digoal
2021-08-23
PostgreSQL , 并行 distinct
This is implemented by introducing a two-phase DISTINCT. Phase 1 is
performed on parallel workers, rows are made distinct there either by
hashing or by sort/unique. The results from the parallel workers are
combined and the final distinct phase is performed serially to get rid of
any duplicate rows that appear due to combining rows for each of the
parallel workers.
引入了map reduce思路, 支持并行distinct. 如果能形成公共的api就更强了, 用户可以自定义操作.
《PostgreSQL 11 preview - 多阶段并行聚合array_agg, string_agg》
《HybridDB PostgreSQL "Sort、Group、distinct 聚合、JOIN" 不惧怕数据倾斜的黑科技和原理 - 多阶段聚合》
《PostgreSQL 10 自定义并行计算聚合函数的原理与实践 - (含array_agg合并多个数组为单个一元数组的例子)》
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