Re: [HACKERS] Block level parallel vacuum

On Fri, 10 Jan 2020 at 15:51, Sergei Kornilov <sk@zsrv.org> wrote:
>
> Hi
> Thank you for update! I looked again
>
> (vacuum_indexes_leader)
> +               /* Skip the indexes that can be processed by parallel workers */
> +               if (!skip_index)
> +                       continue;
>
> Does the variable name skip_index not confuse here? Maybe rename to something like can_parallel?
>

Again I looked into code and thought that somehow if we can add a
boolean flag(can_parallel)  in IndexBulkDeleteResult structure to
identify that this index is supporting parallel vacuum or not, then it
will be easy to skip those indexes and multiple time we will not call
skip_parallel_vacuum_index (from vacuum_indexes_leader and
parallel_vacuum_index)
We can have a linked list of non-parallel supported indexes, then
directly we can pass to vacuum_indexes_leader.

Ex: let suppose we have 5 indexes into a table.  If before launching
parallel workers, if we can add boolean flag(can_parallel)
IndexBulkDeleteResult structure to identify that this index is
supporting parallel vacuum or not.
Let index 1, 4 are not supporting parallel vacuum so we already have
info in a linked list that 1->4 are not supporting parallel vacuum, so
parallel_vacuum_index will process these indexes and rest will be
processed by parallel workers. If parallel worker found that
can_parallel is false, then it will skip that index.

As per my understanding, if we implement this, then we can avoid
multiple function calling of skip_parallel_vacuum_index and if there
is no index which can't  performe parallel vacuum, then we will not
call vacuum_indexes_leader as head of list pointing to null. (we can
save unnecessary calling of vacuum_indexes_leader)

Thoughts?

--
Thanks and Regards
Mahendra Singh Thalor
EnterpriseDB: http://www.enterprisedb.com