d9568e415754516b14bff72b0daf67a0f7f69999
braney
  Tue May 12 16:53:34 2026 -0700
quickLiftBench: add nSweep + posSweep orchestrators and paper Table 1, refs #37445

nSweep.py rebuilds testHub at each (N, BW_STEP) point and runs the bench,
tagging every row with N + bw_step so the merged sweep.tsv plots
"quickLift overhead vs feature count". buildTestHub.sh now also takes a
FEATURE_W env var so the BED12 block model scales down at high N
(auto-picked by nSweep so requested N fits the region without overlap).

posSweep.py mirrors the orchestrator shape but varies the viewed window
on a fixed hub; built-in canonical positions cover 0..5000 in-window
features against the default testHub.

paper_table1.md collects the headline Mode C cells from the
2026-05-12 N + position sweeps: bigBed quickLift ratio scales 4.3x ->
10.3x with feature count, bigWig stays flat ~5x; sparse windows show
near-zero quickLift overhead.

diff --git src/utils/qa/quickLiftBench/README.md src/utils/qa/quickLiftBench/README.md
index dd0eab6c151..1027c91bea1 100644
--- src/utils/qa/quickLiftBench/README.md
+++ src/utils/qa/quickLiftBench/README.md
@@ -1,231 +1,309 @@
 # quickLiftBench
 
 Benchmark suite that compares hgTracks render times for two saved sessions on
 the same server. The intended pairing is a **native** session (tracks rendered
 on their source assembly) against a **lifted** session (the same tracks
 rendered on a different assembly via quickLift). Output TSVs are intended as
 the raw numbers behind tables and figures in a quickLift performance paper.
 
 ## What it measures
 
 For each benchmark case, two (or more) named variants — typically `native`
 and `lifted` — are timed across multiple iterations. Each request loads a
 saved session into a fresh cart and asks hgTracks for the per-request timing
 breakdown. The session renders at the position it was saved with; the runner
 does **not** override `position`, since native and quickLifted variants live
 on different assemblies and the same chr:start-end is not biologically
 equivalent across them. To benchmark multiple regions, save additional
 session pairs and add them as separate cases.
 
 Each response is parsed for:
 
 - **Overall total time** — the headline number, taken from the
   `<span class='timing'>Overall total time: NNN millis</span>` footer span.
 - **Per-track load and draw times** — summed across all visible tracks from
   the `printTrackTiming()` table emitted into a `<span class='trackTiming'>`
   block.
 - **HTTP wall time** — measured around the request itself.
 
 Each variant cell does `warmup` discarded requests followed by `iterations`
 recorded requests. Min / median / p90 are reported.
 
 ## Usage
 
 ```
 ./quickLiftBench.py [--config FILE] [--cases ID,ID]
                     [--server-override NAME]
                     [--iterations N] [--warmup N]
                     [--out DIR] [--verbose] [--phases]
 ```
 
 Defaults: read `cases.yaml` next to the script, no server override, all
 cases, iterations and warmup from `defaults`, output to
 `./results/<timestamp>/`.
 
 Examples:
 
 ```
 # Run everything against the server in each case stanza:
 ./quickLiftBench.py
 
 # One case, against the sandbox, 10 iterations:
 ./quickLiftBench.py --cases bench1_hgwdev \
                     --server-override sandbox --iterations 10
 
 # Quick smoke against a single existing saved session:
 ./quickLiftBench.py --cases smoke_session --iterations 1 --warmup 0 -v
 ```
 
 ## Config schema
 
 ```yaml
 defaults:
   iterations: 5
   warmup: 1
   timeout: 60
   servers:
     hgwdev: https://hgwdev.gi.ucsc.edu
     sandbox: https://hgwdev-braney.gi.ucsc.edu
     beta:   https://hgwbeta.soe.ucsc.edu
     rr:     https://genome.ucsc.edu
 
 cases:
   - id: case_id
     description: "..."
     server: hgwdev          # one server for all variants in this case
     variants:
       native: User/sessionName_native     # user/sessionName
       lifted: User/sessionName_lifted
     compare:
       - [native, lifted]
 ```
 
 Each variant value is one of:
 
 - **Saved-session reference** (string `user/sessionName`, or the equivalent
   `/s/<user>/<name>` short-link form). The session's saved position and
   cart are used. Best for Mode A and Mode B cases where the native and
   lifted variants sit on different assemblies and "the same position" is
   not biologically meaningful.
 
 - **Hub variant** (mapping with `hubUrl`, `db`, `position`, `tracks`).
   Attaches a hub at an explicit db and position, then turns each track
   on/off according to `tracks`. Used for Mode C where both variants live
   on the same assembly and differ only in track visibility. Example:
 
   ```yaml
   variants:
     native:
       hubUrl: https://example.org/myHub/hub.txt
       db: hs1
       position: chr22:15000000-50000000
       tracks: {modeC_native: pack, modeC_lifted: hide}
     lifted:
       hubUrl: https://example.org/myHub/hub.txt
       db: hs1
       position: chr22:15000000-50000000
       tracks: {modeC_native: hide, modeC_lifted: pack}
   ```
 
   The runner sends `hideTracks=1` plus the per-track vis settings so only
   the explicitly named tracks render.
 
 The URL the runner sends per iteration is:
 
 ```
 {server}/cgi-bin/hgTracks?
    hgS_doOtherUser=submit
    &hgS_otherUserName=USER
    &hgS_otherUserSessionName=NAME
    &hgt.trackImgOnly=1
    &measureTiming=1
 ```
 
 Notes on URL choices:
 
 - `hgS_doOtherUser=submit` plus the user/session name causes hgTracks to
   load the saved session into the cart (`cart.c:1715`). The session's saved
   position is used.
 - `hgt.trackImgOnly=1` is the JS-redraw fast path: hgTracks emits the image
   + map and returns without rendering the rest of the page. With
   `measureTiming=1` it also emits the per-track timing block.
 - A fresh `requests.Session()` per case mints a new hgsid (and thus a fresh
   cart) so cases do not contaminate each other.
 
 ## Adding a case
 
 **Saved-session variants** (cross-assembly Mode A / Mode B):
 
 1. Save two sessions on the target server that differ only in the dimension
    you want to measure (typically: native vs. quickLifted versions of the
    same set of tracks). Each session should be saved at the position you
    want it benchmarked at.
 2. Add a stanza to `cases.yaml` using string variants of the form
    `user/sessionName`.
 
 **Hub variants** (Mode C, same assembly + same position):
 
 1. Build (or pick) a hub where two trackDb stanzas reference the same
    conceptual data, one with `quickLiftUrl` and one without. The included
    `testHub/buildTestHub.sh` is a working example: it generates 5000
    synthetic BED12 features on hg38, lifts them to hs1, copies the
    hg38→hs1 quickLift chain in alongside, and writes a 2-stanza hub.txt.
 2. Add a stanza to `cases.yaml` using mapping variants (see schema above).
 
 Either way, smoke-test with `--cases <new_id> --iterations 1 --warmup 0 -v`
 to verify the URL works and timings parse out.
 
+## Density sweep (`nSweep.py`)
+
+`nSweep.py` rebuilds `testHub/` at a sequence of (N, BW_STEP) sizes and runs
+the bench at each one, tagging every row with `N` and `bw_step`. The merged
+`sweep.tsv` is the raw data behind the paper's "quickLift overhead vs.
+density" curve.
+
+```
+./nSweep.py [--n-values 500,1000,5000,10000,20000]
+            [--bw-step-values 1000]
+            [--cases mode_b_bb,mode_b_bw,mode_c_hs1_bb,mode_c_hs1_bw]
+            [--iterations 10] [--warmup 1]
+            [--region-start 15000000] [--region-end 50000000]
+            [--feature-w AUTO]
+            [--hub-dest-base ~/public_html/quickLiftBench/sweep]
+            [--out DIR] [--clean-builds] [--skip-existing] [--dry-run]
+```
+
+Per (N, BW_STEP) point the script:
+
+1. Auto-picks `FEATURE_W` so N features fit in the region without overlap
+   (clamped to [50, 5000]; override with `--feature-w`). Runs
+   `testHub/buildTestHub.sh` with `N`, `BW_STEP`, `FEATURE_W`, and the
+   region bounds into `<hub-dest-base>/N{N}_S{S}_W{W}/`.
+2. Loads `cases.yaml`, filters to `--cases`, rewrites each hub variant's
+   `hubUrl` from `.../testHub/...` to `.../sweep/N{N}_S{S}_W{W}/...`, and
+   drops the rewritten config into the output dir.
+3. Invokes `quickLiftBench.py` with that config; per-point outputs land in
+   `<out>/N{N}_S{S}_W{W}/`.
+4. Appends `results.tsv` to a single `sweep.tsv` with `N` and `bw_step`
+   prepended to each row.
+
+After all points run, `sweep_summary.tsv` has two sections:
+
+- Per (N, bw_step, case, variant): n_ok, total/load/draw median + p90.
+- Per (N, bw_step, case): native vs. lifted total medians and the
+  `lifted/native` ratio — the headline curve.
+
+`--skip-existing` reuses hub dirs that already contain `hub_hs1.txt`, which
+is handy when iterating on bench config without rebuilding identical hubs.
+
+## Position sweep (`posSweep.py`)
+
+`posSweep.py` keeps the hub fixed and varies the *viewed window*, so each
+row measures quickLift overhead at a specific in-window feature density.
+At the default testHub (N=5000 features uniformly distributed across
+chr22:15M-50M at 7kb stride), the built-in canonical positions exercise:
+
+| name | position | in-window features at N=5000 |
+| --- | --- | --- |
+| `sparse` | chr22:1M-2M | 0 (1Mb outside feature region) |
+| `narrow_dense` | chr22:25M-25.1M | ~14 (100kb inside region) |
+| `medium` | chr22:20M-25M | ~714 (5Mb inside region) |
+| `wide` | chr22:15M-50M | ~5000 (full 35Mb region) |
+
+```
+./posSweep.py [--positions name1:chr:start-end,name2:chr:start-end,...]
+              [--cases mode_b_bb,mode_b_bw,mode_c_hs1_bb,mode_c_hs1_bw]
+              [--config cases.yaml]
+              [--iterations 10] [--warmup 1]
+              [--out DIR] [--dry-run]
+```
+
+Per position the script:
+
+1. Loads `cases.yaml`, filters to `--cases`, and rewrites every hub
+   variant's `position` field with the swept position. Saved-session
+   variants are left as-is (the saved session's position can't be
+   overridden) and a warning is printed.
+2. Invokes `quickLiftBench.py`; per-point outputs land in
+   `<out>/<position_name>/`.
+3. Appends `results.tsv` to a single `sweep.tsv` with `position_name` and
+   `position` prepended.
+
+`sweep_summary.tsv` mirrors the N sweep's two-section format: per
+(position_name, case, variant) medians/p90, then per (position_name, case)
+`lifted/native` ratio.
+
 ## Output
 
 Two TSVs are written to `results/<YYYYMMDD-HHMMSS>/`:
 
 - `results.tsv` — one row per (case, variant, iteration) with
   http_ms, load_ms_sum, draw_ms_sum, n_tracks, total_ms, status_code, error.
 - `summary.tsv` — two sections:
   1. per (case, variant): n, n_ok, http/load_sum/draw_sum/total median and p90.
   2. per (case, compare-pair): left vs right total medians and the
      `right/left` ratio for each metric.
 - `phases.tsv` (only with `--phases`) — long-form rows of every
   `<span class='timing'>label: NNN millis</span>` marker emitted by
   hgTracks (chromAliasSetup, trackDbLoad, parallel data fetch, image
   generation, cart write, etc.), one row per (case, variant, iteration,
   phase). A per-(case, variant, phase) median+p90 summary is appended.
   Useful for localizing where time is going when total medians differ.
 
 ## Regression assertions: `phase_asserts`
 
 A case can declare assertions against the per-iteration phase timings, so
 the bench acts as a tripwire for regressions instead of just emitting
 numbers. When any case declares `phase_asserts`, that case's phase data is
 captured automatically (no `--phases` flag needed) and assertions run after
 all iterations complete. A failure prints to stderr and the script exits
 non-zero.
 
 ```yaml
 - id: regress_my_thing
   server: hgwdev
   variants:
     base: User/sessionName
   phase_asserts:
     - variant: base
       phase: 'Waiting for parallel \(\d+ threads for \d+ tracks\) remote data fetch'
       required: true        # span must appear in every iteration
       max_median_ms: 15000  # optional median upper bound
       min_median_ms: 1      # optional median lower bound
 ```
 
 Semantics:
 
 - `phase` is a Python regex matched against each phase label (the part
   before `:` in `<span class='timing'>label: NNN millis</span>`).
 - `required: true` (default) — assert fails if the regex matches no phase
   in any iteration of the variant.
 - `max_median_ms` / `min_median_ms` — optional bounds on the median across
   iterations. Per iteration, all matching phases' ms values are summed,
   then the per-iteration sums are reduced via median.
 - A FAIL prints `[FAIL] case/variant /pattern/ reason` and `sys.exit(1)`.
 
 A short pairwise table is also printed to stderr at the end of a run.
 
 ## Dependencies
 
 ```
 pip install requests pyyaml
 ```
 
 ## Notes
 
 - The script does not parallelize requests against a single server.
   quickLift renders are single-threaded per request; parallel requests would
   measure contention rather than work.
 - If hgTracks returns the bot-block page or an `errAbort`, the row is
   written with `error` set and `*_ms` empty rather than aborting the run.
 - `total_ms` is the wall time inside hgTracks for the full request (cart
   load + track load + track draw + page assembly). `http_ms` adds network
   and CGI startup; treat it as a sanity check, not as the headline number.
 - Each request reloads the saved session into a fresh cart, so the
   per-request work includes session unmarshaling. That is consistent
   across variants, so it cancels out in the ratio.
 - For paper-quality numbers, run repeatedly across hours of the day or
   pin to a quiet host; render times on a shared dev server have noticeable
   load-dependent jitter.