src/Sstable.bend

mylsm-lsm-store@0.6.0.1 · 536 lines · 67 definitions

1import Base
2import mylsm-lsm-store@0.6.0.1/src/Keys.bend as Keys
3import mylsm-lsm-store@0.6.0.1/src/MemTable.bend as MemTable
4import mylsm-lsm-store@0.6.0.1/src/BitTree.bend as BitTree
5import mylsm-lsm-store@0.6.0.1/src/SortedRun.bend as SortedRun
6
7# SSTables (Task 4): immutable strict sorted runs with BitTree Bloom filters.
8# `build` canonicalizes newest-first raw entries; `from_sorted_unique` trusts an
9# already strict, unique run and deliberately performs no sorting.
10
11# Represent Bloom data used by the SSTable indexes, filters, and lookup.
12type Bloom is Data:
13  Blm{bits: BitTree.BitTree, size: Nat}
14
15# Represent Table data used by the SSTable indexes, filters, and lookup.
16type Table is Data:
17  Tbl{
18    entries: List<&2, MemTable.Entry>,
19    filter: Bloom,
20    nbits: Nat,
21    smallest: Maybe<&2, String>,
22    largest: Maybe<&2, String>,
23    count: Nat,
24    chunks: List<&2, List<&2, MemTable.Entry>>,
25    blocks: List<&2, String>
26  }
27
28# Handle the block entries for the SSTable indexes, filters, and lookup.
29def block_entries() -> Nat:
30  64n
31
32# Handle the chunk go for the SSTable indexes, filters, and lookup.
33def chunk_go(
34  fuel: Nat,
35  +entries: List<&2, MemTable.Entry>,
36  +cur: List<&2, MemTable.Entry>,
37  room: Nat,
38  acc: List<&2, List<&2, MemTable.Entry>>
39) -> List<&2, List<&2, MemTable.Entry>>:
40  match fuel:
41    case 0n:
42      List.reverse(&2, List<&2, MemTable.Entry>, Con{List.reverse(&2, MemTable.Entry, cur), acc})
43    case 1n+f:
44      match entries:
45        case Nil{}:
46          List.reverse(&2, List<&2, MemTable.Entry>, Con{List.reverse(&2, MemTable.Entry, cur), acc})
47        case Con{e, t}:
48          match room:
49            case 0n:
50              chunk_go(f, t, Con{e, Nil{}}, Nat.sub(block_entries(), 1n), Con{List.reverse(&2, MemTable.Entry, cur), acc})
51            case 1n+r:
52              chunk_go(f, t, Con{e, cur}, r, acc)
53
54# Handle chunk in the SSTable indexes, filters, and lookup.
55def chunk(+entries: List<&2, MemTable.Entry>) -> List<&2, List<&2, MemTable.Entry>>:
56  match entries:
57    case Nil{}:
58      Nil{}
59    case Con{e, t}:
60      chunk_go(List.length(&2, MemTable.Entry, entries), t, Con{e, Nil{}}, Nat.sub(block_entries(), 1n), Nil{})
61
62# Handle the chunk head key for the SSTable indexes, filters, and lookup.
63def chunk_head_key(+xs: List<&2, MemTable.Entry>) -> Maybe<&2, String>:
64  match xs:
65    case Nil{}:
66      None{}
67    case Con{MemTable.Entry{key, val}, t}:
68      Some{key}
69
70# Handle the block cons acc for the SSTable indexes, filters, and lookup.
71def block_cons_acc(head: Maybe<&2, String>, acc: List<&2, String>) -> List<&2, String>:
72  match head:
73    case None{}:
74      acc
75    case Some{k}:
76      Con{k, acc}
77
78# Handle the block keys for the SSTable indexes, filters, and lookup.
79def block_keys(+chunks: List<&2, List<&2, MemTable.Entry>>, acc: List<&2, String>) -> List<&2, String>:
80  match chunks:
81    case Nil{}:
82      List.reverse(&2, String, acc)
83    case Con{c, t}:
84      block_keys(t, block_cons_acc(chunk_head_key(c), acc))
85
86# Represent Metadata data used by the SSTable indexes, filters, and lookup.
87type Metadata is Data:
88  Meta{smallest: Maybe<&2, String>, largest: Maybe<&2, String>, count: Nat}
89
90# --- Bloom allocator (Monkey-style: smaller/upper levels get more bits) ---
91# Closed form pinned here; Dayan-exact coefficients are tuning follow-up.
92def bloom_bits(level: Nat, est_keys: Nat) -> Nat:
93  match level:
94    case 0n:
95      Nat.mul(est_keys, 20n)
96    case 1n+m:
97      match m:
98        case 0n:
99          Nat.mul(est_keys, 10n)
100        case 1n+p:
101          Nat.mul(est_keys, 5n)
102
103# --- Local byte hash (kept stable for on-disk/rebuild compatibility) ---
104def bhash(str: String, acc: U32) -> U32:
105  match str:
106    case SNil{}:
107      acc
108    case SCon{c, t}:
109      bhash(t, U32.add(U32.mul(acc, 31), Char.to_u32(c)))
110
111# --- U32->Nat bridges that stay checker-tractable ---
112# The Bend checker does not share across sequentially-chained U32.mul terms:
113# `U32.to_nat` applied to a hash accumulated over 4+ bytes diverges in
114# `{==}` elaboration (runtime is unaffected). The bridges below therefore
115# never materialize a chained U32 as a Nat: each `to_nat` covers at most two
116# U32 ops (shift+mask on the ORIGINAL word — parallel, shared), and all
117# accumulation happens in small-Nat land. Both are EXACT (no semantic
118# change): bytes are the base-256 digits of the word (Horner), so
119# u32_to_nat_exact(w) == U32.to_nat(w) and bhash_n computes the same mod.
120def u32_byte(+word: U32, shift: Nat) -> Nat:
121  U32.to_nat(U32.and(U32.shrn(word, shift), 255))
122
123# Encode or decode a 32-bit word for to nat exact for the SSTable indexes, filters, and lookup.
124def u32_to_nat_exact(+word: U32) -> Nat:
125  +b0 = u32_byte(word, 24n)
126  +b1 = u32_byte(word, 16n)
127  +b2 = u32_byte(word, 8n)
128  +b3 = u32_byte(word, 0n)
129  Nat.add(Nat.mul(b0, Nat.mul(Nat.mul(256n, 256n), 256n)), Nat.add(Nat.mul(b1, Nat.mul(256n, 256n)), Nat.add(Nat.mul(b2, 256n), b3)))
130
131# Handle bhash n pos in the SSTable indexes, filters, and lookup.
132def bhash_n_pos(+str: String, +seed: U32, +mod: Nat) -> Nat:
133  +w = bhash(str, seed)
134  +a0 = Nat.mod(u32_byte(w, 24n), mod)
135  +a1 = Nat.mod(Nat.add(Nat.mul(a0, 256n), u32_byte(w, 16n)), mod)
136  +a2 = Nat.mod(Nat.add(Nat.mul(a1, 256n), u32_byte(w, 8n)), mod)
137  Nat.mod(Nat.add(Nat.mul(a2, 256n), u32_byte(w, 0n)), mod)
138
139# Handle bhash n in the SSTable indexes, filters, and lookup.
140def bhash_n(str: String, seed: U32, mod: Nat) -> Nat:
141  match mod:
142    case 0n:
143      0n
144    case 1n+p:
145      bhash_n_pos(str, seed, mod)
146
147# BitTree stores whole U32 words while Bloom.size preserves the exact logical
148# bit count selected by bloom_bits.
149def bit_words(num: Nat) -> Nat:
150  match num:
151    case 0n:
152      0n
153    case 1n+m:
154      Nat.add(1n, Nat.div(m, 32n))
155
156# Handle bit data for new for the SSTable indexes, filters, and lookup.
157def bits_new(+num: Nat) -> BitTree.BitTree:
158  BitTree.new(bit_words(num))
159
160# Handle bit set in the SSTable indexes, filters, and lookup.
161def bit_set(idx: Nat, bits: BitTree.BitTree) -> BitTree.BitTree:
162  BitTree.set(bits, idx)
163
164# Handle bit get in the SSTable indexes, filters, and lookup.
165def bit_get(idx: Nat, bits: BitTree.BitTree) -> Bool:
166  BitTree.test(bits, idx)
167
168# Handle Bloom filter data for new for the SSTable indexes, filters, and lookup.
169def bloom_new(+num: Nat) -> Bloom:
170  Blm{bits_new(num), num}
171
172# Handle Bloom filter data for well formed for the SSTable indexes, filters, and lookup.
173def bloom_well_formed(bloom: Bloom) -> Bool:
174  match bloom:
175    case Blm{+bits, +size}:
176      Bool.and(
177        BitTree.well_formed(bits),
178        Bool.and(
179          Nat.is_eq(BitTree.word_count(bits), bit_words(size)),
180          Nat.is_le(size, BitTree.bit_count(bits))))
181
182# Handle Bloom filter data for add for the SSTable indexes, filters, and lookup.
183def bloom_add(bloom: Bloom, +key: String) -> Bloom:
184  match bloom:
185    case Blm{bits, +size}:
186      Blm{bit_set(bhash_n(key, 17, size), bit_set(bhash_n(key, 257, size), bits)), size}
187
188# Handle both in the SSTable indexes, filters, and lookup.
189def both(lhs: Bool, rhs: Bool) -> Bool:
190  match lhs:
191    case True{}:
192      rhs
193    case False{}:
194      False{}
195
196# Handle Bloom filter data for test for the SSTable indexes, filters, and lookup.
197def bloom_test(bloom: Bloom, +key: String) -> Bool:
198  match bloom:
199    case Blm{+bits, +size}:
200      both(bit_get(bhash_n(key, 17, size), bits), bit_get(bhash_n(key, 257, size), bits))
201
202# Return the table bits for the SSTable indexes, filters, and lookup.
203def table_bits(tab: Table) -> Nat:
204  match tab:
205    case Tbl{entries, filter, nbits, smallest, largest, count, chunks, blocks}:
206      nbits
207
208# Handle the optional value for present for the SSTable indexes, filters, and lookup.
209def maybe_present(tab: Table, +key: String) -> Bool:
210  match tab:
211    case Tbl{entries, filter, nbits, smallest, largest, count, chunks, blocks}:
212      bloom_test(filter, key)
213
214# --- Parallel probe counters (Task 1): sequential leaf, two-way fork, `!` gate ---
215# Single probe as 0/1 for counting.
216def probe_hit_if(present: Bool) -> Nat:
217  match present:
218    case True{}:
219      1n
220    case False{}:
221      0n
222
223# Count matching probes sequentially.
224def probe_hit(+tab: Table, +key: String) -> Nat:
225  probe_hit_if(maybe_present(tab, key))
226
227# Sequential probe count over a probe list.
228def probe_count_seq(+probes: List<&2, String>, +tab: Table) -> Nat:
229  match probes:
230    case Nil{}:
231      0n
232    case Con{+q, t}:
233      Nat.add(probe_count_seq(t, tab), probe_hit(tab, q))
234
235# Two-way parallel probe count; halves share no state.
236def probe_count_par(+probes: List<&2, String>, +tab: Table) -> Nat:
237  +half = Nat.div(List.length(&2, String, probes), 2n)
238  left right = probe_count_seq(List.take(&2, String, probes, half), tab) probe_count_seq(List.drop(&2, String, probes, half), tab)
239  Nat.add(left, right)
240
241# --- Canonicalization and construction ---
242def bloom_of(entries: List<&2, MemTable.Entry>, +blm: Bloom) -> Bloom:
243  match entries:
244    case Nil{}:
245      blm
246    case Con{e, t}:
247      match e:
248        case MemTable.Entry{key, val}:
249          bloom_of(t, bloom_add(blm, key))
250
251# Handle Bloom filter data for union trees for the SSTable indexes, filters, and lookup.
252def bloom_union_trees(+abits: BitTree.BitTree, +bbits: BitTree.BitTree, size: Nat) -> Bloom:
253  match abits:
254    case BitTree.BT{aroot, awords, acap, aheight}:
255      match bbits:
256        case BitTree.BT{broot, bwords, bcap, bheight}:
257          Blm{BitTree.BT{BitTree.union_bits(aroot, broot), awords, acap, aheight}, size}
258
259# Handle Bloom filter data for union for the SSTable indexes, filters, and lookup.
260def bloom_union(ba: Bloom, bb: Bloom) -> Bloom:
261  match ba:
262    case Blm{abits, asize}:
263      match bb:
264        case Blm{bbits, bsize}:
265          bloom_union_trees(abits, bbits, Nat.max(asize, bsize))
266
267# Handle Bloom filter data for of chunk for the SSTable indexes, filters, and lookup.
268def bloom_of_chunk(+chunk: List<&2, MemTable.Entry>, +nb: Nat) -> Bloom:
269  bloom_of(chunk, bloom_new(nb))
270
271# Two-half parallel build (spike 1): one spawn, one union. Sequential below.
272def bloom_of_par(+entries: List<&2, MemTable.Entry>, +nb: Nat) -> Bloom:
273  +half = Nat.div(List.length(&2, MemTable.Entry, entries), 2n)
274  left right = bloom_of_chunk(List.take(&2, MemTable.Entry, entries, half), nb) bloom_of_chunk(List.drop(&2, MemTable.Entry, entries, half), nb)
275  bloom_union(left, right)
276
277# --- Four-chunk parallel build (Task 2): two-level fork, three unions ---
278# Third chunk slice as take-after-drop.
279def chunk_third(+entries: List<&2, MemTable.Entry>, +skip: Nat, +take: Nat) -> List<&2, MemTable.Entry>:
280  List.take(&2, MemTable.Entry, List.drop(&2, MemTable.Entry, entries, skip), take)
281
282# Four-way chunk build with a two-level fork tree.
283def bloom_of_chunks(+entries: List<&2, MemTable.Entry>, +nb: Nat) -> Bloom:
284  +num = List.length(&2, MemTable.Entry, entries)
285  +q = Nat.div(num, 4n)
286  a b = bloom_of_chunk(List.take(&2, MemTable.Entry, entries, q), nb) bloom_of_chunk(chunk_third(entries, q, q), nb)
287  c d = bloom_of_chunk(chunk_third(entries, Nat.mul(q, 2n), q), nb) bloom_of_chunk(List.drop(&2, MemTable.Entry, entries, Nat.mul(q, 3n)), nb)
288  bloom_union(bloom_union(a, b), bloom_union(c, d))
289
290# --- Hybrid bloom (spike): parallel index collection, sequential assembly ---
291# Phase 1 emits a flat index list (two per key); joins concatenate, so no
292# chunk tree or union is ever built. Phase 2 folds the indexes into ONE tree
293# on the CPU. This removes the tree-allocation amplification that costs ~10%
294# at 1M scale in the chunk+union design, while keeping a fork tree that a
295# future `!` can ship once the GPU recovery crash is fixed upstream.
296# Both bit positions of one key as a flat two-element list.
297def key_idxs(+key: String, +size: Nat) -> List<&2, Nat>:
298  Con{bhash_n(key, 17, size), Con{bhash_n(key, 257, size), Nil{}}}
299
300# Sequential index collection over entries.
301def hash_idxs_seq(+entries: List<&2, MemTable.Entry>, +size: Nat) -> List<&2, Nat>:
302  match entries:
303    case Nil{}:
304      Nil{}
305    case Con{MemTable.Entry{key, val}, t}:
306      List.append(&2, Nat, key_idxs(key, size), hash_idxs_seq(t, size))
307
308# Balanced parallel index collection; reusable fuel bounds the fork depth.
309def hash_idxs_par_go(+fuel: Nat, +entries: List<&2, MemTable.Entry>, +size: Nat) -> List<&2, Nat>:
310  match fuel:
311    case 0n:
312      hash_idxs_seq(entries, size)
313    case 1n+f:
314      match entries:
315        case Nil{}:
316          Nil{}
317        case Con{MemTable.Entry{key, val}, Nil{}}:
318          key_idxs(key, size)
319        case Con{_, Con{_, _}}:
320          +half = Nat.div(List.length(&2, MemTable.Entry, entries), 2n)
321          left right = hash_idxs_par_go(f, List.take(&2, MemTable.Entry, entries, half), size) hash_idxs_par_go(f, List.drop(&2, MemTable.Entry, entries, half), size)
322          List.append(&2, Nat, left, right)
323
324# Parallel entry point; fuel covers the fork depth.
325def hash_idxs_par(+entries: List<&2, MemTable.Entry>, +size: Nat) -> List<&2, Nat>:
326  +fuel = List.length(&2, MemTable.Entry, entries)
327  hash_idxs_par_go(fuel, entries, size)
328
329# Sequential assembly of one filter from a flat index list.
330def bloom_set_all(+idxs: List<&2, Nat>, +blm: Bloom) -> Bloom:
331  match idxs:
332    case Nil{}:
333      blm
334    case Con{+i, t}:
335      match blm:
336        case Blm{bits, +size}:
337          bloom_set_all(t, Blm{bit_set(i, bits), size})
338
339# Hybrid build: parallel hashing, single-tree assembly.
340def bloom_of_hybrid(+entries: List<&2, MemTable.Entry>, +nb: Nat) -> Bloom:
341  bloom_set_all(hash_idxs_par(entries, nb), bloom_new(nb))
342
343# Size-gated entry point: sequential on both sides of the gate.
344# MEASURED VERDICT (2026-09-26, 1M interleaved A/B, Darwin arm64, Bend 2.0.28):
345# sequential median 225105 ms (4442 ops/s) vs 4-chunk 249150 ms (4014 ops/s)
346# vs hybrid 261746 ms — the parallel builds cost ~10% (fork/join plus
347# allocation overhead dominates; invisible at 100k, compounds over 244
348# flushes). Confirmed under two machine states (all arms shifted +15k ms on
349# the slow day; relative order unchanged). The parallel builds stay as
350# law-covered spikes; the `!` variants stay opt-in behind the GPU recovery
351# crash documented below.
352def bloom_pick(small: Bool, +entries: List<&2, MemTable.Entry>, +nb: Nat) -> Bloom:
353  match small:
354    case True{}:
355      bloom_of(entries, bloom_new(nb))
356    case False{}:
357      bloom_of(entries, bloom_new(nb))
358
359# Handle Bloom filter data for of auto for the SSTable indexes, filters, and lookup.
360def bloom_of_auto(+entries: List<&2, MemTable.Entry>, +nb: Nat) -> Bloom:
361  bloom_pick(Nat.is_lt(List.length(&2, MemTable.Entry, entries), 2048n), entries, nb)
362
363# Build table metadata for tail for the SSTable indexes, filters, and lookup.
364def metadata_tail(entries: List<&2, MemTable.Entry>, +first: String, last: String, +count: Nat) -> Metadata:
365  match entries:
366    case Nil{}:
367      Meta{Some{first}, Some{last}, count}
368    case Con{MemTable.Entry{key, val}, rest}:
369      metadata_tail(rest, first, key, Nat.add(count, 1n))
370
371# Handle metadata in the SSTable indexes, filters, and lookup.
372def metadata(entries: List<&2, MemTable.Entry>) -> Metadata:
373  match entries:
374    case Nil{}:
375      Meta{None{}, None{}, 0n}
376    case Con{MemTable.Entry{+key, val}, rest}:
377      metadata_tail(rest, key, key, 1n)
378
379# Handle from sorted unique est meta in the SSTable indexes, filters, and lookup.
380def from_sorted_unique_est_meta(+entries: List<&2, MemTable.Entry>, level: Nat, est_keys: Nat, meta: Metadata) -> Table:
381  match meta:
382    case Meta{smallest, largest, count}:
383      +nb = bloom_bits(level, est_keys)
384      Tbl{entries, bloom_of_auto(entries, nb), nb, smallest, largest, count, chunk(entries), block_keys(chunk(entries), Nil{})}
385
386# Handle from sorted unique meta in the SSTable indexes, filters, and lookup.
387def from_sorted_unique_meta(+entries: List<&2, MemTable.Entry>, level: Nat, meta: Metadata) -> Table:
388  match meta:
389    case Meta{smallest, largest, +count}:
390      +nb = bloom_bits(level, count)
391      Tbl{entries, bloom_of_auto(entries, nb), nb, smallest, largest, count, chunk(entries), block_keys(chunk(entries), Nil{})}
392
393# Handle from sorted unique in the SSTable indexes, filters, and lookup.
394def from_sorted_unique(+entries: List<&2, MemTable.Entry>, level: Nat) -> Table:
395  from_sorted_unique_meta(entries, level, metadata(entries))
396
397# Build sorted for the SSTable indexes, filters, and lookup.
398def build_sorted(+entries: List<&2, MemTable.Entry>, level: Nat, est_keys: Nat) -> Table:
399  from_sorted_unique_est_meta(entries, level, est_keys, metadata(entries))
400
401# Handle build in the SSTable indexes, filters, and lookup.
402def build(+entries: List<&2, MemTable.Entry>, level: Nat, est_keys: Nat) -> Table:
403  +effective = Nat.max(est_keys, List.length(&2, MemTable.Entry, entries))
404  build_sorted(SortedRun.sort_newest(entries), level, effective)
405
406# Metadata accessors keep clients independent of the Tbl field layout.
407def table_smallest(tab: Table) -> Maybe<&2, String>:
408  match tab:
409    case Tbl{entries, filter, nbits, smallest, largest, count, chunks, blocks}:
410      smallest
411
412# Return the table largest for the SSTable indexes, filters, and lookup.
413def table_largest(tab: Table) -> Maybe<&2, String>:
414  match tab:
415    case Tbl{entries, filter, nbits, smallest, largest, count, chunks, blocks}:
416      largest
417
418# Return the table count for the SSTable indexes, filters, and lookup.
419def table_count(tab: Table) -> Nat:
420  match tab:
421    case Tbl{entries, filter, nbits, smallest, largest, count, chunks, blocks}:
422      count
423
424# Open bridge: metadata is matched explicitly so the Bloom schedule projects
425# through `build` without relying on reduction of an open entry list.
426def table_bits_from_meta(
427  +entries: List<&2, MemTable.Entry>,
428  level: Nat,
429  est_keys: Nat,
430  meta: Metadata,
431) -> {table_bits(from_sorted_unique_est_meta(entries, level, est_keys, meta)) == bloom_bits(level, est_keys) : Nat}:
432  match meta:
433    case Meta{smallest, largest, count}:
434      {==}
435
436# Return the table bits build for the SSTable indexes, filters, and lookup.
437def table_bits_build(
438  +entries: List<&2, MemTable.Entry>,
439  level: Nat,
440  est_keys: Nat,
441) -> {table_bits(build(entries, level, est_keys)) == bloom_bits(level, Nat.max(est_keys, List.length(&2, MemTable.Entry, entries))) : Nat}:
442  +effective = Nat.max(est_keys, List.length(&2, MemTable.Entry, entries))
443  table_bits_from_meta(SortedRun.sort_newest(entries), level, effective, metadata(SortedRun.sort_newest(entries)))
444
445
446# Block-scoped lookup. Checker constraints (proven by scratch experiments):
447# multi-scrutinee matches follow declaration order, and only Nat answers flow
448# through match arms — so selection returns an index, picked up by chunk_at_go.
449def pick_ix(bt: List<&2, String>, ct: List<&2, List<&2, MemTable.Entry>>, ix: Nat, +key: String, order: Cmp) -> Nat:
450  match bt ct order:
451    case _ _ GT{}:
452      Nat.sub(ix, 1n)
453    case Nil{} _ _:
454      ix
455    case _ Nil{} _:
456      ix
457    case Con{b2, bt2} Con{d2, ct2} LT{}:
458      pick_ix(bt2, ct2, Nat.add(ix, 1n), key, Keys.cmp(b2, key))
459    case Con{b2, bt2} Con{d2, ct2} EQ{}:
460      ix
461
462# Handle the chunk at go for the SSTable indexes, filters, and lookup.
463def chunk_at_go(fuel: Nat, +chunks: List<&2, List<&2, MemTable.Entry>>, ix: Nat) -> List<&2, MemTable.Entry>:
464  match fuel chunks:
465    case 0n _:
466      Nil{}
467    case 1n+f Nil{}:
468      Nil{}
469    case 1n+f Con{c, t}:
470      match ix:
471        case 0n:
472          c
473        case 1n+p:
474          chunk_at_go(f, t, p)
475
476# Handle the chunk at for the SSTable indexes, filters, and lookup.
477def chunk_at(+chunks: List<&2, List<&2, MemTable.Entry>>, ix: Nat) -> List<&2, MemTable.Entry>:
478  chunk_at_go(List.length(&2, List<&2, MemTable.Entry>, chunks), chunks, ix)
479
480# Handle the block scan for the SSTable indexes, filters, and lookup.
481def block_scan(+chunk: List<&2, MemTable.Entry>, +key: String) -> Maybe<&2, String>:
482  MemTable.get(MemTable.MT{chunk}, key)
483
484# Handle the block pick for the SSTable indexes, filters, and lookup.
485def block_pick(
486  +chunks: List<&2, List<&2, MemTable.Entry>>,
487  +blocks: List<&2, String>,
488  +key: String
489) -> List<&2, MemTable.Entry>:
490  match chunks blocks:
491    case Nil{} _:
492      Nil{}
493    case _ Nil{}:
494      Nil{}
495    case Con{c, ct} Con{b, bt}:
496      chunk_at(chunks, pick_ix(bt, ct, 0n, key, Keys.cmp(b, key)))
497
498# Handle the block finish for the SSTable indexes, filters, and lookup.
499def block_finish(
500  picked: List<&2, MemTable.Entry>,
501  +entries: List<&2, MemTable.Entry>,
502  +key: String
503) -> Maybe<&2, String>:
504  match picked:
505    case Nil{}:
506      MemTable.get(MemTable.MT{entries}, key)
507    case Con{e, t}:
508      block_scan(Con{e, t}, key)
509
510# Resolve the hit for finish for the SSTable indexes, filters, and lookup.
511def hit_finish(
512  picked: List<&2, MemTable.Entry>,
513  +entries: List<&2, MemTable.Entry>,
514  +key: String
515) -> Maybe<&2, Maybe<&2, String>>:
516  match picked:
517    case Nil{}:
518      MemTable.get_hit(MemTable.MT{entries}, key)
519    case Con{e, t}:
520      MemTable.get_hit(MemTable.MT{Con{e, t}}, key)
521
522# Handle the block get hit for the SSTable indexes, filters, and lookup.
523def block_get_hit(tab: Table, +key: String) -> Maybe<&2, Maybe<&2, String>>:
524  match tab:
525    case Tbl{entries, filter, nbits, smallest, largest, count, chunks, blocks}:
526      hit_finish(block_pick(chunks, blocks, key), entries, key)
527
528# Handle the block get for the SSTable indexes, filters, and lookup.
529def block_get(tab: Table, +key: String) -> Maybe<&2, String>:
530  match tab:
531    case Tbl{entries, filter, nbits, smallest, largest, count, chunks, blocks}:
532      block_finish(block_pick(chunks, blocks, key), entries, key)
533
534# Handle lookup in the SSTable indexes, filters, and lookup.
535def lookup(tab: Table, +key: String) -> Maybe<&2, String>:
536  block_get(tab, key)