Codex/splayed clickbench#212
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The fused top-count path (use_emit_filter, n_keys>1) open-addresses
into one monolithic table sized to the row count. For a 10M-row
composite group-by — q32 `by {WatchID, ClientIP}` — that table is
~16M slots across three arrays (~290 MB); every probe is a cache
miss and the loop runs at memory latency.
group.c already has a radix-partitioned group path (radix_phase1/2/3)
that partitions rows into cache-sized chunks and groups each locally.
Gate the monolithic path to cap <= 2^19 slots; above that, bail via
the existing `goto skip_top_count_filter` to the radix path.
ClickBench 10M splayed: q32 1020->247ms, q18 1293->418ms,
q16 567->246ms. 2407/2408 tests pass.
Two algorithmic fixes to exec_group: 1. strlen-on-SYM aggregates (avg/sum(strlen(sym_col))) resolved the symbol per row via ray_sym_str — a spin-lock + dict lookup each call. ClickBench q27 `avg(strlen URL)` over 10M rows spent 91% of its time in ray_sym_str/sym_lock. Borrow the sym→string snapshot once before the da_accum dispatch and index it lock-free in both da_accum_row paths (all-SUM fast path and the general path). q27: 1111 ms -> ~100 ms. 2. The single-key sparse_i64 top-count path open-addresses into a monolithic table that rehashes up to ~16M entries for a high-cardinality key (q15 `by UserID`), cache-thrashing. Above 2^21 rows, bail to the radix-partitioned path. q15: 357 -> 230 ms. 2407/2408 tests pass.
…oup-by
The radix dispatch was gated `!rowsel`, so any composite group-by with
a WHERE clause fell back to the monolithic hash — scanning all 10M
rows into a row-count-sized table. q31 (`by {WatchID,ClientIP}` with
`where SearchPhrase<>''`) ran 650 ms despite the filter cutting the
input ~20x.
radix_phase1_fn already honours c->rowsel (skips non-passing rows
during the scatter), so the partitioned data only ever holds passing
rows — the gate was over-conservative. Dropping it routes filtered
composite group-bys onto the cache-friendly radix path.
q31: 650 -> 175 ms. 2407/2408 tests pass.
…osite group-by" This reverts commit 03004e9.
…ix path" This reverts commit 22edfd4.
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