Aerospike partition tree的内存管理

as_namespaces_init：

1、uint32_t stage_capacity = as_mem_check()
     for (capacity = MAX_STAGE_CAPACITY; capacity >= MIN_STAGE_CAPACITY; capacity /= 2) {
         if (check_capacity(capacity)) {
             break;
         }
     }      

    申请的内存大小以16M开始，如果内存大小不够用，则申请16/2M依次类推，最小大小是2M

2、as_namespaces_setup(cold_start_cmd, instance, stage_capacity);
     ->setup_namespace(g_config.namespaces[i], stage_capacity);
     ->ns->arena = (cf_arenax*)cf_malloc(cf_arenax_sizeof());
       cf_arenax_err arena_result = cf_arenax_create(ns->arena, 0, 
         as_index_size_get(ns), stage_capacity, 0, CF_ARENAX_BIGLOCK);
     ->uint64_t stage_size = (uint64_t)stage_capacity * sizeof(as_index);
       memset(this->stages, 0, sizeof(this->stages));
       uint8_t* p_stage = (uint8_t*)cf_malloc(this->stage_size);
       this->stages[this->stage_count++] = p_stage;
       memset(cf_arenax_resolve(this, 0), 0, sizeof(as_index));      

    ns->arena->stages[256]共有256个内存stage。

     最开始，只申请对第一个stages申请16M*sizeof(as_index)的内存空间。

3、as_partition_init(ns, pid);
     ->p->vp = as_index_tree_create(&ns->tree_shared, ns->arena);
     ->tree->arena = arena;      

    对partition进行初始化，树的内存都是共用一个arena，即ns->arena

while (cf_queue_pop(&g_gc_queue, &tree, CF_QUEUE_FOREVER) == CF_QUEUE_OK) {
        as_index_tree_destroy(tree);
     }