{"Entry":{"collection":"guc","key":"geqo_generations","name":"geqo_generations","aliases":[],"metadata":{"baseline":true,"boot_human":"Not specified","boot_val":null,"category":"Query Tuning / Genetic Query Optimizer","category_zh":"","changed_in":["18"],"changes":[{"documentation_changed":true,"fields":{},"from":"7.4","status":"changed","to":"8.0"},{"documentation_changed":true,"fields":{},"from":"8.3","status":"changed","to":"8.4"},{"documentation_changed":false,"fields":{"extra_desc":{"from":"Zero selects a suitable default value.","to":"0 means use a suitable default value."}},"from":"17","status":"changed","to":"18"}],"content_hash":"869556a35e2952f07884f5ba91fb43a721d3286aba51321e37c2e3ccba4dec7f","context":"","default_changed_in":[],"default_history":[{"from":"9.0","to":"19","value":"0"}],"editorial":{"advice":{"olap":"For recurring many-table reports, test geqo_generations with multiple geqo_seed values and compare planning plus execution time. A single lucky seed is not a stable production policy.","oltp":"Keep geqo_generations at its upstream default unless planning time for many-way joins is measured as a problem. Prefer simplifying generated SQL or fixing join estimates before expanding a randomized search budget globally.","small":"Avoid increasing geqo_generations in ways that consume disproportionate planning CPU on a small host. The default adaptive values are safer than copying a large-system GEQO budget."},"mechanism":["It sets the number of evolutionary iterations; zero derives a value from the selected pool size.","GEQO trades bounded planning time for a heuristic search that can miss the best join order. It still costs scan and join paths with the ordinary planner cost model after constructing candidates.","The setting is read during planning, and GEQO's randomized search means plan quality can vary with seed and search budget. Collapse limits can change the number of relations exposed to the join search and therefore whether the threshold is crossed. Its user context permits session- or transaction-local changes; newly performed or newly planned work sees the value."],"pitfalls":["Judging plan quality from one randomized GEQO run.","Changing a GEQO knob without accounting for geqo_threshold and collapse limits.","Spending much more planning CPU for a marginal or unstable execution-time gain.","Assuming GEQO guarantees the globally best join order."],"references":[{"title":"PostgreSQL 19 Beta 4: geqo_generations","url":"https://www.postgresql.org/docs/19/runtime-config-query.html#GUC-GEQO-GENERATIONS"},{"title":"PostgreSQL 19 release notes","url":"https://www.postgresql.org/docs/19/release-19.html"}],"related":["geqo","geqo_pool_size","geqo_effort","geqo_seed","geqo_selection_bias"],"summary":"geqo_generations — GEQO: number of iterations of the algorithm. Observed in PG9.0–19 Beta 4; its last measured boot default is 0 in PG19 Beta 4, with user context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA."},"enumvals":[],"first_version":"7.4","group":"Query Tuning","group_slug":"query","imported_at":"2026-09-27T17:57:31.312053+08:00","intro_commit":{},"key":"geqo_generations","last_version":"20","max_val":"","min_val":"","name":"geqo_generations","position":155,"present_in":["7.4","8.0","8.1","8.2","8.3","8.4","9.0","9.1","9.2","9.3","9.4","9.5","9.6","10","11","12","13","14","15","16","17","18","19","20"],"short_desc":"Controls the number of generations used by GEQO, that is the number of iterations of the algorithm.","short_desc_zh":"","source_rev":"english-manuals:de36c19a7a0407a5800e3abd7e08c922d84e71e11428331a2ed000f3bb4df54c","unit":"","vartype":"integer"}},"Definition":{"Collection":"guc","Key":"geqo_generations","SourceDatabase":"center","Version":"18","SourceTable":"guc","SourceKey":"geqo_generations","SourceRevision":"english-manuals:de36c19a7a0407a5800e3abd7e08c922d84e71e11428331a2ed000f3bb4df54c","Facts":{"boot_val":"0","category":"Query Tuning / Genetic Query Optimizer","context":"user","description":"Controls the number of generations used by GEQO, that is the number of iterations of the algorithm. It must be at least one, and useful values are in the same range as the pool size. If it is set to zero (the default setting) then a suitable value is chosen based on geqo_pool_size.","doc":{"anchor":"GUC-GEQO-GENERATIONS","file":"runtime-config-query.html","lang":"en","sha256":"33456ca7ef52bf28e93e34b932a411db7a1b95800179add2cf867dc6ec9144bc","slug":"18"},"documented":true,"enumvals":null,"extra_desc":"0 means use a suitable default value.","lang":"en","max_val":"2147483647","metadata_version":"18","min_val":"0","name":"geqo_generations","short_desc":"GEQO: number of iterations of the algorithm.","source":"pg-settings-source-snapshot","unit":null,"vartype":"integer"},"ManualEvidence":{"doc":{"anchor":"GUC-GEQO-GENERATIONS","file":"runtime-config-query.html","lang":"en","sha256":"33456ca7ef52bf28e93e34b932a411db7a1b95800179add2cf867dc6ec9144bc","slug":"18"}},"MeasuredEvidence":{"metadata_version":"18"}},"Text":{"Collection":"guc","Key":"geqo_generations","SourceDatabase":"center","Version":"18","Locale":"en","Title":"geqo_generations","Summary":"Controls the number of generations used by GEQO, that is the number of iterations of the algorithm. It must be at least one, and useful values are in the same range as the pool size. If it is set to zero (the default setting) then a suitable value is chosen based on geqo_pool_size.","BodyHTML":"\u003cp\u003eControls the number of generations used by GEQO, that is the number of iterations of the algorithm. It must be at least one, and useful values are in the same range as the pool size. If it is set to zero (the default setting) then a suitable value is chosen based on geqo_pool_size.\u003c/p\u003e","SourceRevision":"english-manuals:de36c19a7a0407a5800e3abd7e08c922d84e71e11428331a2ed000f3bb4df54c","ContentHash":"b579b3c4e0e3c5bd6d9e52456bd7c81b25d310328a6e3c3232d24e0e1c548021","Payload":{"description":"Controls the number of generations used by GEQO, that is the number of iterations of the algorithm. It must be at least one, and useful values are in the same range as the pool size. If it is set to zero (the default setting) then a suitable value is chosen based on geqo_pool_size."}},"RequestedLocale":"zh-Hans","Fallback":true,"Versions":["10","11","12","13","14","15","16","17","18","19","20","7.4","8.0","8.1","8.2","8.3","8.4","9.0","9.1","9.2","9.3","9.4","9.5","9.6"],"Locales":["en"],"Signatures":null,"Spellings":null,"SQLState":null,"Evidence":null}