ /// Maximum outbox entries peeked + written per drain pass; clamped to a positive value by the
+ /// recorder (a non-positive value falls back to the default).
+ ///
+ /// Defaults to 1024. It was 64 when a pass wrote its per-tag groups sequentially, so
+ /// a wide batch cost tags × latency on the drain thread. Both halves of that reasoning
+ /// are gone: the peek is an in-memory scan of the outbox's live index (widening it costs
+ /// allocation, not I/O), and the pass is now bounded-parallel over
+ /// , so its cost is ⌈tags / concurrency⌉ × latency
+ /// regardless of batch width. At 64, a drain draws down at most 64 entries every
+ /// — below the arrival rate of even a modest historized
+ /// tag set — so any gateway hiccup left the outbox permanently behind, growing toward
+ /// and shedding oldest samples, rather than catching up once the
+ /// gateway recovered.
+ ///
+ ///
+ public int DrainBatchSize { get; init; } = 1024;
/// Steady drain cadence in seconds (also the post-success reschedule). Defaults to 2.
public double DrainIntervalSeconds { get; init; } = 2;
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/ContinuousHistorizationOptionsTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/ContinuousHistorizationOptionsTests.cs
index 58c64674..b3d3e7a3 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/ContinuousHistorizationOptionsTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/ContinuousHistorizationOptionsTests.cs
@@ -36,6 +36,26 @@ public sealed class ContinuousHistorizationOptionsTests
}.Validate(),
m => m.Contains("CommitIntervalMs"));
+ ///
+ /// Pins the shipped defaults, which are a tuned set rather than arbitrary numbers: the drain is
+ /// bounded-parallel over an in-memory peek (so a wide DrainBatchSize is cheap and a narrow
+ /// one lets the outbox fill during a gateway hiccup), Capacity is the #538 disk backstop,
+ /// and MaxWriteAttempts is the #538 poison-tag budget. The shipped
+ /// appsettings.json restates these values, so a silent drift between the two is exactly
+ /// what this test exists to catch.
+ ///
+ [Fact]
+ public void Defaults_are_the_documented_batch_era_values()
+ {
+ var options = new ContinuousHistorizationOptions();
+
+ Assert.Equal("PerEntry", options.CommitMode);
+ Assert.Equal(1024, options.DrainBatchSize);
+ Assert.Equal(8, options.DrainConcurrency);
+ Assert.Equal(500_000, options.Capacity);
+ Assert.Equal(5, options.MaxWriteAttempts);
+ }
+
/// A fully-configured enabled recorder produces no warnings.
[Fact]
public void Valid_config_is_clean()