Re: [HACKERS] Pluggable storage

On Tue, Aug 1, 2017 at 1:56 PM, Haribabu Kommi <kommi.haribabu@gmail.com> wrote:
>
>
> On Sun, Jul 23, 2017 at 4:10 PM, Amit Kapila <amit.kapila16@gmail.com>
> wrote:
>>
>
>>
>> > 1. Design an API that returns values/nulls array and convert that into a
>> > HeapTuple whenever it is required in the upper layers. All the existing
>> > heap form/deform tuples are used for every tuple with some adjustments.
>> >
>>
>> So, this would have the additional cost of form/deform.  Also, how
>> would it have lesser changes as compare to what you have described
>> earlier?
>
>
> Yes, It have the additional cost of form/deform. It is the same approach
> that
> is described earlier. But I have an intention of modifying everywhere the
> HeapTuple is accessed. But with the other prototype changes of removing
> HeapTuple usage from triggers, I realized that it needs some clear design
> to proceed further, instead of combining those changes with pluggable
> Storage API.
>
> - heap_getnext function is kept as it as and it is used only for system
> table
>   access.
> - heap_getnext_slot function is introduced to return the slot whenever the
>   data is found, otherwise NULL, This function is used in all the places
> from
>   Executor and etc.
>
> - The TupleTableSlot structure is modified to contain a void* tuple instead
> of
> HeapTuple. And also it contains the storagehanlder functions.
> - heap_insert and etc function can take Slot as an argument and perform the
> insert operation.
>
> The cases where the TupleTableSlot is not possible to sent, form a HeapTuple
> from the data and sent it and also note down that it is a HeapTuple data,
> not
> the tuple from the storage.
>
..
>
>
>>
>> > 3. Design an API that returns StorageTuple(void *) but the necessary
>> > format information of that tuple can be get from the tupledesc. wherever
>> > the tuple is present, there exists a tupledesc in most of the cases. How
>> > about adding some kind of information in tupledesc to find out the tuple
>> > format and call the necessary functions
>> >
>
>
> heap_getnext function returns StorageTuple instead of HeapTuple. The tuple
> type information is available in the TupleDesc structure.
>
> All heap_insert and etc function accepts TupleTableSlot as input and perform
> the insert operation. This approach is almost same as first approach except
> the
> storage handler functions are stored in TupleDesc.
>

Why do we need to store handler function in TupleDesc?  As of now, the
above patch series has it available in RelationData and
TupleTableSlot, I am not sure if instead of that keeping it in
TupleDesc is a good idea.  Which all kind of places require TupleDesc
to contain handler?  If those are few places, can we think of passing
it as a parameter?


-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com