Database thread pool use (#14498)

Co-authored-by: metalgearsloth <comedian_vs_clown@hotmail.com>

Content.Shared/CCVar/CCVars.cs

@@ -449,6 +449,17 @@ namespace Content.Shared.CCVar
         public static readonly CVarDef<int> DatabaseSqliteDelay =
             CVarDef.Create("database.sqlite_delay", DefaultSqliteDelay, CVar.SERVERONLY);
 
+        /// <summary>
+        /// Amount of concurrent SQLite database operations.
+        /// </summary>
+        /// <remarks>
+        /// Note that SQLite is not a properly asynchronous database and also has limited read/write concurrency.
+        /// Increasing this number may allow more concurrent reads, but it probably won't matter much.
+        /// SQLite operations are normally ran on the thread pool, which may cause thread pool starvation if the concurrency is too high.
+        /// </remarks>
+        public static readonly CVarDef<int> DatabaseSqliteConcurrency =
+            CVarDef.Create("database.sqlite_concurrency", 3, CVar.SERVERONLY);
+
 #if DEBUG
         private const int DefaultSqliteDelay = 1;
 #else