# 备份策略

> 设计并配置备份策略：备份频率决定恢复速度，保留策略决定恢复窗口与空间占用，两张推演图帮您做出量化决策。

---

LLMS index: [llms.txt](/llms.txt)

---

备份策略要回答三个问题：**何时** 备份（调度计划）、**何处** 存放（[**备份仓库**](/docs/pgsql/backup/repository)）、
**保留多久**（保留策略）。本页给出两套久经考验的预设策略及其量化推演 ——
背后的权衡逻辑请参阅概念层文档 [**策略权衡**](/docs/concept/pitr/tradeoff/)。

备份频率与恢复速度直接相关：恢复时需要从最近的基础备份开始重放 WAL 日志到目标时间点，
备份越频繁，需要重放的 WAL 越少，恢复越快；而保留策略与仓库空间直接相关：窗口越长，占用空间越大。


--------

## 每日全量备份

对于生产数据库，建议从最简单的每日全量备份策略开始。Pigsty 随附的标准 `pigsty.yml` 集群示例采用这一策略，
配合默认的 `local` 本地仓库（保留最近 2 个全量备份）使用：

```yaml title="每天凌晨1点全量备份，本地仓库保留2份"
pg_crontab: [ '00 01 * * * /pg/bin/pg-backup full' ]
pgbackrest_method: local          # 选择备份仓库方法：`local`、`minio` 或其他自定义仓库
pgbackrest_repo:                  # pgbackrest 仓库配置: https://pgbackrest.org/configuration.html#section-repository
  local:                          # 使用本地 POSIX 文件系统的默认 pgbackrest 仓库
    path: /pg/backup              # 本地备份目录，默认为 `/pg/backup`
    retention_full_type: count    # 按数量保留全量备份
    retention_full: 2             # 使用本地文件系统仓库时，保留2个，最多3个全量备份
```

假设您的数据库大小为 100GB，每天写入 10GB 数据，备份耗时 1 小时。
下图将「恢复窗口」与「存储空间占用」合并到同一时间轴（`0~108h`）上推演该策略的稳态行为：
恢复窗口在 **24～48 小时** 之间循环，备份占用约为 2 个全量备份加上 1～2 天的 WAL 归档。
在实践中，您需要准备至少 **3～5 倍** 数据库大小的备份磁盘，才能从容使用该默认策略。


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--------

## 全量 + 增量备份

如果使用 Silo / S3 作为集中式备份仓库，存储空间不再受本地磁盘限制，
此时可以用「周全量 + 每日增量」配合两周保留策略，换取更长的恢复窗口：

```yaml title="周一全量备份，其余日期增量备份，保留14天"
pg_crontab:  # 周一凌晨1点全量备份，其余每日增量备份
  - '00 01 * * 1           /pg/bin/pg-backup full'
  - '00 01 * * 2,3,4,5,6,7 /pg/bin/pg-backup'
pgbackrest_method: minio
pgbackrest_repo:                  # pgbackrest 仓库配置: https://pgbackrest.org/configuration.html#section-repository
  minio:                          # 可选的 minio 仓库
    type: s3                      # minio 兼容 S3 协议
    s3_endpoint: sss.pigsty       # minio 端点域名，默认为 `sss.pigsty`
    s3_region: us-east-1          # minio 区域，默认 us-east-1，对 minio 无实际意义
    s3_bucket: pgsql              # minio 桶名，默认为 `pgsql`
    s3_key: pgbackrest            # pgbackrest 的 minio 用户访问密钥
    s3_key_secret: S3User.Backup  # 对象存储用户密钥
    s3_uri_style: path            # minio 使用路径风格 URI 而非主机风格
    path: /pgbackrest             # minio 备份路径，默认为 `/pgbackrest`
    storage_port: 9000            # minio 端口，默认 9000
    storage_ca_file: /etc/pki/ca.crt  # minio CA 证书路径，默认 `/etc/pki/ca.crt`
    block: y                      # 启用块级增量备份
    bundle: y                     # 将小文件打包成单个文件
    bundle_limit: 20MiB           # 文件包大小限制，对象存储建议 20MiB
    bundle_size: 128MiB           # 文件包目标大小，对象存储建议 128MiB
    cipher_type: aes-256-cbc      # 为远程备份仓库启用 AES 加密
    cipher_pass: pgBackRest       # 仓库加密密码
    retention_full_type: time     # 按时间保留全量备份
    retention_full: 14            # 按时间保留 14 天
```

同样假设数据库 100GB、每日增量与 WAL 均按 10GB 粗估，下图推演 30 天内恢复窗口与存储占用的变化：
`retention_full_type: time` 会确保至少留下一份年龄达到 14 天的全量备份，周全备时恢复窗口在 **14～21 天** 之间循环。
按这组未压缩假设，稳态占用约为 560～690GB，新全量完成、旧链过期前的瞬时峰值约为 790GB；
实际占用取决于 WAL 量、块级增量命中率与 zstd 压缩率。


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--------

## 空间规划

两套策略的空间需求可以按以下经验公式粗估（实际占用受压缩与块级增量影响，通常更低）：

| 策略                          | 恢复窗口     | 空间粗估                             | 建议预留            |
|:----------------------------|:---------|:---------------------------------|:----------------|
| 每日全量，保留 2 份（local）          | 24～48 小时 | 2 × 全量 + 1～2 天 WAL               | 数据库大小的 3～5 倍    |
| 周全量 + 日增量，按时间保留 14 天（minio） | 14～21 天  | 3 × 全量 + 12～18 份增量 + 14～21 天 WAL | 按实测压缩率与 WAL 量规划 |
{.full-width}

注意 **瞬时峰值**：新的全量备份成功完成后，旧备份才会参与过期计算，因此仓库会短暂多出一份全量备份，
同时保留尚未清理的旧备份链与 WAL。空间规划必须覆盖这个峰值而非只看清理后的稳态。

WAL 归档的增长与写入负载成正比。批量导数、`VACUUM FULL`、大规模 `UPDATE` 都会瞬间产生大量 WAL，
如果备份仓库空间紧张，请在此类操作前后关注仓库水位（[**监控指标**](/docs/pgbackrest/metric) 开箱即用）。


--------

## 应用策略变更

备份策略的三类变更，分别用对应的剧本任务应用：

```bash
./pgsql.yml -t pg_crontab -l pg-meta    # 变更调度计划（pg_crontab）后：更新 crontab
./pgsql.yml -t pg_backup  -l pg-meta    # 变更仓库定义（pgbackrest_repo / pgbackrest_method）后：重新渲染配置并初始化 stanza
pg-backup full                          # 切换仓库后：立即执行一次全量备份，建立新仓库中的恢复起点
```

注意：切换 [**`pgbackrest_method`**](/docs/pgsql/param#pgbackrest_method) 到新仓库后，旧仓库中的备份不会自动迁移；
在新仓库完成首次全量备份之前，恢复窗口存在缺口。