limit and offset

README.md

@@ -8,9 +8,9 @@
 * [x] unification
 * [x] aggregation
 * [x] duplicate symbols in rule heads
-* [ ] limit, offset
-* [ ] range scan
-* [ ] public API
+* [x] limit, offset
+* [x] public API
 * [ ] sorting
+* [ ] range scan
 
 comparators can have problems when sorting mixed integers and floats

cozopy/cozo.py

@@ -14,10 +14,14 @@ class CozoDb:
     def tx(self, payload):
         return json.loads(self.inner.transact_triples(json.dumps({'tx': payload}, ensure_ascii=False)))
 
-    def run(self, q, out=None):
+    def run(self, q, out=None, limit=None, offset=None):
         payload = {'q': q}
         if out is not None:
             payload['out'] = out
+        if limit is not None:
+            payload['limit'] = limit
+        if offset is not None:
+            payload['offset'] = offset
         return json.loads(self.inner.run_query(json.dumps(payload, ensure_ascii=False)))
 
 

src/data/program.rs

@@ -190,6 +190,13 @@ impl MagicSymbol {
     pub(crate) fn has_bound_adornment(&self) -> bool {
         self.magic_adornment().iter().any(|b| *b)
     }
+    pub(crate) fn is_prog_entry(&self) -> bool {
+        if let MagicSymbol::Muggle { inner } = self {
+            inner.is_prog_entry()
+        } else {
+            false
+        }
+    }
 }
 
 #[derive(Debug, Clone)]

src/parse/query.rs

@@ -22,11 +22,28 @@ use crate::utils::swap_result_option;
 
 pub(crate) type OutSpec = (Vec<(usize, Option<PullSpecs>)>, Option<Vec<String>>);
 
+pub(crate) struct QueryOutOptions {
+    pub(crate) out_spec: Option<OutSpec>,
+    pub(crate) vld: Validity,
+    pub(crate) limit: Option<usize>,
+    pub(crate) offset: Option<usize>,
+}
+
+impl QueryOutOptions {
+    pub(crate) fn num_to_take(&self) -> Option<usize> {
+        match (self.limit, self.offset) {
+            (None, _) => None,
+            (Some(i), None) => Some(i),
+            (Some(i), Some(j)) => Some(i + j),
+        }
+    }
+}
+
 impl SessionTx {
     pub(crate) fn parse_query(
         &mut self,
         payload: &JsonValue,
-    ) -> Result<(InputProgram, Option<OutSpec>, Validity)> {
+    ) -> Result<(InputProgram, QueryOutOptions)> {
         let vld = match payload.get("since") {
             None => Validity::current(),
             Some(v) => Validity::try_from(v)?,
@@ -55,7 +72,25 @@ impl SessionTx {
             .get("out")
             .map(|spec| self.parse_query_out_spec(spec, entry_bindings));
         let out_spec = swap_result_option(out_spec)?;
-        Ok((input_prog, out_spec, vld))
+        let limit = swap_result_option(payload.get("limit").map(|v| {
+            v.as_u64()
+                .map(|v| v as usize)
+                .ok_or_else(|| anyhow!("'limit' must be a positive number"))
+        }))?;
+        let offset = swap_result_option(payload.get("offset").map(|v| {
+            v.as_u64()
+                .map(|v| v as usize)
+                .ok_or_else(|| anyhow!("'offset' must be a positive number"))
+        }))?;
+        Ok((
+            input_prog,
+            QueryOutOptions {
+                out_spec,
+                vld,
+                limit,
+                offset,
+            },
+        ))
     }
     fn parse_query_out_spec(
         &mut self,

src/query/eval.rs

@@ -10,11 +10,28 @@ use crate::query::compile::{AggrKind, CompiledProgram};
 use crate::runtime::temp_store::TempStore;
 use crate::runtime::transact::SessionTx;
 
+pub(crate) struct QueryLimiter {
+    limit: Option<usize>,
+    counter: usize,
+}
+
+impl QueryLimiter {
+    pub(crate) fn incr(&mut self) -> bool {
+        if let Some(limit) = self.limit {
+            self.counter += 1;
+            self.counter >= limit
+        } else {
+            false
+        }
+    }
+}
+
 impl SessionTx {
     pub(crate) fn stratified_magic_evaluate(
         &mut self,
         strata: &[CompiledProgram],
         stores: &BTreeMap<MagicSymbol, TempStore>,
+        num_to_take: Option<usize>,
     ) -> Result<TempStore> {
         let ret_area = stores
             .get(&MagicSymbol::Muggle {
@@ -25,7 +42,7 @@ impl SessionTx {
 
         for (idx, cur_prog) in strata.iter().enumerate() {
             debug!("stratum {}", idx);
-            self.semi_naive_magic_evaluate(cur_prog, &stores)?;
+            self.semi_naive_magic_evaluate(cur_prog, &stores, num_to_take)?;
         }
         Ok(ret_area)
     }
@@ -33,6 +50,7 @@ impl SessionTx {
         &mut self,
         prog: &CompiledProgram,
         stores: &BTreeMap<MagicSymbol, TempStore>,
+        num_to_take: Option<usize>,
     ) -> Result<()> {
         if log_enabled!(Level::Debug) {
             for (k, vs) in prog.iter() {
@@ -44,6 +62,10 @@ impl SessionTx {
 
         let mut changed: BTreeMap<_, _> = prog.keys().map(|k| (k, false)).collect();
         let mut prev_changed = changed.clone();
+        let mut limiter = QueryLimiter {
+            limit: num_to_take,
+            counter: 0,
+        };
 
         for epoch in 0u32.. {
             debug!("epoch {}", epoch);
@@ -52,6 +74,7 @@ impl SessionTx {
                     let aggr_kind = ruleset.aggr_kind();
                     let store = stores.get(k).unwrap();
                     let use_delta = BTreeSet::default();
+                    let should_check_limit = num_to_take.is_some() && k.is_prog_entry();
                     match aggr_kind {
                         AggrKind::None | AggrKind::Meet => {
                             let is_meet = aggr_kind == AggrKind::Meet;
@@ -63,7 +86,17 @@ impl SessionTx {
                                     if is_meet {
                                         store.aggr_meet_put(&item, &rule.aggr, 0)?;
                                     } else {
-                                        store.put(&item, 0)?;
+                                        if should_check_limit {
+                                            if !store.exists(&item, 0)? {
+                                                store.put(&item, 0)?;
+                                                if limiter.incr() {
+                                                    trace!("early stopping due to result count limit exceeded");
+                                                    return Ok(());
+                                                }
+                                            }
+                                        } else {
+                                            store.put(&item, 0)?;
+                                        }
                                     }
                                     *changed.get_mut(k).unwrap() = true;
                                 }
@@ -86,12 +119,32 @@ impl SessionTx {
                                     if rule_is_aggr {
                                         store_to_use.normal_aggr_put(&item, &rule.aggr, serial)?;
                                     } else {
-                                        store_to_use.put(&item, 0)?;
+                                        if should_check_limit {
+                                            if !store.exists(&item, 0)? {
+                                                store.put(&item, 0)?;
+                                                if limiter.incr() {
+                                                    trace!("early stopping due to result count limit exceeded");
+                                                    return Ok(());
+                                                }
+                                            }
+                                        } else {
+                                            store_to_use.put(&item, 0)?;
+                                        }
                                     }
                                     *changed.get_mut(k).unwrap() = true;
                                 }
                                 if rule_is_aggr {
-                                    store_to_use.normal_aggr_scan_and_put(&rule.aggr, store)?;
+                                    if store_to_use.normal_aggr_scan_and_put(
+                                        &rule.aggr,
+                                        store,
+                                        if should_check_limit {
+                                            Some(&mut limiter)
+                                        } else {
+                                            None
+                                        },
+                                    )? {
+                                        return Ok(());
+                                    }
                                 }
                             }
                         }
@@ -105,6 +158,7 @@ impl SessionTx {
 
                 for (k, ruleset) in prog.iter() {
                     let store = stores.get(k).unwrap();
+                    let should_check_limit = num_to_take.is_some() && k.is_prog_entry();
                     for (rule_n, rule) in ruleset.rules.iter().enumerate() {
                         let mut should_do_calculation = false;
                         for d_rule in &rule.contained_rules {
@@ -160,6 +214,12 @@ impl SessionTx {
                                         *changed.get_mut(k).unwrap() = true;
                                         store.put(&item, epoch)?;
                                         store.put(&item, 0)?;
+                                        if should_check_limit {
+                                            if limiter.incr() {
+                                                trace!("early stopping due to result count limit exceeded");
+                                                return Ok(());
+                                            }
+                                        }
                                     }
                                 }
                             }

src/query/pull.rs

@@ -1,6 +1,7 @@
 use std::collections::{BTreeSet, HashSet};
 
 use anyhow::Result;
+use either::{Left, Right};
 use itertools::Itertools;
 use serde_json::{json, Map};
 use smallvec::{smallvec, SmallVec, ToSmallVec};
@@ -14,7 +15,7 @@ use crate::data::json::JsonValue;
 use crate::data::symb::Symbol;
 use crate::data::triple::StoreOp;
 use crate::data::value::DataValue;
-use crate::parse::query::OutSpec;
+use crate::parse::query::QueryOutOptions;
 use crate::query::relation::flatten_err;
 use crate::runtime::temp_store::TempStore;
 use crate::runtime::transact::SessionTx;
@@ -86,18 +87,20 @@ impl SessionTx {
     pub(crate) fn run_pull_on_query_results(
         &mut self,
         res_store: TempStore,
-        out_spec: Option<OutSpec>,
-        vld: Validity,
+        out_opts: QueryOutOptions,
     ) -> Result<QueryResult<'_>> {
-        match out_spec {
-            None => Ok(Box::new(res_store.scan_all().map_ok(|tuple| {
+        let out_iter = match out_opts.offset {
+            None => Left(res_store.scan_all()),
+            Some(n) => Right(res_store.scan_all().skip(n)),
+        };
+        match out_opts.out_spec {
+            None => Ok(Box::new(out_iter.map_ok(|tuple| {
                 JsonValue::Array(tuple.0.into_iter().map(JsonValue::from).collect_vec())
             }))),
             Some((pull_specs, out_keys)) => {
                 // type OutSpec = (Vec<(usize, Option<PullSpecs>)>, Option<Vec<String>>);
                 Ok(Box::new(
-                    res_store
-                        .scan_all()
+                    out_iter
                         .map_ok(move |tuple| -> Result<JsonValue> {
                             let tuple = tuple.0;
                             let res_iter =
@@ -115,7 +118,7 @@ impl SessionTx {
                                             for (idx, spec) in specs.iter().enumerate() {
                                                 self.pull(
                                                     eid,
-                                                    vld,
+                                                    out_opts.vld,
                                                     spec,
                                                     0,
                                                     &specs,

src/runtime/db.rs

@@ -280,21 +280,21 @@ impl Db {
     }
     pub fn run_query(&self, payload: &JsonValue) -> Result<JsonValue> {
         let mut tx = self.transact()?;
-        let (input_program, out_spec, vld) = tx.parse_query(payload)?;
+        let (input_program, out_opts) = tx.parse_query(payload)?;
         let program = input_program
             .to_normalized_program()?
             .stratify()?
             .magic_sets_rewrite();
         let (compiled, stores) = tx.stratified_magic_compile(&program)?;
-        let result = tx.stratified_magic_evaluate(&compiled, &stores)?;
+        let result = tx.stratified_magic_evaluate(&compiled, &stores, out_opts.num_to_take())?;
         let ret: Vec<_> = tx
-            .run_pull_on_query_results(result, out_spec, vld)?
+            .run_pull_on_query_results(result, out_opts)?
             .try_collect()?;
         Ok(json!(ret))
     }
     pub fn explain_query(&self, payload: &JsonValue) -> Result<JsonValue> {
         let mut tx = self.transact()?;
-        let (input_program, out_spec, vld) = tx.parse_query(payload)?;
+        let (input_program, out_opts) = tx.parse_query(payload)?;
         let normalized_program = input_program.to_normalized_program()?;
         let stratified_program = normalized_program.stratify()?;
         let magic_program = stratified_program.magic_sets_rewrite();

src/runtime/temp_store.rs

@@ -1,3 +1,4 @@
+use std::borrow::BorrowMut;
 use std::fmt::{Debug, Formatter};
 
 use anyhow::Result;
@@ -10,6 +11,7 @@ use crate::data::aggr::Aggregation;
 use crate::data::program::MagicSymbol;
 use crate::data::tuple::{EncodedTuple, Tuple};
 use crate::data::value::DataValue;
+use crate::query::eval::QueryLimiter;
 use crate::utils::swap_result_option;
 
 #[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
@@ -147,7 +149,8 @@ impl TempStore {
         &self,
         aggrs: &[Option<Aggregation>],
         store: &TempStore,
-    ) -> Result<()> {
+        mut limiter: Option<&mut QueryLimiter>
+    ) -> Result<bool> {
         let (lower, upper) = EncodedTuple::bounds_for_prefix_and_epoch(self.id, 0);
         let mut it = self
             .db
@@ -214,12 +217,22 @@ impl TempStore {
                         }
                     }
                 }
-                store.put(&Tuple(aggr_res), 0)?;
+                let res_tpl = Tuple(aggr_res);
+                if let Some(lmt) = limiter.borrow_mut() {
+                    if !store.exists(&res_tpl, 0)? {
+                        store.put(&res_tpl, 0)?;
+                        if lmt.incr() {
+                            return Ok(true);
+                        }
+                    }
+                } else {
+                    store.put(&res_tpl, 0)?;
+                }
             } else {
-                return group.into_iter().next().unwrap().map(|_| ());
+                return group.into_iter().next().unwrap().map(|_| true);
             }
         }
-        Ok(())
+        Ok(false)
     }
 
     pub(crate) fn scan_all_for_epoch(

tests/creation.rs

@@ -159,7 +159,8 @@ fn creation() {
                 ]
             }
         ],
-        "out": {"friend": {"pull": "?a", "spec": ["person.first_name"]}}
+        "out": {"friend": {"pull": "?a", "spec": ["person.first_name"]}},
+        "limit": 1,
     });
     let ret = db.run_query(&query).unwrap();
     let res = to_string_pretty(&ret).unwrap();