PostgreSQL 12为explain命令提供了settings选项,可查看影响执行计划的设置修改. 影响PG执行计划的参数包括： >enable_seqscan, enable_indexscan enable_index only scan, enable_bitmapscan; temp_buffers, work_mem; max_parallel_workers_per_gather, max_parallel_workers, enable_gathermerge; effective_cache_size; min_parallel_table_scan_size, min_parallel_index_scan_size; enable_parallel_append, enable_parallel_hash, enable_partition_pruning; enable_nestloop, enable_mergejoin, enable_hashjoin; enable_tidscan; enable_sort; enable_hashagg; enable_material; enable_partitionwise_join; enable_partitionwise_aggregate; geqo; optimize_bounded_sort; parallel_leader_participation; jit; from_collapse_limit; join_collapse_limit; geqo_threshold; geqo_effort; geqo_pool_size; geqo_generations; effective_io_concurrency; ``` [local:/data/run/pg12]:5120 pg12@testdb=# explain (format text,settings on) select * from t_mvcc; QUERY PLAN ---------------------------------------------------------- Seq Scan on t_mvcc (cost=0.00..35.50 rows=2550 width=4) (1 row) [local:/data/run/pg12]:5120 pg12@testdb=# set enable_seqscan=off; SET [local:/data/run/pg12]:5120 pg12@testdb=# explain (format text,settings on) select * from t_mvcc; QUERY PLAN ----------------------------------------------------------------------------- Seq Scan on t_mvcc (cost=10000000000.00..10000000035.50 rows=2550 width=4) Settings: enable_seqscan = 'off' (2 rows) [local:/data/run/pg12]:5120 pg12@testdb=# ``` 值得一提的是，设置enable_XXXscan=off并不是真的禁用而是把该路径的成本设置为一个很大的值（10000000000）。 **参考资料** [Waiting for PostgreSQL 12 – Add SETTINGS option to EXPLAIN, to print modified settings](https://www.depesz.com/2019/04/30/waiting-for-postgresql-12-add-settings-option-to-explain-to-print-modified-settings/) [PostgreSQL 12 EXPLAIN SETTINGS](https://fluca1978.github.io/2019/12/05/Explain_settings.html) [Add SETTINGS option to EXPLAIN, to print modified settings.](https://github.com/postgres/postgres/commit/ea569d64ac7174d3fe657e3e682d11053ecf1866)