Re: [PoC] Reducing planning time when tables have many partitions

Hello Alena,

Thank you for your quick response, and I'm sorry for my delayed reply.

On Sun, Dec 17, 2023 at 12:41 AM Alena Rybakina
<lena(dot)ribackina(at)yandex(dot)ru> wrote:
> I thought about this earlier and was worried that the index links of the equivalence classes might not be referenced correctly for outer joins,
> so I decided to just overwrite them and reset the previous ones.

Thank you for pointing this out. I have investigated this problem and
found a potential bug place. The code quoted below modifies
RestrictInfo's clause_relids. Here, our indexes, namely
eclass_source_indexes and eclass_derive_indexes, are based on
clause_relids, so they should be adjusted after the modification.
However, my patch didn't do that, so it may have missed some
references. The same problem occurs in places other than the quoted
one.

=====
/*
* Walker function for replace_varno()
*/
static bool
replace_varno_walker(Node *node, ReplaceVarnoContext *ctx)
{
...
else if (IsA(node, RestrictInfo))
{
RestrictInfo *rinfo = (RestrictInfo *) node;
...

if (bms_is_member(ctx->from, rinfo->clause_relids))
{
replace_varno((Node *) rinfo->clause, ctx->from, ctx->to);
replace_varno((Node *) rinfo->orclause, ctx->from, ctx->to);
rinfo->clause_relids = replace_relid(rinfo->clause_relids,
ctx->from, ctx->to);
...
}
...
}
...
}
=====

I have attached a new version of the patch, v23, to fix this problem.
v23-0006 adds a helper function called update_clause_relids(). This
function modifies RestrictInfo->clause_relids while adjusting its
related indexes. I have also attached a sanity check patch
(sanity-check.txt) to this email. This sanity check patch verifies
that there are no missing references between RestrictInfos and our
indexes. I don't intend to commit this patch, but it helps find
potential bugs. v23 passes this sanity check, but the v21 you
submitted before does not. This means that the adjustment by
update_clause_relids() is needed to prevent missing references after
modifying clause_relids. I'd appreciate your letting me know if v23
doesn't solve your concern.

One of the things I don't think is good about my approach is that it
adds some complexity to the code. In my approach, all modifications to
clause_relids must be done through the update_clause_relids()
function, but enforcing this rule is not so easy. In this sense, my
patch may need to be simplified more.

> this is due to the fact that I explained before: we zeroed the values indicated by the indexes,
> then this check is not correct either - since the zeroed value indicated by the index is correct.
> That's why I removed this check.

Thank you for letting me know. I fixed this in v23-0005 to adjust the
indexes in update_eclasses(). With this change, the assertion check
will be correct.

--
Best regards,
Yuya Watari