src/MergeIter.bend
mylsm-lsm-store@0.3.0.0 · 67 lines · 0 definitions
1import Base
2import mylsm-lsm-store@0.3.0.0/src/Keys.bend as Keys
3import mylsm-lsm-store@0.3.0.0/src/MemTable.bend as MemTable
4import mylsm-lsm-store@0.3.0.0/src/Sstable.bend as Sstable
5import mylsm-lsm-store@0.3.0.0/src/SortedRun.bend as SortedRun
6
7# Merge iterator (Task 6): concat sources (memtable newest-first, then
8# SSTables newest-level-first) and canonicalize with balanced stable merge;
9# first-inserted wins ties = newest wins). The range+tombstone filter is
10# pump+fuel+leaf: String.cmp hands both strings back beside the verdict,
11# so the key survives the keep/drop decision with no clone primitive.
12# Order of defs is load-bearing (Bend 2: only backward references).
13
14def scan_put2(pair: (String & String) & Cmp, +val: String, acc: List<&2, MemTable.Entry>) -> List<&2, MemTable.Entry>:
15 match pair:
16 case ((k3, _), c):
17 match c:
18 case LT{}:
19 Con{MemTable.Entry{k3, Some{val}}, acc}
20 case EQ{}:
21 acc
22 case GT{}:
23 acc
24
25def scan_put(pair: (String & String) & Cmp, +hi: String, +val: String, acc: List<&2, MemTable.Entry>) -> List<&2, MemTable.Entry>:
26 match pair:
27 case ((k2, _), c):
28 match c:
29 case LT{}:
30 acc
31 case EQ{}:
32 scan_put2(String.cmp(k2, hi), val, acc)
33 case GT{}:
34 scan_put2(String.cmp(k2, hi), val, acc)
35
36def scan_go(fuel: Nat, +lo: String, +hi: String, acc: List<&2, MemTable.Entry>, xs: List<&2, MemTable.Entry>) -> List<&2, MemTable.Entry>:
37 match fuel:
38 case 0n:
39 List.reverse(&2, MemTable.Entry, acc)
40 case 1n+f:
41 match xs:
42 case Nil{}:
43 List.reverse(&2, MemTable.Entry, acc)
44 case Con{MemTable.Entry{key, val}, t}:
45 match val:
46 case None{}:
47 scan_go(f, lo, hi, acc, t)
48 case Some{v}:
49 scan_go(f, lo, hi, scan_put(String.cmp(key, lo), hi, v, acc), t)
50
51# Newest-first concat: memtable entries, then each level's tables in order.
52def flatten(mem: List<&2, MemTable.Entry>, levels: List<&2, List<&2, MemTable.Entry>>) -> List<&2, MemTable.Entry>:
53 match levels:
54 case Nil{}:
55 mem
56 case Con{h, t}:
57 List.append(&2, MemTable.Entry, mem, List.concat(&2, MemTable.Entry, Con{h, t}))
58
59# Full merge: sorted, unique, newest version wins each key.
60def merge(mem: List<&2, MemTable.Entry>, levels: List<&2, List<&2, MemTable.Entry>>) -> List<&2, MemTable.Entry>:
61 SortedRun.sort_newest(flatten(mem, levels))
62
63# Range scan over a merged run: lo <= key < hi, tombstones dropped.
64def scan(+merged: List<&2, MemTable.Entry>, lo: String, hi: String) -> List<&2, MemTable.Entry>:
65 scan_go(List.length(&2, MemTable.Entry, merged), lo, hi, Nil{}, merged)
66
67# --- Closed-vector laws live in laws/MergeIter.bend (spec laws 4, 5, 10) ---