greptimedb/tests/perf/query_cases/sst_float_bss/RESULTS.md

SST float BSS: mixed-data post-flush evidence

This report replaces the earlier unique-integer experiment as the primary evidence for sst_float_bss. The detailed historical numbers remain in Git history; they apply only to that superseded workload and must not be used for the current mixed case.

Timing measurements are confounded. After these runs, the user reported that other agents' builds saturated all 20 logical CPUs during measurement. No host-wide idle/load gate was enforced. The latency tables below are retained as raw observations only: neither improvements nor threshold failures establish BSS performance. SST byte counts and cross-target stored-row checks remain valid for the inspected dataset. Stable-host timing verification is pending.

Case and data shape

• Generator/case revision: 149b49de5f3.
• Base and candidate used the same release greptime binary. The only physical table difference was experimental_sst_float_field_encoding: default versus byte_stream_split; base used dictionary encoding and candidate used BSS without dictionaries. This is not a dictionary-policy-held-constant comparison.
• Each of three fresh post-flush runs wrote 1,000 series × 4,320 samples at 60-second intervals: 4,320,000 rows per target. Three explicit flushes produced six SSTs per target: three × 1,105,920 rows and three × 334,080 rows, with 45 greptime_value row groups total. This is observed layout, not a layout guarantee.
• bounded_mixed is a synthetic, uncalibrated design: a series hash selects its baseline and span band, and 60-sample anchor interpolation produces bounded fluctuation. It does not represent a measured production distribution.
• Exactly 950 equal-length series are integer-only and 50 are fractional-only, yielding 4,104,000 integer rows and 216,000 fractional rows per target. The equal-length 1,000-series design deliberately makes both the series and row shares 95%/5%.
• The 95% design is not an empirical claim. A local preview survey project observed 94.79% integral samples; it does not establish a global rate, global uniqueness, or a 95% series distribution.

Initial SST inspection and value verification

Inspection is limited to data/greptime/public; bytes exclude WAL, indexes, metadata, and internal/private-table storage. Each of the three runs had the same totals:

Measure	Default	BSS	BSS change
Selected SST bytes	20,443,131	8,884,743	-56.5392%
greptime_value compressed bytes	20,201,188	8,643,964	-57.2106%
SST files / rows / value row groups	6 / 4,320,000 / 45	6 / 4,320,000 / 45	—

Footer inspection found PLAIN/RLE/RLE_DICTIONARY for the default value column and RLE/BYTE_STREAM_SPLIT for BSS (both ZSTD level 1). The configured storage threshold remains a 5% reduction; this repeated SST-size result passes that threshold. It is post-flush evidence only, not a compaction result or a general float-compression claim.

For every base/candidate group in all three runs, rows were compared by the same primary key and timestamp and their Float64 bits were exact matches: 950 integer-only and 50 fractional-only series, 4,104,000 and 216,000 rows respectively. The six canonical sorted-row SHA-256 results are identical:

48f87d7d01bc8a0ce9a9cdb3033f322e787784fcae61f1417ac25b05c4a40375

This verifies exact cross-target stored rows, not independent reconstruction of the generator output. All 1,000 series had both rises and falls, and every one of the 36 inspected SSTs contained both integer-valued and fractional values; these were not stored as two disjoint file sets.

Warmed endpoint SQL

Each query used three warmups followed by 15 measured endpoint requests. Values are median/p95 milliseconds; delta is (BSS median - default median) / default median × 100%. The guardrail remains a maximum 25% candidate median regression and was not changed for these runs.

Run	Query	Default median / p95	BSS median / p95	Delta	Guardrail
mixed-1	sum_all_values	27.13 / 37.38	25.45 / 38.99	-6.21%	pass
mixed-1	hourly_sum_values	118.78 / 136.63	130.93 / 185.26	+10.23%	pass
mixed-2	sum_all_values	24.02 / 35.02	36.34 / 56.01	+51.31%	fail
mixed-2	hourly_sum_values	95.58 / 120.40	85.45 / 148.03	-10.60%	pass
mixed-3	sum_all_values	38.25 / 55.41	19.68 / 29.49	-48.55%	pass
mixed-3	hourly_sum_values	56.77 / 148.29	121.87 / 143.16	+114.66%	fail

The two recorded threshold failures remain in the artifacts, but the saturated shared host prevents attributing them to BSS. Passing entries likewise do not establish performance acceptance. No CPU isolation or cache flush was used.

Stopped-directory warm readers

For each of the three datasets, eight outer rounds alternate base/candidate order. Each command runs eight iterations, discards the first, and takes the median of iterations 2–8. Parquetbench reads every SST: sum the six per-file medians, then take the median of the eight round totals. Scanbench scans the whole region and reports the outer median of its eight warm medians. These are distinct metrics, not interchangeable whole-query latencies. Deltas are ratios of separately aggregated medians. Value projection selects greptime_value; all-column parquetbench returns five physical columns, while scanbench uses {} (all region columns). Projection order is fixed; target order alternates.

Dataset	Projection	Reader	Base ms	BSS ms	Change
mixed-1	value	parquetbench	95.957	68.442	-28.67%
mixed-1	value	scanbench	144.293	115.421	-20.01%
mixed-1	allcolumns	parquetbench	176.620	103.761	-41.25%
mixed-1	allcolumns	scanbench	200.881	202.660	+0.89%
mixed-2	value	parquetbench	112.151	74.275	-33.77%
mixed-2	value	scanbench	109.824	78.189	-28.80%
mixed-2	allcolumns	parquetbench	141.944	102.681	-27.66%
mixed-2	allcolumns	scanbench	211.414	163.261	-22.78%
mixed-3	value	parquetbench	121.827	67.565	-44.54%
mixed-3	value	scanbench	100.968	79.878	-20.89%
mixed-3	allcolumns	parquetbench	113.984	94.361	-17.22%
mixed-3	allcolumns	scanbench	193.101	164.175	-14.98%

All 672 commands / 5,376 raw iterations returned the expected rows; timing, projection configurations, parquet schemas and order metadata were checked. Run 1 all-column scanbench differed by +0.89%, negligible relative to the observed variation, not evidence of a regression. Its round medians ranged from 167.197–663.465 ms (base) and 133.339–557.352 ms (BSS). There is substantial variability; these measurements do not establish a stable gain on every read path. The reported concurrent CPU saturation affects apparent improvements as well as slowdowns; no causal performance conclusion is drawn from these runs.

Scope and recorded checks

This case compares default and BSS post-flush data only. It adds no benchmark framework and no public artifact upload. Historical unique-integer results and other mixed counter/gauge studies have different data and methods; they are context only and do not apply to this workload.

Recorded checks for this change set: 37 targeted Rust tests, 20 Python tooling tests, and 15 plans passed. Full-workspace tests were not run.

Local artifacts are under /mnt/nvme_rust/rust-targets/metric-bss-perf/experiments/mixed-{1,2,3}/, including value-verification.json, verification.txt, and each run's sst_float_bss/query-regression-report.json.

Warm artifacts are in sibling warm-mixed-{1,2,3}/ directories; mixed-warm-comparison.json contains the table and per-round ranges. mixed-file-composition.json records integer/fractional counts for each SST. The shared release greptime SHA-256 is 2ce0ab1670cd4bdb0f60c87af3e1f494ee66c3c6ab83bce943a073638514eb2b.