fix: increase RocksDB background threads (#3156)

* increase RocksDB background threads

* update example config

---------

Co-authored-by: Markus Legner <markus@mystenlabs.com>

Author: halfprice

crates/walrus-service/node_config_example.yaml

@@ -8,7 +8,8 @@ db_config:
     keep_log_file_num: 50
     wal_ttl_seconds: 172800
     wal_size_limit_mb: 10240
-    enable_statistics: false
+    max_background_jobs: 16
+    enable_statistics: true
     use_optimistic_transaction_db: true
   standard:
     enable_blob_files: false

crates/walrus-service/src/node/storage/database_config.rs

@@ -228,6 +228,8 @@ pub struct GlobalDatabaseOptions {
     pub wal_ttl_seconds: Option<u64>,
     /// The size limit for the WAL in MB.
     pub wal_size_limit_mb: Option<u64>,
+    /// The maximum number of background jobs (compactions + flushes).
+    pub max_background_jobs: Option<i32>,
     /// Whether to enable statistics.
     pub enable_statistics: bool,
     /// If true, databases are opened using `OptimisticTransactionDB` instead of the standard DB.
@@ -244,7 +246,8 @@ impl Default for GlobalDatabaseOptions {
             keep_log_file_num: Some(50),
             wal_ttl_seconds: Some(60 * 60 * 24 * 2), // 2 days,
             wal_size_limit_mb: Some(10 * 1024),      // 10 GB,
-            enable_statistics: false,
+            max_background_jobs: Some(16),
+            enable_statistics: true,
             use_optimistic_transaction_db: true,
         }
     }
@@ -282,6 +285,10 @@ impl From<&GlobalDatabaseOptions> for Options {
             options.set_wal_size_limit_mb(wal_size_limit_mb);
         }
 
+        if let Some(max_background_jobs) = value.max_background_jobs {
+            options.set_max_background_jobs(max_background_jobs);
+        }
+
         if value.enable_statistics {
             options.enable_statistics();
             options.set_statistics_level(StatsLevel::ExceptHistogramOrTimers);