kevy_index/
segment.rs

1//! [`Segment`] — one shard's slice of one index (index-follows-key).
2//! Range = `BTreeSet<(value, key)>`; Unique = the same
3//! tree (point lookups are a 1-value range) plus a duplicate counter
4//! for the declarative fence.
5//!
6//! The runtime keeps a reverse map `key → value` inside the segment so
7//! `apply` can remove a row's OLD entry without re-reading history.
8
9use std::collections::BTreeMap;
10use std::collections::BTreeSet;
11use std::collections::HashMap;
12use std::ops::Bound;
13
14use crate::rowvalues::RowValues;
15use crate::value::IndexValue;
16
17/// Opaque pagination cursor: the last `(value, key)` served. Encoded
18/// by the runtime into the wire cursor; `None` = start.
19#[derive(Debug, Clone, PartialEq, Eq)]
20pub struct Cursor {
21    /// Last value served.
22    pub value: IndexValue,
23    /// Last key served (tiebreak within a value).
24    pub key: Vec<u8>,
25}
26
27/// Sizing + health counters (`IDX.LIST` / memory formula).
28#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
29pub struct SegmentStats {
30    /// Live entries.
31    pub entries: u64,
32    /// Approximate heap bytes (the measured side of the documented
33    /// memory formula).
34    pub approx_bytes: u64,
35    /// Rows excluded because the field failed coercion / was missing.
36    pub coerce_failures: u64,
37    /// Values currently held by more than one key (unique fence).
38    pub duplicates: u64,
39}
40
41/// Per-entry structural overhead in the memory formula.
42const ENTRY_OVERHEAD: usize = 48;
43
44/// One shard's slice of one index.
45#[derive(Debug, Default)]
46pub struct Segment {
47    tree: BTreeSet<(IndexValue, Vec<u8>)>,
48    back: HashMap<Vec<u8>, IndexValue>,
49    value_counts: BTreeMap<IndexValue, u32>,
50    stats: SegmentStats,
51    /// The stored-value side-channel — `Some` only when the index
52    /// declared `VALUES`. An index without the declaration holds `None`
53    /// and pays nothing: every values touch below is a never-taken
54    /// `if let` (the `Option<Positions>` physical-bypass pattern, A5).
55    values: Option<RowValues>,
56}
57
58impl Segment {
59    /// Empty segment.
60    pub fn new() -> Self {
61        Self::default()
62    }
63
64    /// Empty segment carrying the stored-value side-channel for `n`
65    /// declared `VALUES` fields (`n` = the spec's `values.len()`).
66    pub fn with_values(n: usize) -> Self {
67        Segment { values: Some(RowValues::new(n)), ..Self::default() }
68    }
69
70    /// [`Segment::apply`] plus the row's declared stored values. The
71    /// values follow the entry: an indexed row stores them, an excluded
72    /// or deleted one drops them.
73    pub fn apply_with_values(
74        &mut self,
75        key: &[u8],
76        new: Option<IndexValue>,
77        vals: &[Option<&[u8]>],
78    ) {
79        let indexed = new.is_some();
80        self.apply(key, new);
81        if let Some(rv) = &mut self.values {
82            if indexed {
83                rv.set(key, vals);
84            } else {
85                rv.clear(key);
86            }
87        }
88    }
89
90    /// `key`'s stored value for declared `VALUES` field `field`, or
91    /// `None` when the row has none (or the index declared none).
92    pub fn stored(&self, key: &[u8], field: usize) -> Option<&[u8]> {
93        self.values.as_ref()?.get(key, field)
94    }
95
96    /// Every stored value of one row, aligned with the declared
97    /// `VALUES` order — what an eviction carries into a cold entry's
98    /// payload so the clause-carrying cold path never re-reads the
99    /// row. Empty when the index declared no values.
100    pub fn stored_row(&self, key: &[u8]) -> Vec<Option<&[u8]>> {
101        match self.values.as_ref() {
102            Some(rv) => (0..rv.arity()).map(|f| rv.get(key, f)).collect(),
103            None => Vec::new(),
104        }
105    }
106
107    /// The `(value, key)` tree, for the clause-carrying scan.
108    pub(crate) fn tree(&self) -> &BTreeSet<(IndexValue, Vec<u8>)> {
109        &self.tree
110    }
111
112    /// Synchronous write-path maintenance: the row at `key` now
113    /// coerces to `new` (`None` = excluded / row deleted). Replaces
114    /// any previous entry for the key.
115    pub fn apply(&mut self, key: &[u8], new: Option<IndexValue>) {
116        if let Some(old) = self.back.remove(key) {
117            self.tree.remove(&(old.clone(), key.to_vec()));
118            self.stats.entries -= 1;
119            self.stats.approx_bytes = self
120                .stats
121                .approx_bytes
122                .saturating_sub((old.approx_bytes() + key.len() + ENTRY_OVERHEAD) as u64);
123            self.dec_count(&old);
124        }
125        match new {
126            Some(v) => {
127                self.stats.entries += 1;
128                self.stats.approx_bytes += (v.approx_bytes() + key.len() + ENTRY_OVERHEAD) as u64;
129                self.inc_count(&v);
130                self.back.insert(key.to_vec(), v.clone());
131                self.tree.insert((v, key.to_vec()));
132            }
133            None => {
134                self.stats.coerce_failures += 1;
135            }
136        }
137    }
138
139    /// The largest value present, if any — the window boundary's
140    /// tree-tail read.
141    pub fn max_value(&self) -> Option<&IndexValue> {
142        self.tree.last().map(|(v, _)| v)
143    }
144
145    /// Entries strictly below `bound`, tree order — the read-only
146    /// preview of [`Self::split_off_below`]'s batch (the slide builds
147    /// its segment from this BEFORE cutting, so an I/O failure leaves
148    /// the tree untouched).
149    pub fn iter_below(&self, bound: &IndexValue) -> impl Iterator<Item = (&IndexValue, &[u8])> {
150        let end = (bound.clone(), Vec::new());
151        self.tree
152            .range((core::ops::Bound::Unbounded, core::ops::Bound::Excluded(end)))
153            .map(|(v, k)| (v, k.as_slice()))
154    }
155
156    /// Detach every entry whose value sorts below `bound`, in tree
157    /// order — the window-eviction cut. The detached batch leaves all
158    /// of the segment's books (tree, reverse map, value counts, stored
159    /// values, stats) exactly as if each entry had been removed one by
160    /// one; the empty-key sentinel keeps every entry AT `bound` in the
161    /// hot tree, so the cut is strictly `< bound`.
162    pub fn split_off_below(&mut self, bound: &IndexValue) -> Vec<(IndexValue, Vec<u8>)> {
163        let kept = self.tree.split_off(&(bound.clone(), Vec::new()));
164        let evicted: Vec<(IndexValue, Vec<u8>)> =
165            core::mem::replace(&mut self.tree, kept).into_iter().collect();
166        for (v, k) in &evicted {
167            self.back.remove(k);
168            self.stats.entries -= 1;
169            self.stats.approx_bytes = self
170                .stats
171                .approx_bytes
172                .saturating_sub((v.approx_bytes() + k.len() + ENTRY_OVERHEAD) as u64);
173            self.dec_count(v);
174            if let Some(rv) = &mut self.values {
175                rv.clear(k);
176            }
177        }
178        evicted
179    }
180
181    /// Row deleted (no coercion involved — not a coerce failure).
182    pub fn remove(&mut self, key: &[u8]) {
183        if let Some(rv) = &mut self.values {
184            rv.clear(key);
185        }
186        if let Some(old) = self.back.remove(key) {
187            self.tree.remove(&(old.clone(), key.to_vec()));
188            self.stats.entries -= 1;
189            self.stats.approx_bytes = self
190                .stats
191                .approx_bytes
192                .saturating_sub((old.approx_bytes() + key.len() + ENTRY_OVERHEAD) as u64);
193            self.dec_count(&old);
194        }
195    }
196
197    fn inc_count(&mut self, v: &IndexValue) {
198        let c = self.value_counts.entry(v.clone()).or_insert(0);
199        *c += 1;
200        if *c == 2 {
201            self.stats.duplicates += 1;
202        }
203    }
204
205    fn dec_count(&mut self, v: &IndexValue) {
206        if let Some(c) = self.value_counts.get_mut(v) {
207            if *c == 2 {
208                self.stats.duplicates -= 1;
209            }
210            *c -= 1;
211            if *c == 0 {
212                self.value_counts.remove(v);
213            }
214        }
215    }
216
217    /// Ordered scan of `[min, max]` (inclusive), resuming after
218    /// `cursor`, up to `limit` hits. Returns `(key, value)` pairs in
219    /// `(value, key)` order plus the cursor to resume from (`None` =
220    /// exhausted).
221    pub fn range(
222        &self,
223        min: &IndexValue,
224        max: &IndexValue,
225        cursor: Option<&Cursor>,
226        limit: usize,
227    ) -> (Vec<(Vec<u8>, IndexValue)>, Option<Cursor>) {
228        let lower: Bound<(IndexValue, Vec<u8>)> = match cursor {
229            Some(c) => Bound::Excluded((c.value.clone(), c.key.clone())),
230            None => Bound::Included((min.clone(), Vec::new())),
231        };
232        // Upper bound is exact via take-while — a synthetic sentinel
233        // key would MISS max-valued keys sorting above it.
234        let mut out = Vec::with_capacity(limit.min(64));
235        let mut iter = self.tree.range((lower, Bound::Unbounded));
236        for (v, k) in iter.by_ref() {
237            if v > max {
238                break;
239            }
240            out.push((k.clone(), v.clone()));
241            if out.len() == limit {
242                break;
243            }
244        }
245        let next = if out.len() == limit {
246            out.last().map(|(k, v)| Cursor { value: v.clone(), key: k.clone() })
247        } else {
248            None
249        };
250        (out, next)
251    }
252
253    /// Point lookup: every key holding exactly `value` (unique kind's
254    /// read; >1 hit = the declarative fence's `-DUPLICATE` signal).
255    pub fn eq(&self, value: &IndexValue, limit: usize) -> Vec<Vec<u8>> {
256        let lower = Bound::Included((value.clone(), Vec::new()));
257        self.tree
258            .range((lower, Bound::Unbounded))
259            .take_while(|(v, _)| v == value)
260            .take(limit)
261            .map(|(_, k)| k.clone())
262            .collect()
263    }
264
265    /// Count within `[min, max]` without materializing keys.
266    pub fn count(&self, min: &IndexValue, max: &IndexValue) -> u64 {
267        let lower = Bound::Included((min.clone(), Vec::new()));
268        self.tree.range((lower, Bound::Unbounded)).take_while(|(v, _)| v <= max).count() as u64
269    }
270
271    /// Verify hook: what value does the segment hold for `key`?
272    /// (`IDX.VERIFY` compares this against a fresh row coercion.)
273    pub fn verify_entry(&self, key: &[u8]) -> Option<&IndexValue> {
274        self.back.get(key)
275    }
276
277    /// Ordered streaming scan over the WHOLE segment: ascending (or
278    /// descending) `(value, key)` order, resuming exclusively past
279    /// `after`. The virtual-view pager drives this and probes
280    /// membership per candidate — O(limit × selectivity⁻¹) instead of
281    /// materializing the full member set.
282    pub fn scan<'s>(
283        &'s self,
284        after: Option<&Cursor>,
285        desc: bool,
286    ) -> Box<dyn Iterator<Item = (&'s IndexValue, &'s [u8])> + 's> {
287        match (after, desc) {
288            (None, false) => Box::new(self.tree.iter().map(|(v, k)| (v, k.as_slice()))),
289            (None, true) => Box::new(self.tree.iter().rev().map(|(v, k)| (v, k.as_slice()))),
290            (Some(c), false) => Box::new(
291                self.tree
292                    .range((Bound::Excluded((c.value.clone(), c.key.clone())), Bound::Unbounded))
293                    .map(|(v, k)| (v, k.as_slice())),
294            ),
295            (Some(c), true) => Box::new(
296                self.tree
297                    .range((Bound::Unbounded, Bound::Excluded((c.value.clone(), c.key.clone()))))
298                    .rev()
299                    .map(|(v, k)| (v, k.as_slice())),
300            ),
301        }
302    }
303
304    /// Visit every `(key, value)` entry (verify / audit walks).
305    pub fn each_entry<F: FnMut(&[u8], &IndexValue)>(&self, mut f: F) {
306        for (k, v) in &self.back {
307            f(k.as_slice(), v);
308        }
309    }
310
311    /// Live counters. The stored-value column's heap joins the memory
312    /// term when (and only when) the index declared `VALUES`.
313    pub fn stats(&self) -> SegmentStats {
314        let mut s = self.stats;
315        if let Some(rv) = &self.values {
316            s.approx_bytes += rv.approx_bytes();
317        }
318        s
319    }
320}
321
322#[cfg(test)]
323mod tests {
324    use super::*;
325
326    fn i(v: i64) -> IndexValue {
327        IndexValue::I64(v)
328    }
329
330    fn seeded() -> Segment {
331        let mut s = Segment::new();
332        for (k, v) in [("u1", 30), ("u2", 25), ("u3", 30), ("u4", 40), ("u5", 18)] {
333            s.apply(k.as_bytes(), Some(i(v)));
334        }
335        s
336    }
337
338    #[test]
339    fn apply_replace_remove_and_stats() {
340        let mut s = seeded();
341        assert_eq!(s.stats().entries, 5);
342        assert_eq!(s.stats().duplicates, 1, "30 held twice");
343        // replace u1's value: 30 no longer duplicated
344        s.apply(b"u1", Some(i(31)));
345        assert_eq!(s.stats().entries, 5);
346        assert_eq!(s.stats().duplicates, 0);
347        // coerce-failure excludes and counts
348        s.apply(b"u2", None);
349        assert_eq!(s.stats().entries, 4);
350        assert_eq!(s.stats().coerce_failures, 1);
351        // remove is not a coerce failure
352        s.remove(b"u3");
353        assert_eq!(s.stats().entries, 3);
354        assert_eq!(s.stats().coerce_failures, 1);
355        assert!(s.verify_entry(b"u3").is_none());
356        assert_eq!(s.verify_entry(b"u4"), Some(&i(40)));
357    }
358
359    #[test]
360    fn range_scan_orders_and_paginates() {
361        let s = seeded();
362        let (page1, cur) = s.range(&i(18), &i(30), None, 2);
363        assert_eq!(page1[0], (b"u5".to_vec(), i(18)));
364        assert_eq!(page1[1], (b"u2".to_vec(), i(25)));
365        let cur = cur.expect("more pages");
366        let (page2, cur2) = s.range(&i(18), &i(30), Some(&cur), 10);
367        assert_eq!(
368            page2,
369            vec![(b"u1".to_vec(), i(30)), (b"u3".to_vec(), i(30))],
370            "value tie broken by key"
371        );
372        assert!(cur2.is_none(), "exhausted");
373        assert_eq!(s.count(&i(18), &i(30)), 4);
374        assert_eq!(s.count(&i(99), &i(100)), 0);
375    }
376
377    #[test]
378    fn eq_and_duplicate_fence() {
379        let s = seeded();
380        assert_eq!(s.eq(&i(30), 10), vec![b"u1".to_vec(), b"u3".to_vec()]);
381        assert_eq!(s.eq(&i(40), 10), vec![b"u4".to_vec()]);
382        assert!(s.eq(&i(99), 10).is_empty());
383    }
384
385    #[test]
386    fn long_keys_at_max_value_not_missed() {
387        let mut s = Segment::new();
388        let long_key = vec![0xFFu8; 80]; // sorts above any 64-byte sentinel
389        s.apply(&long_key, Some(i(30)));
390        s.apply(b"short", Some(i(30)));
391        let (hits, _) = s.range(&i(30), &i(30), None, 10);
392        assert_eq!(hits.len(), 2, "max-valued long key must not be missed");
393        assert_eq!(s.eq(&i(30), 10).len(), 2);
394        assert_eq!(s.count(&i(30), &i(30)), 2);
395    }
396
397    #[test]
398    fn f64_and_str_orders() {
399        let mut s = Segment::new();
400        s.apply(b"a", Some(IndexValue::F64(1.5)));
401        s.apply(b"b", Some(IndexValue::F64(-0.5)));
402        let (hits, _) = s.range(&IndexValue::F64(-1.0), &IndexValue::F64(2.0), None, 10);
403        assert_eq!(hits[0].0, b"b".to_vec());
404
405        let mut t = Segment::new();
406        t.apply(b"x", Some(IndexValue::Str(b"banana".to_vec())));
407        t.apply(b"y", Some(IndexValue::Str(b"apple".to_vec())));
408        let (hits, _) =
409            t.range(&IndexValue::Str(b"a".to_vec()), &IndexValue::Str(b"z".to_vec()), None, 10);
410        assert_eq!(hits[0].0, b"y".to_vec());
411    }
412}
kevy_index/segment.rs

kevy_index/
segment.rs
