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PostgreSQL Performance & Query Optimization · 课时

设计主键与代理键

学习自然键、顺序代理键和 UUID 之间的选择如何影响索引大小、插入吞吐量和整体查询性能

设计主键与代理键 是 CoddyKit 上的免费 PostgreSQL Performance & Query Optimization 课时。 这是第 4 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 PostgreSQL Performance & Query Optimization 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 PostgreSQL Performance & Query Optimization 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Natural vs Surrogate Keys

A natural key is a real-world attribute (e.g. email). A surrogate key is a meaningless generated value (e.g. an integer id). Surrogate keys stay stable even when business data changes.

Why Key Choice Affects Performance

The primary key is referenced by every foreign key and many indexes. A wide key bloats all of those structures, increasing disk usage and cache pressure. Narrow keys keep indexes small and fast.

Sequential Integer Keys

The classic choice is a monotonically increasing integer. New rows append to the end of the B-tree, minimizing page splits and keeping inserts fast.

CREATE TABLE orders (
  id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
  total NUMERIC
);

IDENTITY vs serial

Prefer the SQL-standard GENERATED ALWAYS AS IDENTITY over the older serial pseudo-type. It is cleaner and avoids ownership quirks with the underlying sequence.

The UUID Temptation

UUIDs are great for distributed systems because clients can generate them. But random UUIDs (v4) scatter inserts all over the index, causing page splits and poor cache locality.

CREATE TABLE events (
  id UUID DEFAULT gen_random_uuid() PRIMARY KEY,
  payload JSONB
);

Time-Ordered UUIDs

If you need UUIDs, prefer a time-ordered variant (UUIDv7) so values increase roughly with time. This restores the append-friendly behavior of sequential keys while keeping global uniqueness.

Key Width Matters

A BIGINT is 8 bytes; a UUID is 16 bytes. Every secondary index stores the primary key, so wider keys multiply storage across all of them. Measure the impact.

SELECT pg_size_pretty(pg_relation_size('orders_pkey'));

Composite Primary Keys

Sometimes the natural key spans two columns, such as (order_id, line_no) in a detail table. Keep composite keys narrow and put the most selective column first.

CREATE TABLE order_lines (
  order_id BIGINT,
  line_no  INT,
  PRIMARY KEY (order_id, line_no)
);

Foreign Keys Inherit the Cost

Every child row stores a copy of the parent key. A 16-byte UUID parent key makes a million-row child table 8 MB larger than an 8-byte integer would. Multiply by every referencing table.

Choosing in Practice

Guidelines:

  • Default to BIGINT IDENTITY for single-database apps
  • Use time-ordered UUIDs when clients must generate ids or you shard
  • Avoid random v4 UUIDs as primary keys on hot insert paths
  • Keep composite natural keys short

Indexing the Foreign Key Side

Whatever key you pick, always index the child's foreign key column. Without it, deleting or updating a parent forces a full scan of the child table to check references.

CREATE INDEX idx_order_lines_order
ON order_lines (order_id);

Quick Check

Test your key-design knowledge.

Recap

You learned key design for performance:

  • Surrogate keys stay stable; natural keys can change
  • Narrow keys shrink every index and foreign key
  • Sequential BIGINT IDENTITY inserts are cheap
  • Random v4 UUIDs scatter inserts; prefer time-ordered UUIDs
  • Keep composite keys short and selective-first

常见问题解答

「设计主键与代理键」课时是免费的吗？

是的 — 「设计主键与代理键」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 PostgreSQL Performance & Query Optimization 课程的其余内容，请升级到 CoddyKit PRO。 PostgreSQL Performance & Query Optimization 课程共包含 4 节课。

「设计主键与代理键」这节课中我会学到什么？

学习自然键、顺序代理键和 UUID 之间的选择如何影响索引大小、插入吞吐量和整体查询性能 你通过在浏览器中直接运行的动手代码来练习 PostgreSQL Performance & Query Optimization，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 PostgreSQL Performance & Query Optimization 需要有经验吗？

无需任何先前经验。CoddyKit 上的 PostgreSQL Performance & Query Optimization 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 4 节课，共 4 节。

「设计主键与代理键」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 PostgreSQL Performance & Query Optimization 课中编写并运行代码吗？

能。每节 PostgreSQL Performance & Query Optimization 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

此课程中的所有课时

  1. 规范化与反规范化的权衡
  2. 选择合适的数据类型
  3. 对大型表进行分区
  4. 设计主键与代理键
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