> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-postgresql-tls-support.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# map_serialization_version_* MergeTree 表设置

> ClickHouse 中 map_serialization_version_* 自动生成分组下的 MergeTree 表设置。

export const VersionHistory = ({rows = []}) => {
  if (rows.length === 0) {
    return null;
  }
  const headers = ["版本", "默认值", "注释"];
  const border = "1px solid rgba(128, 128, 128, 0.3)";
  const cell = {
    border,
    padding: "0.25rem 0.5rem",
    textAlign: "start",
    verticalAlign: "top"
  };
  return <details className="not-prose" style={{
    border,
    borderRadius: "0.5rem",
    margin: "0.5rem 0",
    padding: "0.5rem 0.75rem",
    fontSize: "0.8125rem",
    lineHeight: "1.125rem"
  }}>
      <summary style={{
    cursor: "pointer",
    fontWeight: 600,
    opacity: 0.72
  }}>
        版本历史
      </summary>
      <table style={{
    borderCollapse: "collapse",
    width: "100%",
    margin: "0.5rem 0 0"
  }}>
        <thead>
          <tr>
            {headers.map(header => <th key={header} style={{
    ...cell,
    fontWeight: 600,
    opacity: 0.72
  }}>
                {header}
              </th>)}
          </tr>
        </thead>
        <tbody>
          {rows.map((row, row_index) => <tr key={row.id ?? row_index}>
              {(row.items ?? []).map((item, item_index) => <td key={item_index} style={{
    ...cell,
    overflowWrap: "anywhere"
  }}>
                  {item?.label}
                </td>)}
            </tr>)}
        </tbody>
      </table>
    </details>;
};

export const SettingsInfoBlock = ({type, default_value, changeable_without_restart}) => {
  return <div className="not-prose" style={{
    display: "flex",
    flexWrap: "wrap",
    alignItems: "baseline",
    columnGap: "0.5rem",
    rowGap: "0.125rem",
    margin: "0.375rem 0",
    fontSize: "0.8125rem",
    lineHeight: "1.125rem"
  }}>
      <div style={{
    fontWeight: 600,
    opacity: 0.72
  }}>类型</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{type}</div>
      <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>默认值</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{default_value}</div>
      {changeable_without_restart && <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>
          无需重启即可更改
        </div>}
      {changeable_without_restart && <div style={{
    overflowWrap: "anywhere"
  }}>
          {changeable_without_restart}
        </div>}
    </div>;
};

这些设置可在 [system.merge\_tree\_settings](/zh/reference/system-tables/merge_tree_settings) 中查看，且由 ClickHouse 源代码自动生成。

<div id="map_serialization_version">
  ## map\_serialization\_version
</div>

<SettingsInfoBlock type="MergeTreeMapSerializationVersion" default_value="basic" />

控制 `Map` 列使用的序列化方法。

可能的值：

* basic — 对 `Map` 使用标准序列化。
* with\_buckets — 在序列化过程中将键拆分到桶中。使用桶可提升从 Map 中读取单个键的效率。

`with_buckets` 序列化中的桶数量由 [max\_buckets\_in\_map](/zh/reference/settings/merge-tree-settings/max#max_buckets_in_map) 和 [map\_buckets\_strategy](/zh/reference/settings/merge-tree-settings/map-buckets#map_buckets_strategy) 决定。

<div id="map_serialization_version_for_zero_level_parts">
  ## map\_serialization\_version\_for\_zero\_level\_parts
</div>

<SettingsInfoBlock type="MergeTreeMapSerializationVersion" default_value="basic" />

此设置允许为插入时创建的零级 parts 的
`Map` 列指定不同的序列化版本。
如果希望在插入时避免性能下降，可以对零级 parts 保持使用 `basic`
序列化，同时对合并后的 parts 使用 `with_buckets`。