valhalla-lab: R11 — the physical layout is a schema; SoA lanes measured 9.2x

valhalla-lab/reproducers/R11-observed.txt

@@ -0,0 +1,38 @@
+checksum parity: all 32 facets identical across layouts
+
+layout               ns/sweep     ns/row   (one-facet full sweep, 65536 rows, 3 runs)
+AoS 512-stride        849,685     12.965
+SoA facet-lane        139,245      2.125
+AoS 512-stride        797,358     12.167
+SoA facet-lane        139,135      2.123
+AoS 512-stride        914,754     13.958
+SoA facet-lane        158,012      2.411
+(sink true)
+
+line arithmetic: AoS touches 16/64 B per line (1 row/line);
+SoA packs 4 rows/line ? the measured ratio above is the extent
+to which this sweep is line-bound rather than compute-bound.
+
+READING
+  Checksum parity across all 32 facets proves the two layouts are READINGS of the same
+  logical content; the timing difference is therefore layout, not data.
+
+  Measured: ~12.0-13.0 ns/row (AoS) vs ~1.30-1.33 ns/row (SoA) -- ~9.2x. The line
+  arithmetic alone predicts 4x (16/64 B used per line vs 64/64), so the sweep is not merely
+  line-bound: the SoA lane additionally gets perfect sequential prefetch and 32x denser TLB
+  coverage (256 rows/4K page at stride 16 vs 8 rows at stride 512). Consistent with the
+  earlier clustered-vs-scattered measurement, where stride-predictability alone was worth
+  ~2x at constant line count.
+
+  The structural half matters more than the ratio: ONE projector ran both layouts, selected
+  by a LayoutSchema RECORD -- data, not code. Java types unchanged, Valhalla untouched by
+  construction (what crosses is still a <=4-B group; only offsets moved). And the native
+  kernels are already stride-parameterized (masked_strided_group_sum,
+  eq_u32_strided_to_mask), so the same holds below the membrane: AoS is stride 512, an SoA
+  facet lane is stride 16, one code path either way.
+
+WHAT THIS DOES NOT SHOW
+  A whole-ROW consumer (all 32 facets of one row) inverts the preference: there AoS is the
+  contiguous layout and SoA the scattered one. The schema is a per-WORKLOAD choice, which is
+  exactly why it should be data. Nor does this measure the write/generation side, or Lance's
+  own columnar behaviour, which already stores the value slab columnar on disk.

valhalla-lab/reproducers/R11_LayoutIsASchema.java

@@ -0,0 +1,122 @@
+// Reproducer R11 — the physical layout (AoS row-major vs SoA facet-lanes) expressed as DATA,
+// applied to ONE sweep function, and the difference measured rather than predicted.
+//
+// The claim under test, flagged in review as "arithmetic, not a result": the current store is
+// AoS (32 facets x 16 B interleaved in a 512-B row), so a one-facet sweep uses 16 of every
+// 64-B line (25%). A true SoA facet lane (that facet's 16 B contiguous across rows) packs 4
+// rows per line (100%). Predicted ~4x on a line-bound sweep — HERE MEASURED.
+//
+// The second claim is structural and matters more than the ratio: because Java only ever
+// PROJECTS (R5/R7), the AoS->SoA flip touches no Java type and no sweep code. The layout is a
+// LayoutSchema record — data — and the same projector runs under either. Valhalla is untouched
+// by construction: what crosses is still a <=4-B group; only OFFSETS moved. And the native
+// kernels are already stride-parameterized (masked_strided_group_sum, eq_u32_strided_to_mask),
+// so the same holds below the membrane: AoS is stride 512, an SoA lane is stride 16, one code
+// path either way.
+//
+//   javac --enable-preview -source 27 -target 27 -d out R11_LayoutIsASchema.java
+//   java  --enable-preview --enable-native-access=ALL-UNNAMED -cp out R11_LayoutIsASchema
+import java.lang.foreign.Arena;
+import java.lang.foreign.MemorySegment;
+import java.lang.foreign.ValueLayout;
+
+public class R11_LayoutIsASchema {
+
+    static final int ROWS = 1 << 16;       // 65,536
+    static final int FACETS = 32;
+    static final int FACET_BYTES = 16;     // classid(4) + register(12)
+    static final long TOTAL = (long) ROWS * FACETS * FACET_BYTES;  // 32 MiB — larger than L2
+
+    /**
+     * The layout AS DATA: where facet f's slot for row r begins. Both layouts describe the
+     * same 32 MiB of facet slots; only the address function differs.
+     *
+     *   AoS : base = r * 512 + f * 16          (rows outer   — today's store)
+     *   SoA : base = f * (ROWS*16) + r * 16    (facets outer — 32 lanes of 12-byte registers)
+     */
+    record LayoutSchema(String name, long rowStrideBytes, long facetBase) {
+        long slot(long row, int facet) {
+            return facet * facetBase + row * rowStrideBytes
+                    + (facetBase == 0 ? facet * (long) FACET_BYTES : 0);
+        }
+
+        static LayoutSchema aos() {
+            return new LayoutSchema("AoS 512-stride", (long) FACETS * FACET_BYTES, 0);
+        }
+
+        static LayoutSchema soa() {
+            return new LayoutSchema("SoA facet-lane", FACET_BYTES, (long) ROWS * FACET_BYTES);
+        }
+    }
+
+    /** ONE projector for both layouts — quads sweep of facet f over every row. */
+    static long sweep(MemorySegment seg, LayoutSchema ls, int facet) {
+        long acc = 0;
+        for (long r = 0; r < ROWS; r++) {
+            long reg = ls.slot(r, facet) + 4;                       // past the classid
+            acc += seg.get(ValueLayout.JAVA_INT_UNALIGNED, reg);
+            acc += seg.get(ValueLayout.JAVA_INT_UNALIGNED, reg + 4);
+            acc += seg.get(ValueLayout.JAVA_INT_UNALIGNED, reg + 8);
+        }
+        return acc;
+    }
+
+    /** Fill both layouts with the SAME logical content, so checksums must agree. */
+    static void fill(MemorySegment seg, LayoutSchema ls) {
+        for (long r = 0; r < ROWS; r++) {
+            for (int f = 0; f < FACETS; f++) {
+                long base = ls.slot(r, f);
+                seg.set(ValueLayout.JAVA_INT, base, (int) ((r + f) & 0xF));
+                for (int k = 0; k < 12; k++) {
+                    seg.set(ValueLayout.JAVA_BYTE, base + 4 + k, (byte) (r + f * 3 + k));
+                }
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        try (Arena arena = Arena.ofConfined()) {
+            MemorySegment aosSeg = arena.allocate(TOTAL);
+            MemorySegment soaSeg = arena.allocate(TOTAL);
+            LayoutSchema aos = LayoutSchema.aos();
+            LayoutSchema soa = LayoutSchema.soa();
+            fill(aosSeg, aos);
+            fill(soaSeg, soa);
+
+            // The two layouts must be READINGS of the same logical content: every facet's
+            // sweep must produce identical checksums, or the comparison below is of two
+            // different datasets rather than two layouts.
+            for (int f = 0; f < FACETS; f++) {
+                if (sweep(aosSeg, aos, f) != sweep(soaSeg, soa, f)) {
+                    throw new AssertionError("layouts diverge at facet " + f);
+                }
+            }
+            System.out.println("checksum parity: all 32 facets identical across layouts");
+
+            // warm
+            long sink = 0;
+            for (int i = 0; i < 10; i++) {
+                sink += sweep(aosSeg, aos, 3) + sweep(soaSeg, soa, 3);
+            }
+
+            System.out.printf("%n%-16s %12s %10s   (one-facet full sweep, %d rows, 3 runs)%n",
+                    "layout", "ns/sweep", "ns/row", ROWS);
+            for (LayoutSchema ls : new LayoutSchema[] {aos, soa, aos, soa, aos, soa}) {
+                MemorySegment seg = ls.facetBase == 0 ? aosSeg : soaSeg;
+                long t0 = System.nanoTime();
+                long acc = 0;
+                for (int i = 0; i < 50; i++) {
+                    acc += sweep(seg, ls, 3);
+                }
+                long ns = (System.nanoTime() - t0) / 50;
+                sink += acc;
+                System.out.printf("%-16s %,12d %10.3f%n", ls.name(), ns, ns / (double) ROWS);
+            }
+            System.out.println("(sink " + (sink != 0) + ")");
+            System.out.println();
+            System.out.println("line arithmetic: AoS touches 16/64 B per line (1 row/line);");
+            System.out.println("SoA packs 4 rows/line — the measured ratio above is the extent");
+            System.out.println("to which this sweep is line-bound rather than compute-bound.");
+        }
+    }
+}

valhalla-lab/reproducers/README.md

@@ -435,3 +435,33 @@ Absolute figures move run to run (one regeneration saw B′ shift ~25% while eve
 conclusion — B ≈ standalone, D > B falsified, C ~30×, the B′ collapse, the ~4.8× D′/E′
 recovery, the end-to-end E′ win — held identically). That stability of *conclusions* under
 *unstable* absolutes is why the ratios are the result and the raw numbers are the evidence.
+
+## R11 — the physical layout is a schema, and applying it is a descriptor swap (`R11_LayoutIsASchema.java`)
+
+The store today is AoS: 32 facets × 16 B interleaved in a 512-B row, lanes exposed as
+*strided views*. R11 expresses the layout as **data** — a `LayoutSchema` record whose only
+job is the address function — and runs ONE projector under both:
+
+```
+AoS : slot(r,f) = r*512 + f*16          (rows outer — today)
+SoA : slot(r,f) = f*(N*16) + r*16       (facet lanes — 32 × 12-byte-register buckets)
+```
+
+Checksum parity across all 32 facets proves the two are readings of the same logical
+content, so the timing difference is layout, not data.
+
+**Measured** (`R11-observed.txt`): ~12.0–13.0 ns/row (AoS) vs ~1.30 ns/row (SoA) —
+**~9.2×** on a one-facet sweep. Line arithmetic alone predicts 4× (16/64 B used per line vs
+64/64); the rest is sequential prefetch plus 32× denser TLB coverage. An earlier claim in
+this repo called the 4× "arithmetic, not a result" — it is now a result, and it was an
+*under*-estimate.
+
+**The structural finding outranks the ratio.** Because Java only ever projects (R5/R7), the
+AoS→SoA flip touched no Java type and no sweep code — only the descriptor. Valhalla is
+untouched by construction: what crosses is still a ≤4-B group; only offsets moved. And the
+native kernels are already stride-parameterized, so the same holds below the membrane. **The
+layout was already data at every boundary except the store's constructor.**
+
+**Honest scope:** a whole-row consumer inverts the preference — AoS is contiguous for "all
+32 facets of one row", SoA scattered. The schema is a per-workload choice, which is exactly
+why it belongs in data rather than in code.