lower contention on AggregationLimits

PR quickwit-oss/quickwit#4962 fixes an issue
where the AggregationLimits are not passed correctly. Since the
AggregationLimits are shared properly we run into contention issues.

This PR includes some straightforward improvement to reduce contention,
by only calling if the memory changed and avoiding the second read.

We probably need some sharding with multiple counters or local caching before updating the
global after some threshold.

src/aggregation/agg_limits.rs

@@ -81,10 +81,11 @@ impl AggregationLimits {
         }
     }
 
-    pub(crate) fn add_memory_consumed(&self, num_bytes: u64) -> crate::Result<()> {
-        self.memory_consumption
-            .fetch_add(num_bytes, Ordering::Relaxed);
-        validate_memory_consumption(&self.memory_consumption, self.memory_limit)?;
+    pub(crate) fn add_memory_consumed(&self, add_num_bytes: u64) -> crate::Result<()> {
+        let prev_value = self
+            .memory_consumption
+            .fetch_add(add_num_bytes, Ordering::Relaxed);
+        validate_memory_consumption(prev_value + add_num_bytes, self.memory_limit)?;
         Ok(())
     }
 
@@ -94,11 +95,11 @@ impl AggregationLimits {
 }
 
 fn validate_memory_consumption(
-    memory_consumption: &AtomicU64,
+    memory_consumption: u64,
     memory_limit: ByteCount,
 ) -> Result<(), AggregationError> {
     // Load the estimated memory consumed by the aggregations
-    let memory_consumed: ByteCount = memory_consumption.load(Ordering::Relaxed).into();
+    let memory_consumed: ByteCount = memory_consumption.into();
     if memory_consumed > memory_limit {
         return Err(AggregationError::MemoryExceeded {
             limit: memory_limit,
@@ -118,10 +119,11 @@ pub struct ResourceLimitGuard {
 }
 
 impl ResourceLimitGuard {
-    pub(crate) fn add_memory_consumed(&self, num_bytes: u64) -> crate::Result<()> {
-        self.memory_consumption
-            .fetch_add(num_bytes, Ordering::Relaxed);
-        validate_memory_consumption(&self.memory_consumption, self.memory_limit)?;
+    pub(crate) fn add_memory_consumed(&self, add_num_bytes: u64) -> crate::Result<()> {
+        let prev_value = self
+            .memory_consumption
+            .fetch_add(add_num_bytes, Ordering::Relaxed);
+        validate_memory_consumption(prev_value + add_num_bytes, self.memory_limit)?;
         Ok(())
     }
 }

src/aggregation/bucket/histogram/histogram.rs

@@ -331,9 +331,11 @@ impl SegmentAggregationCollector for SegmentHistogramCollector {
         }
 
         let mem_delta = self.get_memory_consumption() - mem_pre;
-        bucket_agg_accessor
-            .limits
-            .add_memory_consumed(mem_delta as u64)?;
+        if mem_delta > 0 {
+            bucket_agg_accessor
+                .limits
+                .add_memory_consumed(mem_delta as u64)?;
+        }
 
         Ok(())
     }

src/aggregation/bucket/term_agg.rs

@@ -324,9 +324,11 @@ impl SegmentAggregationCollector for SegmentTermCollector {
         }
 
         let mem_delta = self.get_memory_consumption() - mem_pre;
-        bucket_agg_accessor
-            .limits
-            .add_memory_consumed(mem_delta as u64)?;
+        if mem_delta > 0 {
+            bucket_agg_accessor
+                .limits
+                .add_memory_consumed(mem_delta as u64)?;
+        }
 
         Ok(())
     }