On Sun, 1 Dec 2019 at 11:06, Sergei Kornilov <s...@zsrv.org> wrote: > > Hi > > > I think the advantage of the current approach is that once the parallel > > workers are launched, the leader can process indexes that don't support > > parallelism. So, both type of indexes can be processed at the same time. > > In lazy_parallel_vacuum_or_cleanup_indexes I see: > > /* > * Join as a parallel worker. The leader process alone does that in > * case where no workers launched. > */ > if (lps->leaderparticipates || lps->pcxt->nworkers_launched == 0) > vacuum_or_cleanup_indexes_worker(Irel, nindexes, stats, > lps->lvshared, > > vacrelstats->dead_tuples); > > /* > * Here, the indexes that had been skipped during parallel index > vacuuming > * are remaining. If there are such indexes the leader process does > vacuum > * or cleanup them one by one. > */ > vacuum_or_cleanup_skipped_indexes(vacrelstats, Irel, nindexes, stats, > > lps); > > So parallel leader will process parallel indexes first along with parallel > workers and skip non-parallel ones. Only after end of the index list parallel > leader will process non-parallel indexes one by one. In case of equal index > processing time parallel leader will process (count of parallel > indexes)/(nworkers+1) + all non-parallel, while parallel workers will process > (count of parallel indexes)/(nworkers+1). I am wrong here? >
I think I got your point. Your proposal is that it's more efficient if we make the leader process vacuum the index that can be processed only the leader process (i.e. indexes not supporting parallel index vacuum) while workers are processing indexes supporting parallel index vacuum, right? That way, we can process indexes in parallel as much as possible. So maybe we can call vacuum_or_cleanup_skipped_indexes first and then call vacuum_or_cleanup_indexes_worker. But I'm not sure that there are parallel-safe remaining indexes after the leader finished vacuum_or_cleanup_indexes_worker, as described on your proposal. Regards, -- Masahiko Sawada http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
