On Tue, 12 Sept 2023 at 02:27, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > > David Rowley <dgrowleyml@xxxxxxxxx> writes: > > I'm not sure if you're asking for help here because you need planning > > to be faster than it currently is, or if it's because you believe that > > planning should always be faster than execution. If you think the > > latter, then you're mistaken. > > Yeah. I don't see anything particularly troubling here. Taking > circa three-quarters of a millisecond (on typical current hardware) > to plan a four-way join on large tables is not unreasonable. I took a few minutes to reverse engineer the tables in question (with assistance from an AI bot) and ran the query in question. Unsurprisingly, I also see planning as slower than execution, but with a ratio of about planning being 12x slower than execution vs the reported ~18x. Planning Time: 0.581 ms Execution Time: 0.048 ms Nothing alarming in perf top of executing the query in pgbench with -M simple. I think this confirms the problem is just with expectations. 5.09% postgres [.] AllocSetAlloc 2.99% postgres [.] SearchCatCacheInternal 2.52% postgres [.] palloc 2.38% postgres [.] expression_tree_walker_impl 1.82% postgres [.] add_path_precheck 1.78% postgres [.] add_path 1.73% postgres [.] MemoryContextAllocZeroAligned 1.63% postgres [.] base_yyparse 1.61% postgres [.] CatalogCacheComputeHashValue 1.38% postgres [.] try_nestloop_path 1.36% postgres [.] stack_is_too_deep 1.33% postgres [.] add_paths_to_joinrel 1.19% postgres [.] core_yylex 1.18% postgres [.] lappend 1.15% postgres [.] initial_cost_nestloop 1.13% postgres [.] hash_search_with_hash_value 1.01% postgres [.] palloc0 0.95% postgres [.] get_memoize_path 0.90% postgres [.] equal 0.88% postgres [.] get_eclass_for_sort_expr 0.81% postgres [.] compare_pathkeys 0.80% postgres [.] bms_is_subset 0.77% postgres [.] ResourceArrayRemove 0.77% postgres [.] check_stack_depth 0.77% libc.so.6 [.] __memmove_avx_unaligned_erms 0.74% libc.so.6 [.] __memset_avx2_unaligned 0.73% postgres [.] AllocSetFree 0.71% postgres [.] final_cost_nestloop 0.69% postgres [.] compare_path_costs_fuzzily 0.68% postgres [.] initial_cost_mergejoin 0.64% libc.so.6 [.] __memset_avx2_unaligned_erms 0.61% postgres [.] create_nestloop_path 0.61% postgres [.] examine_variable 0.59% postgres [.] hash_bytes 0.56% postgres [.] truncate_useless_pathkeys 0.56% postgres [.] bms_overlap David
