← Tuesday, October 13, 2026DatabasesDeep dive
Postgres TOAST compression can trigger when a value grows by one byte
The piece shows that a 2,000-byte value remains uncompressed while a 2,001-byte value is compressed to 26 bytes, then explains row-page limits and TOAST behavior. It also covers Postgres 19's shift to LZ4, useful context for storage and compression trade-offs.
- What
- TOAST compresses variable-length values when a Postgres row gets too large, and can move them out of the row if compression is insufficient.
- How
- A 2,000-character repeated value stays uncompressed, while 2,001 characters triggers LZ4 compression to 26 bytes.
- Why it matters
- Knowing the row-size trigger and compression behavior helps engineers reason about storage costs; Postgres 19 defaults to LZ4 when supported.
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