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perf(historian): index the QuestDB sample tag column; read the data range before the buckets (#683)

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QuestDB: {p}sample.tag is now SYMBOL INDEX. The processed-read data-range
lookups (EarliestSample / LatestSample) were partition scans of the unindexed
symbol; on 53.6M rows / 120 tags / 61 daily partitions the indexed seeks are
1-1.5 ms warm / 2-4 ms cold whatever the tag's history (unindexed: up to 11 ms
warm, 14 ms cold; cost grew with the table). The bootstrapper adds the index to a
pre-#683 table (ALTER ... ADD INDEX, a WAL txn, idempotent, ~3 s for 68M rows);
AutoCreateSchema=false only logs the statement. Disk +~12%; write apply time
within noise; main per-sample/raw/time-weighted queries unchanged or faster.

Rejected by measurement/analysis: bounded existence probes (still full scans
when a side is absent), LATEST ON (slowest unindexed), per-tag first/last side
table (cannot track TTL drops or deletes INSERT-only).

Both backends now read the data range before the bucket statement: an append
racing the read reaches the buckets but not the range, so it can no longer
produce a Good Count of 0 for an interval that has samples.

Tests: TagIndexTests (new-table index, bound-param seek uses the index,
tombstones excluded / outage marker counted, pre-#683 migration with identical
processed results across 10 aggregates x 4 windows x both directions).
This commit is contained in:
Joseph Doherty
2026-10-12 09:40:28 -04:00
parent 197246c3c1
commit 549d2d68b3
9 changed files with 331 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.SqlServer/SqlServerHistorianDataSource.cs
+16 -9
View File
@@ -462,10 +462,13 @@ public sealed class SqlServerHistorianDataSource : IHistorianDataSource
AggregateFamily.StartEnd => SqlAggregateQueries.StartEnd(sample, plan.Reversed),
_ => SqlAggregateQueries.ActualTime(sample, aggregate == HistoryAggregateType.MaximumActualTime, plan.Reversed),
};
// Second result set: the tag's data range (earliest + latest sample) — the start/end-of-data Partial rules
// (#677/#680 — any per-sample aggregate but Average, either direction) and Count's in-range empty interval (#680).
// FIRST result set when needed: the tag's data range (earliest + latest sample) — the start/end-of-data Partial
// rules (#677/#680 — any per-sample aggregate but Average, either direction) and Count's in-range empty interval
// (#680). Read before the bucket statement (#683): under READ COMMITTED the two statements can see different
// rows, and a sample appended in between must reach the buckets rather than only the range — the opposite
// order turned such a bucket into a Good Count of 0.
var needsRange = AggregateEvaluator.NeedsDataRange(aggregate, plan);
if (needsRange) sql += " " + SqlAggregateQueries.DataRange(sample);
if (needsRange) sql = SqlAggregateQueries.DataRange(sample) + " " + sql;
await using var conn = await _conn.OpenAsync(cancellationToken).ConfigureAwait(false);
await using var cmd = _conn.CreateCommand(conn, sql);
cmd.Parameters.Add(new SqlParameter("@id", SqlDbType.Int) { Value = id });
@@ -474,14 +477,18 @@ public sealed class SqlServerHistorianDataSource : IHistorianDataSource
cmd.Parameters.Add(new SqlParameter("@intervalTicks", SqlDbType.BigInt) { Value = plan.IntervalTicks });
cmd.Parameters.Add(new SqlParameter("@bucketAdjustTicks", SqlDbType.BigInt) { Value = plan.BucketIndexAdjustTicks });
await using var reader = await cmd.ExecuteReaderAsync(cancellationToken).ConfigureAwait(false);
if (needsRange)
{
if (await reader.ReadAsync(cancellationToken).ConfigureAwait(false))
{
if (!reader.IsDBNull(0)) earliest = SqlHistorianConnection.GetUtc(reader, 0);
if (!reader.IsDBNull(1)) latest = SqlHistorianConnection.GetUtc(reader, 1);
}
if (!await reader.NextResultAsync(cancellationToken).ConfigureAwait(false))
throw new InvalidOperationException("The processed-read batch returned no bucket result set.");
}
while (await reader.ReadAsync(cancellationToken).ConfigureAwait(false))
rows.Add(ReadBucket(reader, family));
if (needsRange && await reader.NextResultAsync(cancellationToken).ConfigureAwait(false)
&& await reader.ReadAsync(cancellationToken).ConfigureAwait(false))
{
if (!reader.IsDBNull(0)) earliest = SqlHistorianConnection.GetUtc(reader, 0);
if (!reader.IsDBNull(1)) latest = SqlHistorianConnection.GetUtc(reader, 1);
}
}
var result = AggregateEvaluator.EvaluateAll(aggregate, plan, rows, earliest, latest, now);