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Planet PostgreSQL0 Hot0 comments5 min read
All Your GUCs in a Row: max_index_keys
A deep dive into PostgreSQL's max_index_keys parameter reveals it has counted more than just key columns since INCLUDE columns arrived in version 11, capping any index (B-tree, GiST, GIN, BRIN, PRIMARY KEY, UNIQUE, EXCLUDE, foreign keys) at 32 total columns. The value has been fixed at 32 since PostgreSQL 7.3 (2002) because it's baked into the on-disk tuple format: a null bitmap in every index tuple is sized to INDEX_MAX_KEYS regardless of actual column count, and the value is recorded in pg_control and checked at startup, making it unraisable without recompiling, rebuilding every C extension, and a dump/restore. In practice the byte-size limit on B-tree tuples (a third of an 8kB page) is hit before the column limit, except when INCLUDE is misused to create an index covering every column of a wide table.
Source: https://postgr.es/p/9uv. 8 Sync News only summarizes and links out; content copyright belongs to the authors and original sources.
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