On Tue, May 26, 2020 at 3:04 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Mon, May 25, 2020 at 8:07 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> >
> > On Fri, May 22, 2020 at 11:54 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > >
> > > 4.
> > > + * XXX Do we need to allocate it in TopMemoryContext?
> > > + */
> > > +static void
> > > +subxact_info_add(TransactionId xid)
> > > {
> > > ..
> > >
> > > For this and other places in a patch like in function
> > > stream_open_file(), instead of using TopMemoryContext, can we consider
> > > using a new memory context LogicalStreamingContext or something like
> > > that. We can create LogicalStreamingContext under TopMemoryContext. I
> > > don't see any need of using TopMemoryContext here.
> >
> > But, when we will delete/reset the LogicalStreamingContext?
> >
>
> Why can't we reset it at each stream stop message?
> > because
> > we are planning to keep this memory until the worker is alive so that
> > supposed to be the top memory context.
> >
>
> Which part of allocation do we want to keep till the worker is alive?
static TransactionId *xids = NULL; we need to keep till worker life space.
> Why we need memory-related to subxacts till the worker is alive? As
> we have now, after reading subxact info (subxact_info_read), we need
> to ensure that it is freed after its usage due to which we need to
> remember and perform pfree at various places.
>
> I think we should once see the possibility that such that we could
> switch to this new context in start stream message and reset it in
> stop stream message. That might help in avoiding
> MemoryContextSwitchTo TopMemoryContext at various places.
Ok, I understand, I think subxacts can be allocated in new
LogicalStreamingContext which we can reset at the stream stop. How
about xids?
shall we create another context that will stay until the worker lifespan?
> > If we create any other context
> > with the same life span as TopMemoryContext then what is the point?
>>
>
> It is helpful for debugging. It is recommended that we don't use the
> top memory context unless it is really required. Read about it in
> src/backend/utils/mmgr/README.
I see.
--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com