> That code could be modified to swap the tuplestores and do a > tuplestore_clear() instead of tuplestore_end() followed by > tuplestore_begin_heap(). > > It's likely worthwhile from a performance point of view. Here's a > small test as an example: > > master: > postgres=# with recursive cte (a) as (select 1 union all select > cte.a+1 from cte where cte.a+1 <= 1000000) select count(*) from cte; > Time: 219.023 ms > Time: 218.828 ms > Time: 219.093 ms > > with attached patched: > postgres=# with recursive cte (a) as (select 1 union all select > cte.a+1 from cte where cte.a+1 <= 1000000) select count(*) from cte; > Time: 169.734 ms > Time: 164.841 ms > Time: 169.168 ms
Impressive result. I also ran your query with count 1000. without the patch: Time: 3.655 ms Time: 4.123 ms Time: 2.163 ms wit the patch: Time: 3.641 ms Time: 2.356 ms Time: 2.347 ms It seems with the patch the performance is slightly better or almost same. I think the patch improves the performance without sacrificing the smaller iteration case. Best reagards, -- Tatsuo Ishii SRA OSS K.K. English: http://www.sraoss.co.jp/index_en/ Japanese:http://www.sraoss.co.jp
