If you are using standard uuid_generate_v4() or gen_random_uuid() as a Primary Key in PostgreSQL, you have likely architected a performance time bomb. It usually detonates when the table size exceeds available RAM. In the early days of an application, with 100,000 rows, your entire index fits in shared_buffers (Postgres's page cache). Writes are fast because they are effectively in-memory operations. However, as you scale to 50M+ rows, insert latency stops being linear and hits a "random I/O cliff." This post analyzes why the B-Tree fails with random inputs and how to solve it using UUIDv7 (RFC 9562). The Root Cause: B-Tree Mechanics and Random I/O PostgreSQL uses B-Tree indexes for Primary Keys by default. B-Trees are balanced tree structures optimized for sorted data. They strive to keep the tree balanced to ensure O(log n) lookup times. The Problem with Randomness (UUIDv4) A UUIDv4 is 128 bits of pseudo-randomness. When you i...
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