Change default to 32, add documentation on option

aggregator/src/binaries/aggregator.rs

@@ -373,7 +373,7 @@ pub struct Config {
 }
 
 fn default_task_counter_shard_count() -> u64 {
-    1
+    32
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]

docs/samples/advanced_config/aggregator.yaml

@@ -97,6 +97,11 @@ max_upload_batch_write_delay_ms: 250
 # than the equivalent setting in the collection job driver. (required)
 batch_aggregation_shard_count: 32
 
+# Number of sharded database records per task counter. Increasing this value will reduce the amount
+# of database contention during report uploads, while increasing the cost of getting task metrics.
+# (optional, default: 32)
+task_counter_shard_count: 32
+
 # Configuration for the taskprov extension. If enabled, this changes the behavior of the
 # aggregator as described in draft-wang-ppm-dap-taskprov. (optional)
 taskprov_config: