Re: [HACKERS] path toward faster partition pruning

On 10 January 2018 at 17:18, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
> Basically, the changes to add_paths_to_append_rel() are causing
> duplication in partition_rels.
>
> A test case is:
>
> create table part (a int, b int) partition by list(a);
> create table part1 partition of part for values in(1) partition by list (b);
> create table part2 partition of part1 for values in(1);
>
> select * from part;
>
> partition_rels ends up with 3 items in the list, but there's only 2
> partitions here. The reason for this is that, since planning here is
> recursively calling add_paths_to_append_rel, the list for part ends up
> with itself and part1 in it, then since part1's list already contains
> itself, per set_append_rel_size's "rel->live_partitioned_rels =
> list_make1_int(rti);", then part1 ends up in the list twice.
>
> It would be nicer if you could use a RelIds for this, but you'd also
> need some way to store the target partition relation since
> nodeModifyTable.c does:
>
> /* The root table RT index is at the head of the partitioned_rels list */
> if (node->partitioned_rels)
> {
> Index root_rti;
> Oid root_oid;
>
> root_rti = linitial_int(node->partitioned_rels);
> root_oid = getrelid(root_rti, estate->es_range_table);
> rel = heap_open(root_oid, NoLock); /* locked by InitPlan */
> }
>
> You could also fix it by instead of doing:
>
> /*
> * Accumulate the live partitioned children of this child, if it's
> * itself partitioned rel.
> */
> if (childrel->part_scheme)
> partitioned_rels = list_concat(partitioned_rels,
> childrel->live_partitioned_rels);
>
> do something along the lines of:
>
> if (childrel->part_scheme)
> {
> ListCell *lc;
> ListCell *start = lnext(list_head(childrel->live_partitioned_rels));
>
> for_each_cell(lc, start)
> partitioned_rels = lappend_int(partitioned_rels,
> lfirst_int(lc));
> }
>
> Although it seems pretty fragile. It would probably be better to find
> a nicer way of handling all this.

Hi Amit,

I also noticed earlier that this is still broken in v19.

--
David Rowley http://www.2ndQuadrant.com/
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