Use a single key to store deltas

To improve the distribution of the stored deltas, we removed the deep
key value maps and use a custom key to encode the `context` and
`timestamp` of a stored delta. Thus, improving the amount of data
that needs to be loaded for each operation.

Added additional end-to-end tests and benchmarks to validate the
behavior.

benches/query.rs

@@ -126,3 +126,36 @@ fn bench_apply_deltas(b: &mut Bencher) {
         });
     });
 }
+
+#[bench]
+fn bench_apply_deltas_with_multiple_dates(b: &mut Bencher) {
+    let mut deltas = Vec::new();
+
+    deltas.extend(decrease_score_deltas(&PLAYERS, COUNT));
+    deltas.extend(switch_sports_deltas(&PLAYERS, COUNT));
+
+    let mut date: Date = *DATE;
+
+    tokio_test::block_on(async {
+        for delta_chunk in deltas.chunks(10) {
+            ENGINE
+                .store_deltas(&NAME, &DeltaScope::date(date), delta_chunk)
+                .await
+                .unwrap();
+
+            date = date.next_day().unwrap();
+        }
+    });
+
+    b.iter(move || {
+        tokio_test::block_on(async {
+            let scope = DeltaScope::date(date.next_day().unwrap());
+
+            let query = QueryExecution::new()
+                .with_scope(scope)
+                .with_pagination(*PAGINATION);
+
+            ENGINE.query(&NAME, query).await.unwrap();
+        });
+    });
+}

examples/simple.rs

@@ -1,7 +1,7 @@
 use delta_search::data::FieldValue;
 use delta_search::fixtures::{
-    create_players_storage, cristiano_ronaldo, david, lionel_messi, michael_jordan, roger, Sport,
-    SwitchSportsDelta,
+    create_players_storage, cristiano_ronaldo, david, lionel_messi, michael_jordan, roger,
+    DecreaseScoreDelta, Sport, SwitchSportsDelta,
 };
 use delta_search::query::{
     CompositeFilter, DeltaScope, OptionsQueryExecution, QueryExecution, Sort, SortDirection,
@@ -50,7 +50,7 @@ async fn main() {
         .with_sort(Sort::new("score").with_direction(SortDirection::DESC));
     let players = engine.query(name, query).await;
 
-    println!("Basketball players sorted by score: {:?}", players);
+    println!("Basketball players sorted by score:\n{:?}\n", players);
 
     let players = engine
         .query(
@@ -65,7 +65,7 @@ async fn main() {
         )
         .await;
 
-    println!("Players born in the 80s: {:?}", players);
+    println!("Players born in the 80s:\n{:?}\n", players);
 
     let switch_sports = vec![
         SwitchSportsDelta::create(michael_jordan_id, Sport::Basketball, Sport::Football),
@@ -92,8 +92,37 @@ async fn main() {
     let players = engine.query(name, query).await;
 
     println!(
-        "Basketball players sorted by score after switching sports in 2023: {:?}",
-        players
+        "Basketball players sorted by score after switching sports in 2023:\n{:?}\n",
+        players.unwrap()
+    );
+
+    let lower_scores = vec![
+        DecreaseScoreDelta::create(michael_jordan_id, 10.0),
+        DecreaseScoreDelta::create(lionel_messi_id, 9.0),
+    ];
+
+    let delta_scope = DeltaScope::context(
+        0,
+        Date::from_calendar_date(2023, Month::January, 1).unwrap(),
+    );
+
+    engine
+        .store_deltas(name, &delta_scope, &lower_scores)
+        .await
+        .unwrap();
+
+    let query = QueryExecution::new()
+        .with_sort(Sort::new("score").with_direction(SortDirection::DESC))
+        .with_scope(DeltaScope::context(
+            0,
+            Date::from_calendar_date(2024, Month::January, 1).unwrap(),
+        ));
+
+    let players = engine.query(name, query).await;
+
+    println!(
+        "Players sorted by score after decreasing their score by 1:\n{:?}\n",
+        players.unwrap()
     );
 
     engine.remove(name, &david_id).await.unwrap();
@@ -108,5 +137,8 @@ async fn main() {
         )
         .await;
 
-    println!("Players playing basketball after deletion: {:?}", players);
+    println!(
+        "Players playing basketball after deletion:\n{:?}\n",
+        players.unwrap()
+    );
 }

src/fixtures.rs

@@ -270,7 +270,7 @@ impl Player {
 pub struct DecreaseScoreDelta;
 
 impl DecreaseScoreDelta {
-    pub(crate) fn create(id: DataItemId, score: f64) -> DeltaChange {
+    pub fn create(id: DataItemId, score: f64) -> DeltaChange {
         DeltaChange::new(
             id,
             "score".to_string(),

src/main.rs

@@ -330,7 +330,7 @@ fn parse_date(string: &str) -> Result<Date, time::error::Parse> {
 #[derive(Deserialize)]
 #[serde(rename_all = "camelCase")]
 struct DeltaScopeInput {
-    context: Option<u64>,
+    context: Option<u32>,
     date: String,
 }
 

src/query.rs

@@ -25,12 +25,12 @@ impl FilterOption {
 
 #[derive(Debug, PartialEq, Deserialize)]
 pub struct DeltaScope {
-    pub(crate) context: Option<u64>,
+    pub(crate) context: Option<u32>,
     pub(crate) date: Date,
 }
 
 impl DeltaScope {
-    pub fn new(context: Option<u64>, date: Date) -> Self {
+    pub fn new(context: Option<u32>, date: Date) -> Self {
         Self { context, date }
     }
 
@@ -41,7 +41,7 @@ impl DeltaScope {
         }
     }
 
-    pub fn context(context: u64, date: Date) -> Self {
+    pub fn context(context: u32, date: Date) -> Self {
         DeltaScope {
             context: Some(context),
             date,