Ryan Malloy
347acf0906
Two bugs in gist_tle.c caused the && (overlap) operator to return zero results through the GiST index while sequential scan worked: 1. gist_tle_union read from vector[FirstOffsetNumber] (index 1), skipping vector[0] which holds the accumulated union key. Every internal node collapsed to a single-entry bounding box. Fixed: seed from vector[0], loop from 1. 2. All GiST key allocations used sizeof(tle_orbital_key) (32 bytes) or sizeof(pg_tle) (104 bytes), but INTERNALLENGTH is 112. index_form_tuple() copies typlen bytes, causing buffer overread. Fixed: TLE_TYPLEN constant (112) for all index datum allocations. The <-> (KNN distance) operator was unaffected because it uses gist_tle_distance, not gist_tle_consistent. Verified against 66,440-object catalog: - && consistency: 9 seqscan == 9 GiST (ISS conjunction) - <-> KNN: 10 nearest in 2.1ms via index-ordered scan - All 15 regression tests pass
169 lines
8.8 KiB
Plaintext
169 lines
8.8 KiB
Plaintext
pg_orrery Full Index Benchmark — 66k Catalog
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===========================================================
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Date: 2026-02-18
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PostgreSQL: 18.1
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Catalog: 66,440 objects (merged from 4 sources)
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Sources: Space-Track (66,248), CelesTrak active (5 unique),
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SatNOGS (110 unique), CelesTrak SupGP (77 unique + 8,167 epoch updates)
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Includes: 362 Alpha-5 objects (NORAD > 99,999)
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Orbital regime breakdown:
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LEO (<2000km): 63,097 (95.0%)
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GEO/HEO (>34000km): 1,760 ( 2.6%)
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MEO (2000-20000km): 1,277 ( 1.9%)
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GEO-transfer: 306 ( 0.5%)
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Index sizes:
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SP-GiST (tle_spgist_ops): 67 ms build, 11 MB
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GiST (tle_ops): 93 ms build, 15 MB
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═══════════════════════════════════════════════════════════
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SP-GiST: Visibility Cone (&?) — "Can this satellite pass over me?"
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═══════════════════════════════════════════════════════════
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SP-GiST prunes by altitude band, inclination, and RAAN window.
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The &? operator answers: "Could this satellite be visible from this
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observer during this time window above this minimum elevation?"
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Query │ SP-GiST │ Seqscan │ Candidates │ Pruned%
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───────────────────────┼──────────┼──────────┼────────────┼────────
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Eagle 2h/10deg │ 16.1 ms │ 12.1 ms │ 10,763 │ 83.8%
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Eagle 24h/10deg │ 23.3 ms │ 12.5 ms │ 61,426 │ 7.5%
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Equator 2h/10deg │ 16.8 ms │ 12.1 ms │ 10,174 │ 84.7%
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Eagle 2h/45deg │ 16.9 ms │ 11.9 ms │ 6,796 │ 89.8%
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Consistency: PASS (all 4 scenarios: 0 false neg, 0 false pos)
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═══════════════════════════════════════════════════════════
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GiST: Overlap (&&) — "Does this satellite share my orbit band?"
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═══════════════════════════════════════════════════════════
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GiST groups satellites by [altitude_low, altitude_high] × [inclination].
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The && operator answers: "Do these two TLEs occupy overlapping orbit bands?"
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Used for conjunction screening — finding potential collision partners.
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Critical bugfix in this session:
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Bug 1: palloc size mismatch (sizeof(pg_tle)=104 vs INTERNALLENGTH=112)
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Bug 2: gist_tle_union used 1-based indexing (picksplit convention)
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instead of 0-based (union convention), skipping vector[0]
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Query │ GiST │ Seqscan │ Matches
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───────────────────────┼──────────┼──────────┼────────
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ISS conjunction │ 10.9 ms │ 63.3 ms │ 9
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Starlink-230369 │ 9.5 ms │ 14.9 ms │ 0
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SYNCOM 2 (GEO) │ 4.0 ms │ 7.2 ms │ 0
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Consistency: PASS (ISS: 9 seqscan == 9 GiST, 0 mismatch)
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ISS conjunction candidates (altitude + inclination overlap):
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PROGRESS MS-31, PROGRESS MS-32, SOYUZ MS-28,
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DRAGON FREEDOM 3, DRAGON CRS-33, CYGNUS NG-23,
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HTV-X1, ISS (NAUKA), OBJECT E
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— All ISS-visiting vehicles or co-orbital modules. ✓
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═══════════════════════════════════════════════════════════
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GiST: KNN (<->) — "What's nearest to this orbit?"
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═══════════════════════════════════════════════════════════
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GiST KNN uses altitude-band distance for index-ordered scans.
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The <-> operator returns orbital altitude separation in km.
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Probe must be a scalar subquery for index ordering to activate.
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Query │ GiST KNN │ Buffers │ Notes
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───────────────────────┼──────────┼─────────┼──────────────
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10 nearest to ISS │ 2.1 ms │ 982 │ Index-ordered
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10 nearest to SYNCOM 2 │ 0.2 ms │ 40 │ Index-ordered
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100 nearest to ISS │ 1.4 ms │ 1,062 │ Index-ordered
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Within 50km of ISS │ 16.0 ms │ 4,014 │ 12,496 matches
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Pattern for KNN queries (probe as scalar subquery):
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ORDER BY b.tle <-> (SELECT tle FROM catalog WHERE norad_id = 25544 LIMIT 1)
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LIMIT 10;
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→ Index Scan using bench_gist_idx, Order By: tle <-> InitPlan
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═══════════════════════════════════════════════════════════
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EXPLAIN ANALYZE Details
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═══════════════════════════════════════════════════════════
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SP-GiST 2h/Eagle/10deg:
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Index Only Scan using bench_spgist_idx
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Heap Fetches: 0 (pure index scan)
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Buffers: shared hit=4964
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17.5 ms execution
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SeqScan 2h/Eagle/10deg:
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Seq Scan, Filter rows removed: 55,677
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Buffers: shared hit=1338
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12.5 ms execution
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GiST && ISS conjunction:
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Nested Loop → Index Scan using bench_gist_idx
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Index Cond: (tle && a.tle)
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Index Searches: 1, Buffers: shared hit=287
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4.1 ms execution
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GiST KNN 10 nearest ISS:
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Index Scan using bench_gist_idx
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Order By: (tle <-> InitPlan)
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Index Searches: 1
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2.1 ms execution
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═══════════════════════════════════════════════════════════
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Pruning Summary
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═══════════════════════════════════════════════════════════
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Scenario │ Catalog │ Candidates │ Candidate% │ Pruned%
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─────────────────┼─────────┼────────────┼────────────┼────────
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2h/Eagle/10deg │ 66,440 │ 10,763 │ 16.2% │ 83.8%
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2h/Equator/10deg │ 66,440 │ 10,174 │ 15.3% │ 84.7%
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2h/Eagle/45deg │ 66,440 │ 6,796 │ 10.2% │ 89.8%
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24h/Eagle/10deg │ 66,440 │ 61,426 │ 92.5% │ 7.5%
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═══════════════════════════════════════════════════════════
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Application Queries
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═══════════════════════════════════════════════════════════
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"What's overhead right now?" (SP-GiST filter + SGP4 propagation):
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15 satellites above horizon, top: NAVSTAR 57 at 81.7° el
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107 ms (includes SGP4 propagation for each candidate)
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ISS pass prediction (next 24h from 66k catalog):
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6 passes found, max 87.6° elevation
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3.8 ms
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ISS conjunction screening (GiST && on 66k catalog):
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9 co-orbital objects found
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4.6 ms via GiST (vs 63.3 ms seqscan — 5.8x speedup)
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═══════════════════════════════════════════════════════════
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Key Observations
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═══════════════════════════════════════════════════════════
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1. GiST && is the clear winner for conjunction screening:
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- ISS: 10.9ms GiST vs 63.3ms seqscan (5.8x speedup)
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- Only 287 buffer hits vs 1,338 for seqscan
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- Returns exactly the right 9 co-orbital objects
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2. GiST KNN is extremely fast for "nearest orbit" queries:
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- 10 nearest: 2.1ms with index ordering
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- GEO satellite: 0.15ms (sparse regime, fewer nodes to traverse)
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- Requires scalar subquery probe pattern for index ordering
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3. SP-GiST visibility cone handles 2h windows well:
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- 83.8% pruning at 10° min_el (Eagle, 2h)
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- 89.8% pruning at 45° min_el
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- Falls behind seqscan at 24h windows (7.5% pruning not worth index overhead)
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4. Both indexes are compact:
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- SP-GiST: 11 MB for 66k objects (170 bytes/object)
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- GiST: 15 MB for 66k objects (237 bytes/object)
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- Build times: 67ms and 93ms respectively
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5. Zero false positives/negatives across all consistency checks.
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Alpha-5 support:
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- Bill Gray's get_el.c parser handles Alpha-5 natively
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- T0002 → 270002, A0001 → 100001, Z9999 → 339999 ✓
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- Round-trip (parse → output) preserves Alpha-5 encoding ✓
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- 362 Alpha-5 objects loaded and indexed without issues ✓
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