Re: Improve eviction algorithm in ReorderBuffer - Mailing list pgsql-hackers

On Tue, Mar 12, 2024 at 4:23 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Fri, Mar 8, 2024 at 12:58 PM Peter Smith <smithpb2250@gmail.com> wrote:
> >
...
> > > > 5.
> > > > + *
> > > > + * If 'indexed' is true, we create a hash table to track of each node's
> > > > + * index in the heap, enabling to perform some operations such as removing
> > > > + * the node from the heap.
> > > >   */
> > > >  binaryheap *
> > > > -binaryheap_allocate(int capacity, binaryheap_comparator compare, void *arg)
> > > > +binaryheap_allocate(int capacity, binaryheap_comparator compare,
> > > > + bool indexed, void *arg)
> > > >
> > > > BEFORE
> > > > ... enabling to perform some operations such as removing the node from the heap.
> > > >
> > > > SUGGESTION
> > > > ... to help make operations such as removing nodes more efficient.
> > > >
> > >
> > > But these operations literally require the indexed binary heap as we
> > > have an assertion:
> > >
> > > void
> > > binaryheap_remove_node_ptr(binaryheap *heap, bh_node_type d)
> > > {
> > >     bh_nodeidx_entry *ent;
> > >
> > >     Assert(!binaryheap_empty(heap) && heap->bh_has_heap_property);
> > >     Assert(heap->bh_indexed);
> > >
> >
> > I didn’t quite understand -- the operations mentioned are "operations
> > such as removing the node", but binaryheap_remove_node() also removes
> > a node from the heap. So I still felt the comment wording of the patch
> > is not quite correct.
>
> Now I understand your point. That's a valid point.
>
> >
> > Now, if the removal of a node from an indexed heap can *only* be done
> > using binaryheap_remove_node_ptr() then:
> > - the other removal functions (binaryheap_remove_*) probably need some
> > comments to make sure nobody is tempted to call them directly for an
> > indexed heap.
> > - maybe some refactoring and assertions are needed to ensure those
> > *cannot* be called directly for an indexed heap.
> >
>
> If the 'index' is true, the caller can not only use the existing
> functions but also newly added functions such as
> binaryheap_remove_node_ptr() and binaryheap_update_up() etc. How about
> something like below?
>

You said: "can not only use the existing functions but also..."

Hmm. Is that right? IIUC those existing "remove" functions should NOT
be called directly if the heap was "indexed" because they'll delete
the node from the heap OK, but any corresponding index for that
deleted node will be left lying around -- i.e. everything gets out of
sync. This was the reason for my original concern.

>  * If 'indexed' is true, we create a hash table to track each node's
>  * index in the heap, enabling to perform some operations such as
>  * binaryheap_remove_node_ptr() etc.
>

Yeah, something like that... I'll wait for the next patch version
before commenting further.

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Kind Regards,
Peter Smith.
Fujitsu Australia