fix(storage/events): add upper bounds on queries used to select strategy

Since we already have a cost limit on the event queries there's no point
in counting the exact number of matching events by the keys or range.

It's sufficient to be able to count up to reaching a limit where the
cost would be too much anyway.

This avoids issues with queries using keys of which there are a few
hundred million events in the database.

crates/storage/src/connection/event.rs

@@ -12,6 +12,10 @@ pub const PAGE_SIZE_LIMIT: usize = 1_024;
 pub const KEY_FILTER_LIMIT: usize = 256;
 
 const KEY_FILTER_COST_LIMIT: usize = 1_000_000;
+const KEY_FILTER_WEIGHT: usize = 50;
+
+const KEY_FILTER_UPPER_BOUND: usize = KEY_FILTER_COST_LIMIT / KEY_FILTER_WEIGHT;
+const RANGE_FILTER_UPPER_BOUND: usize = KEY_FILTER_COST_LIMIT;
 
 pub struct EventFilter<K: KeyFilter> {
     pub from_block: Option<BlockNumber>,
@@ -347,8 +351,8 @@ impl KeyFilter for V03KeyFilter {
             None => Ok(None),
             Some(key_fts_expression) => {
                 let count: usize = tx.inner().query_row(
-                    "SELECT COUNT(1) FROM starknet_events_keys_03 WHERE keys MATCH :events_match",
-                    [&key_fts_expression],
+                    "SELECT COUNT(1) FROM (SELECT 1 FROM starknet_events_keys_03 WHERE keys MATCH :events_match LIMIT :limit)",
+                    params!(key_fts_expression, &(KEY_FILTER_UPPER_BOUND as u64)),
                     |row| row.get(0),
                 )?;
                 Ok(Some(count))
@@ -472,7 +476,8 @@ fn select_query_strategy(
     let events_by_key_filter = number_of_events_by_key_filter(tx, keys)?;
     if let Some(events_by_key_filter) = events_by_key_filter {
         // shortcut if the key filter is specific enough
-        if events_by_key_filter < 100_000 {
+        // KEY_FILTER_UPPER_BOUND really means >= KEY_FILTER_UPPER_BOUND
+        if events_by_key_filter < KEY_FILTER_UPPER_BOUND {
             tracing::trace!(
                 %events_by_key_filter,
                 "Partial queries for number of events done"
@@ -493,7 +498,6 @@ fn select_query_strategy(
         "Partial queries for number of events done"
     );
 
-    const KEY_FILTER_WEIGHT: usize = 50;
     let weighted_events_by_key_filter =
         events_by_key_filter.map(|n| n.saturating_mul(KEY_FILTER_WEIGHT));
 
@@ -536,7 +540,7 @@ fn number_of_events_in_block_range(
     to_block: Option<&BlockNumber>,
     contract_address: Option<&ContractAddress>,
 ) -> anyhow::Result<Option<usize>> {
-    let mut query = "SELECT COUNT(1) FROM starknet_events WHERE ".to_owned();
+    let mut query = "SELECT COUNT(1) FROM (SELECT 1 FROM starknet_events WHERE ".to_owned();
     let mut params: Vec<(&str, rusqlite::types::ToSqlOutput<'_>)> = Vec::new();
 
     match (from_block, to_block) {
@@ -566,6 +570,9 @@ fn number_of_events_in_block_range(
         params.push((":contract_address", contract_address.to_sql()));
     }
 
+    query.push_str(" LIMIT :limit)");
+    params.push((":limit", (RANGE_FILTER_UPPER_BOUND as u64).to_sql()));
+
     let params = params
         .iter()
         .map(|(s, x)| (*s, x as &dyn rusqlite::ToSql))