PostgreSQL 13中对vacuum的改进：Allow vacuum command to process indexes in parallel. >This feature allows the vacuum to leverage multiple CPUs in order to process indexes. This enables us to perform index vacuuming and index cleanup with background workers. This adds a PARALLEL option to VACUUM command where the user can specify the number of workers that can be used to perform the command which is limited by the number of indexes on a table. Specifying zero as a number of workers will disable parallelism. This option can't be used with the FULL option. Each index is processed by at most one vacuum process. Therefore parallel vacuum can be used when the table has at least two indexes. The parallel degree is either specified by the user or determined based on the number of indexes that the table has, and further limited by max_parallel_maintenance_workers. The index can participate in parallel vacuum iff it's size is greater than min_parallel_index_scan_size. 该新特性允许vacuum使用多个CPU来清理索引， 使用多个后台worker执行索引整理（vacuuming）和清理（cleanup）。 在vacuum命令中增加了PARALLE选项来指定worker的数量，0表示禁用并行，但该选项不能与FULL选项一起使用。 注意：仍然选择使用多进程的方式而不是在worker进程中使用多线程的方式进行vacuuming。 >Author: Masahiko Sawada and Amit Kapila Reviewed-by: Dilip Kumar, Amit Kapila, Robert Haas, Tomas Vondra, Mahendra Singh and Sergei Kornilov Tested-by: Mahendra Singh and Prabhat Sahu **参考资料** [Allow vacuum command to process indexes in parallel](https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=40d964ec997f64227bc0ff5e058dc4a5770a70a9)