Re: Memory-Bounded Hash Aggregation

On 28/12/2019 01:35, Jeff Davis wrote:
> I've attached a new patch that adds some basic costing for disk during
> hashagg.

This patch (hashagg-20191227.patch) doesn't compile:

nodeAgg.c:3379:7: error: ‘hashagg_mem_overflow’ undeclared (first use in 
this function)
    if (hashagg_mem_overflow)
        ^~~~~~~~~~~~~~~~~~~~

Looks like the new GUCs got lost somewhere between 
hashagg-20191220.patch and hashagg-20191227.patch.

> /*
>  * find_aggregated_cols
>  *      Construct a bitmapset of the column numbers of aggregated Vars
>  *      appearing in our targetlist and qual (HAVING clause)
>  */
> static Bitmapset *
> find_aggregated_cols(AggState *aggstate)
> {
>     Agg           *node = (Agg *) aggstate->ss.ps.plan;
>     Bitmapset  *colnos = NULL;
>     ListCell   *temp;
> 
>     /*
>      * We only want the columns used by aggregations in the targetlist or qual
>      */
>     if (node->plan.targetlist != NULL)
>     {
>         foreach(temp, (List *) node->plan.targetlist)
>         {
>             if (IsA(lfirst(temp), TargetEntry))
>             {
>                 Node *node = (Node *)((TargetEntry *)lfirst(temp))->expr;
>                 if (IsA(node, Aggref) || IsA(node, GroupingFunc))
>                     find_aggregated_cols_walker(node, &colnos);
>             }
>         }
>     }

This makes the assumption that all Aggrefs or GroupingFuncs are at the 
top of the TargetEntry. That's not true, e.g.:

select 0+sum(a) from foo group by b;

I think find_aggregated_cols() and find_unaggregated_cols() should be 
merged into one function that scans the targetlist once, and returns two 
Bitmapsets. They're always used together, anyway.

- Heikki