The Lane H2 remediation made Periodic(100 ms) the options-class default, but
appsettings.json, docker-dev and Program.cs's bad-value fallback all used
PerEntry, so effective behaviour never changed and the docs contradicted the
shipped config. The options default is now PerEntry; Periodic stays opt-in
(<= CommitIntervalMs of crash loss in exchange for throughput). Program.cs now
uses ContinuousHistorizationOptions.ResolveCommitMode() so the fallback shares
the single DefaultCommitMode constant. docs/Historian.md updated.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
Item 1 of #776 (the B2 over-the-wire ask): Client.CLI had no way to issue a
HistoryReadEvents. `historyread --events` now sends ReadEventDetails to an
event notifier and prints one line per event in select-clause order.
--fields picks the select clauses (default EventId, EventType, Time,
SourceName, Severity, Message, ConditionName (on ConditionType), SourceNode);
--of-type adds an OfType where-clause. --events is exclusive with --modified /
--aggregate, and --fields / --of-type require it.
Client.Shared gains IOpcUaClientService/ISessionAdapter.HistoryReadEventsAsync
(default-implemented as NotSupported for other implementations) backed by the
real session adapter through HistoryReadPaging, so continuation points are
followed up to --max and a Bad node status is surfaced, not printed as empty.
Tests: CLI tests over the fake service (default filter, --fields/--of-type
filter, option conflicts); an over-the-wire test drives the shared client's
event read against the in-process server — the default fields come back
non-null, OfType filters, an invalid where-clause is BadEventFilterInvalid.
The other #776 items are decisions and are left open.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
QuestDB modified-history reads dropped every still-pending trail row that was
not the latest at its source time, so V0->V1 (applied marker never written)
followed by V1->V2 hid the V0->V1 change for good. A pending row below the
latest is now served when the NEXT trail row at that time recorded a different
prior value (kind, value, status or the prior's server_ts) - the next change saw
what this one wrote; an orphan of a change that never landed leaves the same
prior for the next row and stays hidden. QuestDB window functions reject
VARCHAR, so the next row's prior comes from a LEFT JOIN on (ts, lead(id)).
The updater's comment and marker-failure log no longer claim modified reads
"still serve it" unconditionally.
Regression tests (QuestDB 10.0.1 throwaway container): marker lost then a
replace / delete at the same time; an orphan followed by a marker-lost retry
then a later change (orphan still dropped); the random marker-mix fuzz now
varies the recorded priors. All four fail on the old filter.
NITs:
- SqlServerHistorianValueWriter: a SqlException raised while the token is
cancelled (SqlClient's "Operation cancelled by user") is rethrown as
OperationCanceledException instead of booked as a failed write. Integration
test holds a TABLOCKX on Sample and cancels mid-INSERT; it returned false before.
- SqlServerHistorianDataUpdater.DeleteRawBatches is an Interlocked counter.
- HistoryReadEvents: an event filter whose SDK validation throws (unknown
operator) failed with the generic BadUnexpectedError; the node manager now
re-throws any failed event-filter validation as BadEventFilterInvalid.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
HistoryReadEvents projected only EventId / SourceName / Time / ReceiveTime /
Message / Severity: a select clause asking for EventType, ConditionName or
SourceNode (what most generic alarm viewers ask for) got nulls, and the
event filter's where-clause (an OfType) was ignored.
- HistoricalEvent gains optional EventTypeName, ConditionName and AlarmId.
SqlServer, QuestDB and Gateway event reads fill them from what their
alarm writers already store (AlarmTypeName / AlarmName / AlarmId; the
gateway event Type and its AlarmName / AlarmId properties).
- The node manager maps the type name to its Part 9 event type (unknown or
non-event => AlarmConditionType), projects ConditionName, and resolves
SourceNode to the materialised condition the alarm id names (the live
events' SourceNode), else null.
- The where-clause is evaluated per event with the SDK content filter
through an IFilterTarget (OfType via the type tree; other operators
against the projected fields), after the page's cursor is taken, so
paging is unchanged.
Tested in the node manager, over a real client session (the Client.CLI has
no `historyread --events` mode yet; filed as a follow-up), and by alarm
writer -> event read round trips on SqlServer and QuestDB.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
The Gateway backend's gaps against SqlServer/QuestDb were documented
piecemeal. The backend-selection table in docs/Historian.md now also covers
the aggregate set (and the native time-weighted opt-in), emulated reverse
and end-only reads, the client-side events cap, retention and the health
probe.
Continuous historization on Gateway silently loses sample quality (stored
Good), comms-loss outage markers and non-numeric values. Building its live
writer, which only happens when ContinuousHistorization is enabled, now
logs one startup Warning that names the gaps and the alternatives.
The review asked for the matrix in the AdminUI backend picker, but no such
picker exists: the backend is configuration-only. Filed as a follow-up.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
The continuous-historization recorder awaited every outbox append (an fsync
under PerEntry) on its mailbox, so ingestion was capped at 1/fsync_latency
bursts per second while the mux kept telling into an unbounded, unmetered
mailbox. GetStatus also suspended the mailbox on an unbounded outbox count.
- Gated ingest bursts go to a bounded channel (64 bursts) drained by one
ordered append loop, which commits every burst waiting behind a slow
append in a single AppendBatchAsync (FIFO kept). Only a full queue holds
the mailbox (backpressure, bounded memory). Counters are Interlocked; the
loop nudges the drain. PostStop flushes queued bursts within the shared
5 s stop budget.
- GetStatus reads counters on the actor thread and pipes a count bounded by
a 10 s timeout (-1 when it does not answer); it no longer suspends the
mailbox. RecorderStatus gains PendingAppends, MailboxDepth and
AppendBackpressureWaits; two gauges publish pending appends and mailbox
depth.
- ContinuousHistorization:CommitMode defaults to Periodic (100 ms). The
Host's appsettings.json, its unparseable-value fallback and docker-dev
still say PerEntry: filed as a Host follow-up (outside this lane).
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
QuestDB has no multi-table transaction, so a HistoryUpdate writes its trail
row before the sample change. A failed or crashed change left an orphan
trail row that modified reads served as a change that happened, and a trail
INSERT re-sent after a client timeout duplicated (the table had no key).
- sample_modified gains `pending` and DEDUP UPSERT KEYS(ts, tag,
modified_id). The trail row is written pending; after the change lands
the same row is re-upserted pending = false (the applied marker).
- A transient trail INSERT failure is re-sent once with the same ids; a
first attempt that did apply converges on the key.
- ReadModifiedAsync serves a pending row only when it is the latest trail
row at its time and the sample there was written at or after the
modification (a crash between change and marker). The orphan of a change
that never landed, typically followed by the client's retry, is dropped.
ASOF JOIN over the window's samples of one tag; the resume filter sits
outside the window function so it never cuts a time's partition.
- The bootstrapper migrates an older trail (ADD COLUMN pending, DEDUP
ENABLE) and waits for it to apply (bounded 10 s); old rows read
pending = false and stay visible. Until applied, or with
AutoCreateSchema=false, the old format is used.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
DeleteRaw deleted an unbounded range in one statement and transaction with
OUTPUT INTO the modification trail. Over years of a 1 Hz tag that is tens of
millions of rows deleted and audited at once: lock escalation on Sample
(blocking the live writer), transaction-log growth, and a 30 s
CommandTimeout that rolled the whole thing back.
It now runs DELETE TOP (4000) batches, each its own transaction with its
trail rows in the same statement (every deleted row is still audited),
cancellable between batches. A failure part-way leaves the committed batches
deleted and reports the failure; re-issuing completes it (documented, same
as QuestDB's paged tombstoning). The existing atomicity tests still hold per
batch.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
Event reads filtered on source and every modified-value read filtered on tag
scanned that symbol column in every partition of the window; only
sample.tag carried an index (#683).
Both columns are now SYMBOL INDEX in the DDL, and the bootstrapper's index
migration is generalised over QuestDbTables.SymbolIndexes (sample.tag,
event.source, sample_modified.tag): a missing index is added with the same
idempotent ALTER ... ADD INDEX, Warning-only when AutoCreateSchema is false
or the ALTER is refused. Integration tests: new tables carry all three; a
pre-index table set gains them on boot and event reads answer the same.
This reverses #683's documented choice to leave the two unindexed;
docs/Historian.md carries the reasoning.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
The SqlServer purge read every TagId and issued at least one DELETE TOP per
table per tag on every pass, even when nothing was eligible: 50000 tags made
100000 statements per hourly purge, serialised on one connection under the
applock.
One pre-filter query per table (EXISTS seek on the clustered key) now picks
the tags holding a row older than the cutoff; only those get deletes. A pass
with nothing eligible sends just the Event delete. The mid-command
cancellation test now accepts the pre-filter SELECT as the blocked command,
since it is the first statement to touch Sample.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
All three alarm-history writers inserted one event per round trip, serially
(SqlServer also opened a pooled connection per event), so a 10000-event
alarm storm drained at 10000 x RTT while the backlog sat in LocalDb.
- Sql.Common.AlarmBatchWrite: one statement per chunk; a chunk that fails
PermanentFail-class is re-sent event by event so only the poison event
dead-letters; a transient failure retries the chunk; a cancellation never
dead-letters.
- SqlServer: multi-row insert-if-absent over a VALUES set (150 events per
statement, under the 2100-parameter limit), duplicate ids in a batch
written once; a duplicate-key race isolates per event, where it is Ack.
No new table type, so no schema migration (the review suggested a TVP;
the VALUES form gets the same one-round-trip-per-chunk without one).
- QuestDb: multi-row INSERTs of 500 events; pre-1970 events still
dead-letter unsent.
- Gateway: no batch RPC exists, so sends are pipelined, at most 8 in
flight, outcomes kept in input order.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
The QuestDB live writer waited for WAL visibility after every tag group, and
the wait polled wal_tables() every 10 ms. With DrainConcurrency = 8 that was
up to eight pollers at ~100 queries/s each against a database whose WAL
apply was already behind.
New Runtime seam IHistorianPassWriter (WriteLiveValuesInPassAsync +
FlushAsync). The recorder writes every group of a pass through it and calls
FlushAsync once after all groups report, before the ack, whenever any group
wrote (an un-acked pass is redelivered and its insert-if-absent check must
see this pass's rows). A flush failure does not fail the pass. The QuestDB
writer implements it: in-pass writes only mark a flush as owed; FlushAsync
waits once. The poll now backs off 10 -> 20 -> ... -> 200 ms, never past the
timeout. Direct WriteLiveValuesAsync callers still wait per call.
Also updates the QuestDB cancelled-write integration test to the rethrow
contract from the previous commit.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
Every IHistorianValueWriter caught Exception and returned false, including
OperationCanceledException from the drain's own token. The recorder's guard
("a cancelled pass is not a tag failure") was therefore dead code: at shutdown
mid-pass each cancelled group could be booked as a consecutive failure and,
with a sibling that already wrote, tip a healthy tag toward quarantine.
SqlServer, QuestDb and Gateway writers now rethrow a cancellation of the
caller's token; a cancellation-shaped error on a live token is still an
ordinary failed write.
The Gateway writer relabelled a Local-kind timestamp as UTC instead of
converting it, so the same value could land at two different times on two
backends. Stamped samples now go through LiveWritePreparer (Local -> UTC,
non-finite doubles not sent, duplicate timestamps keep the first); unstamped
samples are still left for the gateway to stamp, in batch order.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
Every Gateway HistoryRead was preceded by a BrowseTagNames catalog stream
keyed by a glob filter (a name with '*' or '?' streamed every match), and the
4096-entry presence cache evicted an arbitrary entry (Keys.First()) when full,
so a sweep over more tags thrashed it.
The presence check is now one exact unary GetTagMetadata (null = absent).
Only the deployed gateway's known misparse of a missing tag (Internal /
Unknown / InvalidDataException) falls back to the exact-name catalog check;
any other failure propagates and never becomes absence. The positive TTL is 5
minutes (was 60 s); a full cache drops expired entries first, else the one
closest to expiry. Wire tests cover the working, the misparsing and the
refusing gateway.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
The Gateway historian's ProcessConnectionOpen / EventConnectionOpen were
derived from read outcomes only, so a freshly booted node with a healthy
gateway reported the historian closed until a client read, and a node that
only writes (continuous historization) never flipped it.
The data source now runs a ProbeAsync loop (ServerHistorian:Gateway:
ProbeInterval, default 30 s, first probe at start-up; 0 = off). Each probe,
bounded at 10 s, is recorded as the latest connectivity observation; the
latest observation (probe or read) is what the snapshot reports. Probes never
touch the query/failure counters. DisposeAsync stops the loop before
disposing the client.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
AVEVA's native TimeAverage / Total are answered with Good-status wrong values
while the gateway sends the interval in the wrong unit (historiangw#27): one
whole-span value on the earliest interval, the rest absent. Nothing on the
wire marks the answer as degraded.
Both are now refused BadAggregateNotSupported (unsent, not counted as a
backend failure, not advertised in AggregateFunctions) unless
ServerHistorian:Gateway:EnableNativeTimeWeighted is true. The default
Gateway set is the ten raw-evaluated aggregates
(GatewayHistorianDataSource.RawEvaluatedAggregates); ServedAggregates stays
the 12 the backend can serve with the flag on. The native-path tests opt in.
Also documents the ServerHistorian:Gateway sub-section (EventDrainBudget from
the previous commit) and the events drain in docs/Historian.md.
Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22
in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
The #687/F4 crowding re-read doubled its room up to 8 re-reads with no cap, so a pathological single-ms
cluster on a streaming gateway was streamed several times over for one page. The room is now capped at
ServerHistorian:MaxTieClusterOverfetch (plumbed into GatewayHistorianDataSource as maxPreWindowRows,
default 65536); past it, or once a read has already seen more, the read is BadTooManyOperations with
PreWindowRows set.
Item 1: IHistorianDataSource.MaxRawValuesPerRead (Gateway: learned ceiling - 16 = L; 0 elsewhere, guard-tested).
RawPageLimit plans every raw page on top of #692's lookahead: with L > 0 the read (page P + boundary ties k
+ lookahead) is <= L, P = min(N, L - k - 1) (uncapped: L - k - 1); no room => straight to the tie-cluster
over-fetch (never an uncapped or underflowing request). One re-plan + re-read when the read taught a new
limit or was refused for crowding pre-window rows (HistoryReadLimitExceededException.PreWindowRows): the
page shrinks by them. Over-fetch bound min(MaxTieClusterOverfetch, L - 1); slice size never 0.
Review fixes: F1 a window starting at/before the epoch counts AVEVA's synthetic row as pre-window (a
ceiling-truncated read was reported complete); F2 the page path disables ReverseRawReader's own re-run
(cold end-only ceiling 20/N=3000 cost 3,023 reads, now <= 40); F3 crowded look-back re-read around, not
refused; F4 the #687 crowding re-read room at least doubles (up to 8 re-reads), so a cluster of hundreds
just before a resume point no longer fails on a default gateway; a crowding refusal that leaves no room
is BadTooManyOperations, never a tick-by-tick cursor.
Item 2: ServerHistorian:EventReadHorizon (default 00:00:00 = exact, unchanged). When set, every fresh
HistoryReadEvents window's earlier bound is raised to now - horizon (both directions, all backends).
Lossy by design; documented.
Item 3 (native TimeAverage/Total re-check) stays blocked on historiangw#27.
A time inside a gap of a bursty tag costs a 64-row jump read landing in the next
burst plus a bisection back across the gap (~6 reads), so the 64 + 4/time cap
refused a 1 h/day 1 Hz tag asked at noon on 30/100/300 consecutive days
(186/606/1,806 reads) that AVEVA's own AtTime served. The cap is a runaway guard
(HistoryReadDeadline bounds wall clock): now 64 + 16 per distinct time.
Regression tests for x30/x100/x300 (each <= 7 reads a time, values checked).
Docs: DateTime-hinted nodes are stepped but keep the gateway's Double (the
Gateway never historizes DateTime nodes; the SQL backends return DateTime).
H1: the walk-back reset its width after a full segment and discarded a full
whole-remainder read, so a dense tag that stopped reporting weeks ago gave up
after 65 reads (BadTooManyOperations). It now gallops (x4, whole-remainder read
after two empties) and then BISECTS once any stored row is known below — a full
segment's (incl. a full whole-remainder read's) last row, or an earlier window
read's last row: (mid, hi] empty => hi = mid; full => known = its last row;
complete with rows => done; one density-aimed segment after a full read until an
aimed segment comes back empty; below 2 ms the whole stretch from the known row
(never a 100 ns step). Stopped 1 h..365 d with 5 y history: 6-18 reads at
1/min, 21-25 at 1 Hz, 25-31 at 10 Hz.
M1: a jump read asks for 64 rows (1,000 times over 10 y: ~66k rows, was ~1M).
L1: per-request read cap 64 + 4 x distinct times with a clear message; a strict
ceiling below 4 rows is refused naming the ceiling.
L2: DateTime hints are stepped. L3: under an integer hint a NaN/inf or
out-of-Int64-range value is unusable, never saturated Good.
L5: conformance Int64 AtTime asserts the type. L4: docs name the backend
differences. Nit: the window read end is clamped to now + 1 day.
Reviewer harnesses (Scratch693Fuzz/Cost, not committed): 0 differential diffs
over 2,400 cases.
F1 (pre-existing): SliceTieCluster continued a forward read while next <= endUtc, but the
forward window is end-exclusive; an oversized cluster one step below EndTime resumed AT
EndTime, the resume became a start == end point read and returned the EndTime samples as
data (microsecond: EndTime 8.1 us truncated to 8.0). Continue only while next is strictly
before EndTime truncated to the backend resolution.
Tests: A_tie_cluster_just_below_the_end_time_never_resumes_onto_the_end_time (native +
microsecond; both fail on the old rule) and
A_cursor_inside_a_tie_cluster_over_fetches_without_a_normal_read_first (pins the
WithinTieCluster shortcut by per-page read count; fails with the shortcut disabled).
Docs: the oversized-cluster exception to 'every page full / no lookahead => last' (F2),
and the N + skip + 1 strict-ceiling edge note referencing #694 (F4).
Review follow-up: on the Gateway every value is a Double (AVEVA stores a Boolean
as a 0/1 Int2), so the raw-evaluated AtTime interpolated a Boolean node to 0.5.
- IHistorianDataSource gains a default-interface overload
ReadAtTimeAsync(fullReference, timestamps, TypeCode? valueType, ct) that
forwards to the existing one (SqlServer/QuestDB/Null/fakes unchanged).
- OtOpcUaNodeManager.HistoryReadAtTime passes the node's scalar DataType
(AtTimeValueType: built-in type -> TypeCode; arrays/other types => null);
Raw and UNS NodeIds alike.
- GatewayAtTimeReader converts each raw row to the hinted kind BEFORE the shared
AtTimeEvaluator runs (Boolean = value != 0 => stepped; integers => Int64 =>
interpolated, rounded half away from zero, returned as the node's integer
type; floats Double), so the evaluator's own type branch decides.
- AtTimeEvaluator boxed every interpolated Int64 as a Double (`cond ? (long)x :
v` widens to double); its "keeping its type" test passed because Shouldly
ShouldBe compares numbers across types. Fixed (affects SqlServer/QuestDB too)
and pinned with ShouldBeOfType.
Gateway HistoryRead-AtTime passed AVEVA's own interpolation through: live it
answered the previous value as Good at a stored NULL's own time, null + Bad at
a Good sample right after a NULL, a drifted 99.99999999944 for a stored 100,
and no Interpolated bit. It is now served from raw gateway reads and evaluated
with Sql.Common's AtTimeEvaluator, as the SQL backends do (Part 11 §6.5.4).
GatewayAtTimeReader: one <=1,024-row forward window read [first-1ms, last+1ms]
for the batch, a walk-back (density-seeded, x4 growth, whole-remainder shortcut,
bisects dense history) for the first time's prev, and an 18-row probe for the
last time's next; truncated window reads continue or jump with a density-sized
margin. All bounds whole ms; a row counts only strictly inside its request
(AVEVA's boundary row never a sample); Bad rows value-less (#690); never past
now + 1 day; strict-gateway ceiling learned (#691.3) without re-probing.
10 dense times = 1 read (exact) / 3 (interpolated); 10 hourly = 12.
Kill switch ServerHistorian:GatewayAtTimeFromRaw (default true; false = the
old AVEVA passthrough). Known limit: the wire carries no data type, so numeric
tags interpolate as Double (Boolean/integer nodes are not stepped/rounded as on
the SQL backends).
A tie cluster's truncated read left the width at one tick; once the gap
above it was under two milliseconds nothing floored it, so segHi
stepped down one tick per read: 30 rows at one ms 0.3 s below hi with a
carried 1 s width took 10,006 identical reads (S8). (a) The top-anchored
width is floored at the granularity, Min kept; (b) a segment no wider
than the granularity is the unit that escalates to
MaxTieClusterOverfetch and then refuses - per millisecond, exact for the
ms-resolution Gateway (documented). Both are needed: the floor alone
loops on crowded reads with a small tie budget. S8 is a repo test
(4 shapes, reads <= 30, 0 repeated requests); random-data tests now
measure the refusal unit as rows in any 1 ms window. Reviewer harness,
5,000 seeds x default/MSONLY/CROWD: worst page 70 reads (default/MSONLY),
63 (CROWD) at M=65536, p99.9 27-37; no page over 500 reads at any tie
budget.
Bisecting the gap above a truncated read halved below the 1 ms request
granularity (requests are ms-rounded, so it re-sent identical requests)
and bisected the WHOLE gap even when the burst ended right above the
row it saw: a 1,026-row burst ending 100 days ago took 46 reads. After
an empty top-anchored segment the walk now gallops up from the known
row ((known + d, top], d x4, following each truncated read), then
bisects the bracket, with halving floored at the granularity (the Min
kept; a crowded gallop falls back to top-anchored halving). Burst: 18
reads, 0 repeated requests; dense tag stopped 2 days ago: 26 (gallop
alone crawled: 94). Walk fuzzed at 4,000 seeds locally (400 in-tree).
Docs: measured counts; CLAUDE.md gateway prerequisites list
RuntimeDb:EventReadMaxRows.
GatewayHistorianDataSource.ReadEventsAsync sized its result list to
maxEvents, which is int.MaxValue for NumValuesPerNode = 0: every
uncapped Gateway events read (forward on master, and the new walked
reverse one) threw 'Array dimensions exceeded' and counted as a backend
failure. Capacity is bounded at 1024. The events walk delegate moved to
ReverseEventsReader so it is tested over the real Gateway source
(forward uncapped, reverse uncapped, reverse capped).
A reverse or end-only capped events read on a backend without
SupportsReverseEvents (Gateway, Null) was refused
BadHistoryOperationUnsupported (explicit reverse) or answered with the
OLDEST N ascending (end-only, #675). It is now served newest-first by
the same ReverseWalk as raw reads: page-sized ms-aligned segments,
never answered from a read the source flagged truncated, ties sorted by
EventId (the gateway orders by event time only - the fake shuffles
them per call), one extra event walked to signal 'more', uncapped = one
forward read reversed, and the width + proven-empty stretch carried in
the events cursor. The oversized-cluster over-fetch keeps exactly the
events at T in the same order. A tie cluster over the budget is
BadTooManyOperations. Docs note the gateway's EventReadMaxRows must be
unlimited (it truncates silently).
The last pages of a deep reverse page-through on a forward-only backend
each walked down to 1970 one x4 growth step at a time (~14-16 reads,
~2.5 s live). After two empty segments the walk now asks once per page
for the whole remainder at the page budget (a truncated answer is
discarded and the walk carries on), and the stretch the page's last
complete read proved empty rides the continuation point
(HistoryContinuationState.EmptyFromTicks/EmptyToTicks, session-held, so
no versioning) so the next page steps over it. Fuzz now pages with the
walk's own hints and with true random empty stretches.
ReverseRawReader aimed every segment at half of MaxTieClusterOverfetch
(~32k rows by default) and carried that width page to page, so a paged
'latest N' read on a dense Gateway tag fetched ~32,770 rows per page
(2-5 s live) to return N. The walk now lives in a generic ReverseWalk
core: segments are aimed at ~N+8 rows (page budget 2N+16), a discovery
segment (first without a hint / after an empty one) may read 1,024, and
the tie budget is only the ceiling a single-timestamp cluster escalates
to. A truncated read never re-enters the stretch below its newest row
until the gap above it is bisected. Tests: per-page row counts on a
dense tag (node manager + walk), randomized exactness fuzz (walk and
node-manager paging), dense-tag-below-a-long-gap read bound.
With StartTime at or before the epoch, RequestStartFor has no margin left, so
AVEVA's synthetic no-data/boundary row is stamped exactly at StartTime and was
kept: raw reads returned a fabricated Bad sample at 1970-01-01 and the per-sample
aggregates put it in bucket 0 (Start/End fabricated, Min/Max status Uncertain).
IsWindowSample and the aggregate loop now drop any row with t <= ProbeFloor
(RawAggregateReader.IsAfterFloor), matching the #686 walk-back's assumption.
- M1/M2: when the 1 ms pre-window margin (boundary row + stored samples, e.g. a
>16-sample tie cluster at start-1ms / lastTs-1ms) uses up the cap + 16 budget,
re-read ONCE asking for cap + m + 16 (m = pre-window rows seen); fail
BadTooManyOperations only if the re-read is still short because of them. The
raw budget is no longer clamped at the gateway default ceiling (AVEVA always
emits the boundary row, so page sizes 999,985-1,000,000 always came back
short); the #688 clamp stays on the per-sample aggregate path only.
- Merge trap: NumValuesPerNode 0 => int.MaxValue, never through the clamp.
- L3: the forward end is exclusive ([start, end), the IHistorianDataSource
contract); a point read (start == end, the tie-cluster over-fetch) inclusive.
- RequestStartFor never goes before the Unix epoch (#686's walk-back floor).
- L4 (docs): an Uncertain native row for an all-NULL interval is unverified live.
The default MaxTimeWeightedRawRows (1,000,000) + 18 exceeded the gateway's
default MaxValuesCeiling (1,000,000), so with AllowStreamingBeyondCeiling=false
every Gateway per-sample aggregate read was refused. The allowance is now clamped
at 1,000,000 while the cap is at or under it (RawAggregateReader.
ClampToGatewayCeiling); a cap above it keeps its allowance. Raw reads are not
clamped (rebased onto #686).
An AVEVA Full raw read leads with a row stamped at the query start (the value in
effect, Quality=133, or a no-data NULL row); it was returned as a stored sample.
Raw reads now use the #681 classification (RawAggregateReader.RequestStartFor /
IsWindowSample — one authority, by timestamp, since a stored NULL looks the same
on the wire): request from 1 ms early with NumValuesPerNode + 16 rows, keep rows
at or after StartTime, drain the whole stream. A full page still holds exactly
the cap, so #669 paging/resume/tie-cluster reads are unchanged; a margin that
swallows the allowance fails the node rather than ending paging early.
ReturnBounds is not plumbed on any backend (documented).
AVEVA answers one extra row for the interval before the window; it was mapped as
a result stamped before StartTime (N+1 values). Rows whose interval lies outside
the requested span (either direction) are now dropped after the drained stream.
An Uncertain (opc 64-191) interval kept no value (opc >= 192 was the only data
test); it now carries its value as UncertainDataSubNormal | Calculated.
Docs: AVEVA's TWA excludes NULL-gap time while the SQL backends bridge it;
end-to-end per-interval values also need historiangw#27.
Joseph Doherty