哈希分区实现
学习 PostgreSQL 如何使用键的哈希值，将行均匀分布到固定数量的分区中；这种方式非常适合在没有自然范围的情况下平衡负载。
哈希分区实现 是 CoddyKit 上的免费 Advanced PostgreSQL: Indexing, Partitioning, Replication 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 Advanced PostgreSQL: Indexing, Partitioning, Replication 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Advanced PostgreSQL: Indexing, Partitioning, Replication 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。
When Range and List Do Not Fit
Range partitioning suits dates; list partitioning suits known categories. But what if you just want even distribution with no natural boundaries?
That is where hash partitioning shines.
What Is Hash Partitioning?
Hash partitioning applies a hash function to the partition key and assigns each row to a partition based on the remainder, spreading rows evenly.
Declaring the Parent Table
Create the parent table partitioned BY HASH on a key column.
CREATE TABLE events (
id BIGINT,
user_id BIGINT,
payload TEXT
) PARTITION BY HASH (user_id);Creating Partitions
Each partition declares a modulus and remainder. With modulus 4 you create four partitions, remainders 0 to 3.
CREATE TABLE events_0 PARTITION OF events FOR VALUES WITH (MODULUS 4, REMAINDER 0);The Full Set
You must create partitions covering every remainder, otherwise some rows have nowhere to go.
CREATE TABLE events_1 PARTITION OF events FOR VALUES WITH (MODULUS 4, REMAINDER 1);
CREATE TABLE events_2 PARTITION OF events FOR VALUES WITH (MODULUS 4, REMAINDER 2);
CREATE TABLE events_3 PARTITION OF events FOR VALUES WITH (MODULUS 4, REMAINDER 3);How Rows Get Routed
On insert, PostgreSQL hashes user_id, takes the remainder modulo 4, and stores the row in the matching partition automatically.
Even Distribution
Because hashing scatters values, partitions stay roughly equal in size, avoiding the hot-partition problem that range partitioning can suffer.
Choosing the Modulus
The modulus equals your number of partitions. Pick it up front, since changing partition count later requires redistributing data.
Indexes per Partition
Create indexes on the parent and PostgreSQL propagates them to all partitions, keeping lookups fast within each shard.
CREATE INDEX ON events (user_id);Hash vs Range vs List
- Range: ordered boundaries (dates, numbers)
- List: discrete known values (regions)
- Hash: even spread when no natural grouping exists
Limitations
Hash partitioning gives no partition pruning for range queries on the key, since values are scattered. It helps point lookups and write distribution, not range scans.
Quick Check
Test your hash partitioning knowledge.
Recap
Hash partitioning spreads rows evenly across a fixed number of partitions using MODULUS and REMAINDER on a hashed key.
It is ideal for balancing writes and point lookups when there is no natural range or list, but it cannot prune partitions for range queries on the key.
常见问题解答
「哈希分区实现」课时是免费的吗？
是的 — 「哈希分区实现」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 Advanced PostgreSQL: Indexing, Partitioning, Replication 课程的其余内容，请升级到 CoddyKit PRO。 Advanced PostgreSQL: Indexing, Partitioning, Replication 课程共包含 4 节课。
「哈希分区实现」这节课中我会学到什么？
学习 PostgreSQL 如何使用键的哈希值，将行均匀分布到固定数量的分区中；这种方式非常适合在没有自然范围的情况下平衡负载。 你通过在浏览器中直接运行的动手代码来练习 Advanced PostgreSQL: Indexing, Partitioning, Replication，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 Advanced PostgreSQL: Indexing, Partitioning, Replication 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Advanced PostgreSQL: Indexing, Partitioning, Replication 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。
「哈希分区实现」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 Advanced PostgreSQL: Indexing, Partitioning, Replication 课中编写并运行代码吗？
能。每节 Advanced PostgreSQL: Indexing, Partitioning, Replication 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。