perf(hash agg): use get_mut instead of pop+put pattern (risingwavelabs#8691)

Signed-off-by: Richard Chien <[email protected]>

Author: stdrc

src/stream/src/executor/hash_agg.rs

@@ -14,6 +14,7 @@
 
 use std::collections::{HashMap, HashSet};
 use std::marker::PhantomData;
+use std::ptr::NonNull;
 use std::sync::Arc;
 
 use futures::{stream, StreamExt, TryStreamExt};
@@ -436,11 +437,17 @@ impl<K: HashKey, S: StateStore> HashAggExecutor<K, S> {
 
                 // Calculate current outputs, concurrently.
                 let futs = keys_in_batch.into_iter().map(|key| {
-                    // Pop out the agg group temporarily.
-                    let mut agg_group = vars
-                        .agg_group_cache
-                        .pop(&key)
-                        .expect("changed group must have corresponding AggGroup");
+                    // Get agg group of the key.
+                    let agg_group = {
+                        let mut ptr: NonNull<_> = vars
+                            .agg_group_cache
+                            .get_mut(&key)
+                            .expect("changed group must have corresponding AggGroup")
+                            .into();
+                        // SAFETY: `key`s in `keys_in_batch` are unique by nature, because they're
+                        // from `group_change_set` which is a set.
+                        unsafe { ptr.as_mut() }
+                    };
                     async {
                         let curr_outputs = agg_group.get_outputs(&this.storages).await?;
                         Ok::<_, StreamExecutorError>((key, agg_group, curr_outputs))
@@ -452,7 +459,7 @@ impl<K: HashKey, S: StateStore> HashAggExecutor<K, S> {
                     .try_collect()
                     .await?;
 
-                for (key, mut agg_group, curr_outputs) in outputs_in_batch {
+                for (key, agg_group, curr_outputs) in outputs_in_batch {
                     let AggChangesInfo {
                         n_appended_ops,
                         result_row,
@@ -477,9 +484,6 @@ impl<K: HashKey, S: StateStore> HashAggExecutor<K, S> {
                             this.result_table.insert(result_row);
                         }
                     }
-
-                    // Put the agg group back into the agg group cache.
-                    vars.agg_group_cache.put(key, agg_group);
                 }
 
                 let columns = builders