PostgreSQL 19 will change the default TOAST compression algorithm from pglz to lz4. TOAST handles out-of-line storage for oversized column values, and lz4 offers significantly faster compression and decompression with only a modest reduction in compression ratio (~7% less tight than pglz). The default stayed pglz through versions 14–18 because lz4 required an optional build dependency, but PostgreSQL 19 flips lz4 to an opt-out dependency and makes it the default when available. For users on versions 14–18, switching to lz4 is safe and recommended: existing data retains its original compression algorithm, new writes use the new setting, and no migration or rewrite is required. Switching existing data requires an explicit table rewrite.
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