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hide-storage-cache-related-content #2521

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Jan 30, 2023
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7 changes: 7 additions & 0 deletions docs-2.0/1.introduction/3.nebula-graph-architecture/4.storage-service.md
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Expand Up @@ -247,10 +247,17 @@ leader 切换对于负载均衡至关重要，当把某个分片从一台机器

为了避免脑裂，当一个 Raft group 的成员发生变化时，需要有一个中间状态，该状态下新旧 group 的多数派需要有重叠的部分，这样就防止了新的 group 或旧的 group 单方面做出决定。为了更加简化，Diego Ongaro 在自己的博士论文中提出每次只增减一个 peer 的方式，以保证新旧 group 的多数派总是有重叠。NebulaGraph 也采用了这个方式，只不过增加成员和移除成员的实现有所区别。具体实现方式请参见 Raft Part class 里 addPeer/removePeer 的实现。

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{{ent.ent_begin}}
## 缓存

由于 RocksDB 本身的缓存管理存在限制，无法按需缓存点或边，所以 NebulaGraph 自行实现了 Storage 缓存管理，可以更自由地设置缓存大小、内容等。详情参见 [storage cache 配置](../../5.configurations-and-logs/1.configurations/4.storage-config.md)。

用户可以通过 cURL 命令`curl "http://[storaged IP]:[http port]/cache?stats"`查询缓存数据信息。

{{ent.ent_end}} -->

## 与 HDFS 的区别

Storage 服务基于 Raft 协议实现的分布式架构，与 HDFS 的分布式架构有一些区别。例如：
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4 changes: 3 additions & 1 deletion docs-2.0/5.configurations-and-logs/1.configurations/4.storage-config.md
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Expand Up @@ -174,6 +174,8 @@ rocksdb options 配置的格式为`{"<option_name>":"<option_value>"}`，多个

{{ ent.ent_begin }}

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## storage cache 配置

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Expand All @@ -190,7 +192,7 @@ rocksdb options 配置的格式为`{"<option_name>":"<option_value>"}`，多个
| `vertex_item_ttl` | `300` | 点缓存条目的有效时间。单位：秒。 |
| `enable_negative_pool` | `false`| 是否添加消极缓存池（消极缓存池表示 Key 不存在于数据库中的数据缓存池）。仅当`enable_storage_cache`为`true`时有效。 |
| `negative_pool_capacity` | `50` | 消极缓存池的大小。 单位：兆字节。 |
| `negative_item_ttl` | `300` | 消极缓存条目的有效时间。单位：秒。 |
| `negative_item_ttl` | `300` | 消极缓存条目的有效时间。单位：秒。 | -->

## Black box 配置

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