Re: parallel vacuum comments

On Tue, Nov 2, 2021 at 2:46 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> Anyway, I'll write a patch accordingly.

While writing a patch for these comments, I found another bug in
parallel_processing_is_safe():

/*
 * Returns false, if the given index can't participate in parallel index
 * vacuum or parallel index cleanup
 */
static bool
parallel_processing_is_safe(Relation indrel, LVShared *lvshared)
{
    uint8       vacoptions = indrel->rd_indam->amparallelvacuumoptions;

    /* first_time must be true only if for_cleanup is true */
    Assert(lvshared->for_cleanup || !lvshared->first_time);

    if (lvshared->for_cleanup)
    {
        /* Skip, if the index does not support parallel cleanup */
        if (((vacoptions & VACUUM_OPTION_PARALLEL_CLEANUP) == 0) &&
            ((vacoptions & VACUUM_OPTION_PARALLEL_COND_CLEANUP) == 0))
            return true;

It returns true in the above condition but it should return false
since the index doesn't support parallel index cleanup at all. It
seems that this bug was introduced by commit b4af70cb21 (therefore
exists only in PG14) which flipped the return values of this function
but missed one place. The index AMs that don't support parallel index
cleanup at all are affected by this bug. Among the supported index AM
in the core, hash indexes are affected but since they just return the
number of blocks during vacuumcleanup it would not become a serious
consequence.

I've attached a patch to fix it.

Regards,

-- 
Masahiko Sawada
EDB:  https://www.enterprisedb.com/